ArticleLiterature Review

Movement Vigor as a Reflection of Subjective Economic Utility

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Abstract

To understand subjective evaluation of an option, various disciplines have quantified the interaction between reward and effort during decision making, producing an estimate of economic utility, namely the subjective ‘goodness’ of an option. However, variables that affect utility of an option also influence the vigor of movements toward that option. For example, expectation of reward increases speed of saccadic eye movements, whereas expectation of effort decreases this speed. These results imply that vigor may serve as a new, real-time metric with which to quantify subjective utility, and that the control of movements may be an implicit reflection of the brain's economic evaluation of the expected outcome.

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... The invigorating effect of average reward is in agreement with previous work (Beierholm et al., 2013;Guitart-Masip et al., 2011;Niv et al., 2007;Otto & Daw, 2019;Shadmehr et al., 2019) and with models of reward-related vigor (Lemon, 1991;Niv et al., 2007;Shadmehr et al., 2019). We speculated that the average reward rate would have a decreased effect on vigor in older subjects because age-related declines in dopamine function relate to decreased performance in probabilistic reward-learning tasks (de Boer et al., 2017;Eppinger et al., 2011;Mell et al., 2005). ...
... The invigorating effect of average reward is in agreement with previous work (Beierholm et al., 2013;Guitart-Masip et al., 2011;Niv et al., 2007;Otto & Daw, 2019;Shadmehr et al., 2019) and with models of reward-related vigor (Lemon, 1991;Niv et al., 2007;Shadmehr et al., 2019). We speculated that the average reward rate would have a decreased effect on vigor in older subjects because age-related declines in dopamine function relate to decreased performance in probabilistic reward-learning tasks (de Boer et al., 2017;Eppinger et al., 2011;Mell et al., 2005). ...
... We speculated that the average reward rate would have a decreased effect on vigor in older subjects because age-related declines in dopamine function relate to decreased performance in probabilistic reward-learning tasks (de Boer et al., 2017;Eppinger et al., 2011;Mell et al., 2005). Research indicates that that individual levels of vigor vary across a population (Bargary et al., 2017;Choi et al., 2014;Reppert et al., 2018;Shadmehr et al., 2019). Some people are more willing to exert effort (Treadway et al., 2009), and this correlates with the extent of amphetamine induced dopamine release in the striatum and prefrontal cortex as measured using PET (Treadway et al., 2012). ...
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Vigor reflects how motivated one is to respond to a stimulus. We previously showed that humans are more vigorous when more reward is available on average, and that this relationship is modulated by the dopamine precursor levodopa. Dopamine signalling and probabilistic reward learning degrade with age, so the relationship between vigor and reward should change with age. We test this and assess whether the relationship between vigor and reward correlates with D1 dopamine receptor availability measured using Positron Emission Tomography. We measured response times of 30 older and 30 younger subjects during an oddball discrimination task where rewards varied systematically between trial. Reward rate had a similar impact on the vigor of both groups. We observed a weak positive association across subjects between ventral striatal dopamine receptor availability and effect of average reward rate on response time, which was in the opposite direction to our prediction. Overall, the effect of reward on response vigor is similar between younger and older humans and is weakly sensitive to dopamine D1 receptor availability.
... Autism Spectrum Disorders comprise a range of heterogeneous neurodevelopmental disorders that manifest in early childhood and present with abnormal motor and social behaviors [37][38][39][40][41]. Like schizophrenia, individuals with this disorder present with a diverse symptomatology. ...
... Autism Spectrum Disorders comprise a range of heterogeneous neurodevelopmental disorders that manifest in early childhood and present with abnormal motor and social behaviors [37][38][39][40][41]. Like schizophrenia, individuals with this disorder present with a diverse symptomatology. ASD-associated behavioral deficits are classically grouped into three domains: impaired social interaction, deficits in communication and restrictive, repetitive patterns of interest and behavior [8,37,[39][40][41]. While these deficits have dominated thought on autism symptomology, cognitive and sensory deficits have long been recognized comorbidities of this disorder [37,42] Estimates for ASD prevalence range from 0.4% [38] to approximately 1% [42]. ...
... While there have been doubts about the ability of mice to perform the complex cognitive tasks required to assess value-based choice [27,35,36], recent work contradicts this idea [37][38][39]. As in rat, choice selection under outcome uncertainty has successfully been modeled with alternatives of varying reward probability [37,38,40]. In addition, the integration of choice benefit and cost has been explored within the context of delayed discounting, whereby larger reward volumes are associated with longer temporal delay to reward delivery [41][42][43]. ...
Article
The ability to select actions based on internalized goals is a significant domain of animal fitness, and particularly crucial in humans. These behaviors are guided by an ability to weigh the positive and negative effects of an action and to learn from experience. Individuals with neuropsychiatric disorders share common defects in this cognitive domain, yet a circuit understanding of this computational dysfunction is unclear. Further progress requires a closer association between the genes that cause neuropsychiatric disorders and the circuits that underlie observed abnormalities. In this thesis, I begin by with an overview of current nosological and etiological understanding of neuropsychiatric disease as well as current challenges in developing circuit hypotheses of dysfunction. I move on to characterize a quantitative multidimensional behavioral assay in mice that gives key insight into value-based action in this model system. Because of its role in regulating motor output and reinforcement learning, the striatum was identified as a potential circuit junction mediating critical cognitive computations. In vivo imaging of the direct and indirect pathway of the dorsomedial striatum revealed broad overlap in encoding reward costs and benefits in these cell populations, with the indirect pathway acting as a circuit substrate for cost-benefit interactions. Finally, we leveraged these techniques to characterize goal-directed dysfunction in the Nrxn1α model of neuropsychiatric dysfunction. We isolated this deficit to excitatory projections from forebrain regions using conditional region-specific ablations of Nrxn1α. In these mice, we observed abnormalities in encoding features of reward that serve as the circuit correlate to observed choice abnormalities. In sum then, this thesis attempts to synthesize quantitative behavioral, genetic and in vivo physiological techniques to characterize a circuit intermediary between genetic mutations and neuropsychiatric cognitive symptoms.
... Among costs, both duration and energy expenditure discount the value of rewards (Shadmehr et al., 2019;Shadmehr and Ahmed, 2020). As a consequence, individuals tend to decide and act in a way that reduces these costs. ...
... Indeed, for anyone making a decision, the most adaptive strategy is to choose options that maximize one's global reward rate (Bogacz et al., 2010;Balci et al., 2011), which occurs when both decision and action are sufficiently accurate but not overly effortful and time consuming. In this view, decision and action define a continuum, coordinated by unified or interacting choice and motor regulation signals (Thura andCisek, 2016, 2017;Cisek and Thura, 2018;Carland et al., 2019;Shadmehr et al., 2019). Recent observations support such coordination between decision and action during goal-directed behavior (Thura et al., 2014;Yoon et al., 2018;Reynaud et al., 2020;Thura, 2020). ...
... In the present study, however, subjects could not reduce movement duration. It is thus possible that the larger temporal discounting of reward expected by subjects in this context reduced their implicit motivation to behave (Mazzoni et al., 2007;Shadmehr et al., 2019), leading to longer reaction times. By contrast, almost half of the subjects reduced their decision durations in the Time condition of the choice task compared to a control condition. ...
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Recent theories and data suggest that adapted behavior involves economic computations during which multiple trade-offs between reward value, accuracy requirement, energy expenditure, and elapsing time are solved so as to obtain rewards as soon as possible while spending the least possible amount of energy. However, the relative impact of movement energy and duration costs on perceptual decision-making and movement initiation is poorly understood. Here, we tested 31 healthy subjects on a perceptual decision-making task in which they executed reaching movements to report probabilistic choices. In distinct blocks of trials, the reaching duration (“Time” condition) and energy (“Effort” condition) costs were independently varied compared to a “Reference” block, while decision difficulty was maintained similar at the block level. Participants also performed a simple delayed-reaching (DR) task aimed at estimating movement initiation duration in each motor condition. Results in that DR task show that long duration movements extended reaction times (RTs) in most subjects, whereas energy-consuming movements led to mixed effects on RTs. In the decision task, about half of the subjects decreased their decision durations (DDs) in the Time condition, while the impact of energy on DDs were again mixed across subjects. Decision accuracy was overall similar across motor conditions. These results indicate that movement duration and, to a lesser extent, energy expenditure, idiosyncratically affect perceptual decision-making and action initiation. We propose that subjects who shortened their choices in the time-consuming condition of the decision task did so to limit a drop of reward rate.
... Among healthy individuals, there is well-recognized diversity in movement vigor, with some people tending to consistently move rapidly, whereas others tend to move slowly, as evidenced by their saccades (i.e., rapid, ballistic eye movements) [64][65][66] and their reaching movements [64]. Consequently, in recent years, the speed at which people move has been conceptualized as a trait-like attribute [64,67]. Accordingly, we examined the relationship between performance times (as a proxy for speed) among a series of lower and upper extremity tasks that, conceptually, challenge different physiological systems (e.g., some challenge muscle strength, while others challenge dexterity/motor coordination). ...
... Analysis 3. Movement speed in older adults as a traitlike attribute of individuality Movement vigor, a term that has largely arisen from the field of neuroeconomics, is commonly used in the context of describing elementary, stimulus-driven movements, such as saccades and reaching [67]. The operational definition is typically the inverse of the time from stimulus onset to movement completion, conditioned on distance (i.e., combination of reaction time and velocity) [67,139]. ...
... Analysis 3. Movement speed in older adults as a traitlike attribute of individuality Movement vigor, a term that has largely arisen from the field of neuroeconomics, is commonly used in the context of describing elementary, stimulus-driven movements, such as saccades and reaching [67]. The operational definition is typically the inverse of the time from stimulus onset to movement completion, conditioned on distance (i.e., combination of reaction time and velocity) [67,139]. While classic theories in motor control suggest that differences in movement vigor reflect a speed accuracy trade-off [140], recent data examining these competing hypotheses provided strong evidence indicating that movement vigor has no impact on end-point accuracy [141]. ...
Article
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The capacity to move is essential for independence and declines with age. Slow movement speed, in particular, is strongly associated with negative health outcomes. Prior research on mobility (herein defined as movement slowness) and aging has largely focused on musculoskeletal mechanisms and processes. More recent work has provided growing evidence for a significant role of the nervous system in contributing to reduced mobility in older adults. In this article, we report four pieces of complementary evidence from behavioral, genetic, and neuroimaging experiments that, we believe, provide theoretical support for the assertion that the basal ganglia and its dopaminergic function are responsible, in part, for age-related reductions in mobility. We report four a posteriori findings from an existing dataset: (1) slower central activation of ballistic force development is associated with worse mobility among older adults; (2) older adults with the Val/Met intermediate catecholamine-O-methyl-transferase (COMT) genotype involved in dopamine degradation exhibit greater mobility than their homozygous counterparts; (3) there are moderate relationships between performance times from a series of lower and upper extremity tasks supporting the notion that movement speed in older adults is a trait-like attribute; and (4) there is a relationship of functional connectivity within the medial orbofrontal (mOFC) cortico-striatal network and measures of mobility, suggesting that a potential neural mechanism for impaired mobility with aging is the deterioration of the integrity of key regions within the mOFC cortico-striatal network. These findings align with recent basic and clinical science work suggesting that the basal ganglia and its dopaminergic function are mechanistically linked to age-related reductions in mobility capacity.
... Importantly, the reward-related increase in saccades' peak velocity cannot be fully explained by the stereotypic relationship between saccades' velocity and amplitude known as "main sequence" (19), demonstrating that reward incentives affect saccades' velocity above and beyond biomechanical factors. Similar results were found in human psychophysics studies as monetary rewards were shown to increase saccade velocity (20) and vigor, that is, the peak velocity as a function of amplitude (21)(22)(23). ...
... Saccades play a pivotal role in acquiring sensory information across space and are closely linked to attentional selection. Previous studies have shown that saccade metrics could be used to probe different aspects of decision making in both perceptual (58) as well as value-based decision making (22). Our study furthers these previous findings and additionally shows that saccades provide detailed and precise information regarding how one of the most complex aspects of human cognition, namely that of conscious awareness, is orchestrated. ...
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Over the last decades, several studies have demonstrated that conscious and unconscious reward incentives both affect performance in physical and cognitive tasks, suggesting that goal-pursuit can arise from an unconscious will. Whether the planning of goal-directed saccadic eye movements during an effortful task can also be affected by subliminal reward cues has not been systematically investigated. We employed a novel task where participants made several eye movements back and forth between a fixation point and a number of peripheral targets. The total number of targets visited by the eyes in a fixed amount of time determined participants' monetary gain. The magnitude of the reward at stake was briefly shown at the beginning of each trial and masked by pattern images superimposed in time so that at shorter display durations participants perceived reward incentives subliminally. We found a main effect of reward across all display durations as higher reward enhanced participants' oculomotor effort measured as the frequency and peak velocity of saccades. This effect was strongest for consciously perceived rewards but also occurred when rewards were subliminally perceived. Although we did not find a statistically significant dissociation between the reward-related modulation of different saccadic parameters, across two experiments the most robust effect of subliminal rewards was observed for the modulation of the saccadic frequency but not the peak velocity. These results suggest that multiple indices of oculomotor effort can be incentivized by subliminal rewards and that saccadic frequency may provide the most sensitive indicator of subliminal incentivization of eye movements.
... The prospect of reward can positively shape both the speed and precision of behavior [30,[45][46][47], and several lines of evidence suggest that dopamine may play a key role in mediating aspects of both processes [24,26,29,30,48]. As expected, rats' performance in the current experiment was strongly affected by the reward size on offer. ...
... Cues associated with a large future reward reduced action latencies to complete each element of the action sequence. This finding is consistent with the notion that there is a direct link between the vigor of actions-the reciprocal of the time to complete an action sequence [47]-and the net gain from obtaining the potential reward [24,49,50]. However, there was an asymmetric influence on response accuracy; the prospect of a large reward improved Go trial accuracy, but had no reliable effect on successful No-Go trial completion. ...
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It is well established that dopamine transmission is integral in mediating the influence of reward expectations on reward-seeking actions. However, the precise causal role of dopamine transmission in moment-to-moment reward-motivated behavioral control remains contentious, particularly in contexts where it is necessary to refrain from responding to achieve a beneficial outcome. To examine this, we manipulated dopamine transmission pharmacologically as rats performed a Go/No-Go task that required them to either make or withhold action to gain either a small or large reward. D1R Stimulation potentiated cue-driven action initiation, including fast impulsive actions on No-Go trials. By contrast, D1R blockade primarily disrupted the successful completion of Go trial sequences. Surprisingly, while after global D1R blockade this was characterized by a general retardation of reward-seeking actions, nucleus accumbens core (NAcC) D1R blockade had no effect on the speed of action initiation or impulsive actions. Instead, fine-grained analyses showed that this manipulation decreased the precision of animals’ goal-directed actions, even though they usually still followed the appropriate response sequence. Strikingly, such “unfocused” responding could also be observed off-drug, particularly when only a small reward was on offer. These findings suggest that the balance of activity at NAcC D1Rs plays a key role in enabling the rapid activation of a focused, reward-seeking state to enable animals to efficiently and accurately achieve their goal.
... A number of models have been proposed to account for the computations in basal ganglia that underlie its role in specifying the speed and amplitude of movement (10,27,28,(30)(31)(32). A common feature of these models is that descending cortical motor commands are carried to the STR where basal ganglia circuits may modulate the gain (27) of descending motor commands [termed movement vigor (26,33)] or implement a closed-loop feedback to shape movement kinematics (31) and/or act as a primary source of motor commands for stereotyped movement trajectories (28,32). In contrast to basal pons deficits, inactivation of dorsal STR (dSTR) modifies movement speed and amplitude while often leaving movement target direction unaffected (21,22,24,34). ...
... In contrast, perturbations of basal ganglia function often lead to aberrant control of movement amplitude and speed (22,24,26,30,63). Basal ganglia pathways have been proposed to control movement amplitude/speed either by adaptively adjusting the gain of motor commands on the basis of reward feedback [referred to as movement vigor (26,27,33)] or by determining a reference signal for a continuous feedback controller (31) or by producing motor commands per se (32). In the context of the current experiments, these models all make similar predictions and thus cannot be distinguished in detail but are broadly consistent with a pathway involving corticostriatal IT and dSTR neurons being a critical module involved in descending forebrain control of movement amplitude. ...
Article
The interaction of descending neocortical outputs and subcortical premotor circuits is critical for shaping skilled movements. Two broad classes of motor cortical output projection neurons provide input to many subcortical motor areas: pyramidal tract (PT) neurons, which project throughout the neuraxis, and intratelencephalic (IT) neurons, which project within the cortex and subcortical striatum. It is unclear whether these classes are functionally in series or whether each class carries distinct components of descending motor control signals. Here, we combine large-scale neural recordings across all layers of motor cortex with cell type-specific perturbations to study cortically dependent mouse motor behaviors: kinematically variable manipulation of a joystick and a kinematically precise reach-to-grasp. We find that striatum-projecting IT neuron activity preferentially represents amplitude, whereas pons-projecting PT neurons preferentially represent the variable direction of forelimb movements. Thus, separable components of descending motor cortical commands are distributed across motor cortical projection cell classes.
... Although the hippocampus is potentially involved in skill learning tasks involving the flexible selection of force parameters (i.e., as in the current study, , its engagement may have been limited as learning did not involve a strong spatial or perceptual component. Another complementary interpretation is that rewards delivered after a long delay are temporally discounted and perceived as subjectively less valuable relative to when the delay is short (Shadmehr et al., 2010(Shadmehr et al., , 2019, reducing their beneficial effect on offline consolidation mechanisms (Ambrose et al., 2016;Sterpenich et al., 2021). ...
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Reward timing, that is, the delay after which reward is delivered following an action is known to strongly influence reinforcement learning. Here, we asked if reward timing could also modulate how people learn and consolidate new motor skills. In 60 healthy participants, we found that delaying reward delivery by a few seconds influenced motor learning. Indeed, training with a short reward delay (1 s) induced continuous improvements in performance, while a long reward delay (6 s) led to initially high learning rates that were followed by an early plateau in the learning curve and a lower performance at the end of training. Participants who learned the skill with a long reward delay also exhibited reduced overnight memory consolidation. Overall, our data show that reward timing affects the dynamics and consolidation of motor learning, a finding that could be exploited in future rehabilitation programs.
... Thus, the combination of biophysical membrane properties of burst neurons and the output of OPNs can determine the velocity of the saccade. This mechanism may provide an explanation for the observed variation in saccade velocity (also referred to as vigor) with task conditions (e.g., Manohar et al., 2015;Shadmehr et al., 2019). ...
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The goal of this short review is to call attention to a yawning gap of knowledge that separates two processes essential for saccade production. On the one hand, knowledge about the saccade generation circuitry within the brainstem is detailed and precise – push-pull interactions between gaze-shifting and gaze-holding processes control the time of saccade initiation, which begins when omnipause neurons are inhibited and brainstem burst neurons are excited. On the other hand, knowledge about the cortical and subcortical premotor circuitry accomplishing saccade initiation has crystalized around the concept of stochastic accumulation – the accumulating activity of saccade neurons reaching a fixed value triggers a saccade. Here is the gap: we do not know how the reaching of a threshold by premotor neurons causes the critical pause and burst of brainstem neurons that initiates saccades. Why this problem matters and how it can be addressed will be discussed. Closing the gap would unify two rich but curiously disconnected empirical and theoretical domains.
... In this view, altered activity in specific neural structures (e.g., in the case of reward processing, midbrain dopaminergic neurons; Schultz, 2015) could produce changes in both selection and execution processes at the behavioral level. The roots of this idea lie so deep within the field that researchers often consider RTs and MTs together as a single measure, thought to reflect action vigor (Shadmehr et al., 2019). The findings of Codol et al. (2020) ask us to reconsider carefully this vision, suggesting that, in some conditions, the speed of action selection and execution can be regulated by independent (yet likely interacting) neural structures. ...
Article
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The mere possibility of earning a reward induces substantial improvements in the way we choose and execute actions. This observation has raised hope for rehabilitation: reward is regarded as a promising means to magnify the positive effects of practice on motor control. Yet, this branch of research is only burgeoning, and neuroscientists have yet to identify the mechanisms through which reward improves movements. In this Journal Club, we discuss the recent results of Codol et al., 2020, showing that the presence of reward can have dissociable impacts on action selection and execution with effects on the latter process associated with increased arm stiffness. These findings provide mechanistic insights for theories of motor control and have implications for future clinical translation.
... For instance, it has been found that the opportunity to earn money increases accuracy in a reaching task (Gajda et al., 2016). Moreover, motivation enhances the velocity with which humans move (Sackaloo et al., 2015;Shadmehr et al., 2019). Finally, motivation might reduce the speedaccuracy trade-off as eye movements to more rewarding targets are not only faster but also more accurate (Manohar et al., 2015). ...
Article
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It is well-established that intermediate challenge is optimally motivating. We tested whether this can be quantified into an inverted-U relationship between motivation and success frequency. Participants played a game in which they navigated a scene to catch targets. In Experiment 1 ( N = 101), play duration was free and the motivating value of success frequency was measured from the probability that a player would continue at that frequency. In Experiment 2 ( N = 70), play duration was fixed, and motivation was measured using repeated self-reports. In Experiment 1, the probability to continue increased linearly with the success frequency whereas play duration did show the inverted-U relationship with success frequency. In Experiment 2, self-reported motivation showed the inverted-U relationship with success frequency. Together, this shows that motivation depends on success frequency. In addition, we provide tentative evidence that the concept of intermediate challenge being most motivating can be quantified into an inverted-U relationship between motivation and success frequency.
... Motor performance and particularly movement speed and reaction time-termed 'vigor'-are highly influenced by relative neurological effort-reward calculations occurring within the basal ganglia and associated dopaminergic system [62,203]. Dopamine-a neurotransmitter-is produced in midbrain neurons that send their axons throughout the brain [26]. ...
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Youth athletes are ideal candidates for novel therapeutic motor learning interventions that leverage the plasticity of the central nervous system to promote desirable biomechanical adaptions. We summarize the empirical data supporting the three pillars of the Optimizing Performance Through Intrinsic Motivation and Attention for Learning (OPTIMAL) theory of motor learning and expand on potential neurophysiologic mechanisms that will support enhanced movement mechanics in youth to optimize prevention programs for reduced injury risk, injury rehabilitation, exercise performance, and play (Prevention Rehabilitation Exercise Play; PREP). Specifically, we highlight the role of motivational factors to promote the release of dopamine that could accelerate motor performance and learning adaptations. Further, we detail the potential for an external focus of attention to shift attentional allocation and increase brain activity in regions important for sensorimotor integration to facilitate primary motor cortex efficiency. This manuscript serves to provide the most current data in support of the application of OPTIMAL PREP training strategies of the future.
... Note that rewards followed the successful execution of CF saccades, whereas CP saccades were needed to get ready for a new trial, yet not followed by an immediate reward. Hence, the higher speed and shorter duration of CF saccades, their larger vigor, may be a consequence of more immediate reward expectations [42][43][44][45][46]. ...
Article
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Purkinje cell (PC) discharge, the only output of cerebellar cortex, involves 2 types of action potentials, high-frequency simple spikes (SSs) and low-frequency complex spikes (CSs). While there is consensus that SSs convey information needed to optimize movement kinematics, the function of CSs, determined by the PC’s climbing fiber input, remains controversial. While initially thought to be specialized in reporting information on motor error for the subsequent amendment of behavior, CSs seem to contribute to other aspects of motor behavior as well. When faced with the bewildering diversity of findings and views unraveled by highly specific tasks, one may wonder if there is just one true function with all the other attributions wrong? Or is the diversity of findings a reflection of distinct pools of PCs, each processing specific streams of information conveyed by climbing fibers? With these questions in mind, we recorded CSs from the monkey oculomotor vermis deploying a repetitive saccade task that entailed sizable motor errors as well as small amplitude saccades, correcting them. We demonstrate that, in addition to carrying error-related information, CSs carry information on the metrics of both primary and small corrective saccades in a time-specific manner, with changes in CS firing probability coupled with changes in CS duration. Furthermore, we also found CS activity that seemed to predict the upcoming events. Hence PCs receive a multiplexed climbing fiber input that merges complementary streams of information on the behavior, separable by the recipient PC because they are staggered in time.
... Those data can, of course, be used to test important hypotheses. But they obscure information beyond simple preference, such as motivation, arousal, attentional locus, and vigor (e.g., Niv et al., 2007;Shadmehr et al., 2019). In contrast, behavioral tracking can produce high quantities of data (for example, thirteen keypoints in 3D sampled at 30 Hz, Bala et al., 2020) without human intervention. ...
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Understanding primate behavior is a mission-critical goal of both biology and biomedicine. Despite the importance of behavior, our ability to rigorously quantify it has heretofore been limited to low-information measures like preference, looking time, and reaction time, or to non-scaleable measures like ethograms. However, recent technological advances have led to a major revolution in behavioral measurement. Specifically, digital video cameras and automated pose tracking software can provide detailed measures of full body position (i.e., pose) of multiple primates over time (i.e., behavior) with high spatial and temporal resolution. Pose-tracking technology in turn can be used to detect behavioral states, such as eating, sleeping, and mating. The availability of such data has in turn spurred developments in data analysis techniques. Together, these changes are poised to lead to major advances in scientific fields that rely on behavioral as a dependent variable. In this review, we situate the tracking revolution in the history of the study of behavior, argue for investment in and development of analytical and research techniques that can profit from the advent of the era of big behavior, and propose that zoos will have a central role to play in this era.
... When incentivised on this task, people expend more effort and also have a higher expectation of reward, which is linked to the effort they expend. Therefore it is possible that the CNV is measuring the greater expected reward induced by motivation, which is linked to faster saccades (Haith, Reppert, & Shadmehr, 2012;Shadmehr, Reppert, Summerside, Yoon, & Ahmed, 2019). The fact that no associations were seen between behaviour and neural activity in the time-430 window before the preparation cue might suggest that factors such as expected reward or arousal are less likely to explain our results. ...
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Motivation depends on dopamine, but might be modulated by acetylcholine which influences dopamine release in the striatum, and amplifies motivation in animal studies. A corresponding effect in humans would be important clinically, since anticholinergic drugs are frequently used in Parkinson’s disease, a condition that can also disrupt motivation. Reward and dopamine make us more ready to respond, as indexed by reaction times (RT), and move faster, sometimes termed vigour. These effects may be controlled by preparatory processes that can be tracked using EEG. We measured vigour in a placebo-controlled, double-blinded study of trihexyphenidyl (THP), a muscarinic antagonist, with an incentivised eye movement task and EEG. Participants responded faster and with greater vigour when incentives were high, but THP blunted these motivation effects, suggesting that muscarinic receptors facilitate invigoration by reward. Preparatory EEG build-up (contingent negative variation; CNV) was strengthened by high incentives and by muscarinic blockade. The amplitude of preparatory activity predicted both vigour and RT, although over distinct scalp regions. Frontal activity predicted vigour, whereas a larger, earlier, central component predicted RT. Indeed the incentivisation of RT was partly mediated by the CNV, though vigour was not. Moreover, the CNV mediated the drug’s effect on dampening incentives, suggesting that muscarinic receptors underlie the motivational influence on this preparatory activity. Taken together, these findings show that a muscarinic blocker used to treat Parkinson’s disease impairs motivated action in healthy people, and that medial frontal preparatory neural activity mediates this for RT.
... In locomotion, metabolic costs have helped explain preferred walking speed, step length, step width and arm swing in healthy individuals [20][21][22][23]. When represented as metabolic cost, effort-based decision-making in reaching can account for both the choice of action and the vigour of the ensuing movements [24][25][26][27]. Metabolic costs are also used to explain foraging decisions in a range of animals [28][29][30][31]. ...
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Economists have known for centuries that to understand an individual's decisions, we must consider not only the objective value of the goal at stake, but its subjective value as well. However, achieving that goal ultimately requires expenditure of effort. Surprisingly, despite the ubiquitous role of effort in decision-making and movement, we currently do not understand how effort is subjectively valued in daily movements. Part of the difficulty arises from the lack of an objective measure of effort. Here, we use a physiological approach to address this knowledge gap. We quantified objective effort costs by measuring metabolic cost via expired gas analysis as participants performed a reaching task against increasing resistance. We then used neuroeconomic methods to quantify each individual's subjective valuation of effort. Rather than the diminishing sensitivity observed in reward valuation, effort was valued objectively, on average. This is significantly less than the near-quadratic sensitivity to effort observed previously in force-based motor tasks. Moreover, there was significant inter-individual variability with many participants undervaluing or overvaluing effort. These findings demonstrate that in contrast with monetary decisions in which subjective value exhibits diminishing marginal returns, effort costs are valued more objectively in low-effort reaching movements common in daily life.
... In contrast, increasing evidence favors an alternative hypothesis that intermediate responses reflect a strategy to improve performance; such a strategy delays commitment to one option until more information can be attained and minimizes the cost of generating motor corrections (Alhussein and Smith,4 relative desirability of the two options. In particular, prior research has demonstrated that individuals consider both the potential rewards available in the environment as well as the likelihood with which they will be successful at attaining those rewards (for reviews, see Shadmehr et al., 2019;Wolpert and Landy, 2012). Both when choices are discrete (e.g., direct reaches or saccades) as well as when intermediate movements are generated, movements tend to be biased toward the more rewarding (Chapman et al., 2015;Liston and Stone, 2008;Sugrue et al., 2004) or likely (Chapman et al., 2010;Liston and Stone, 2008) option, reflecting an effort to maximize reward or task success respectively. ...
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When faced with multiple potential movement options, individuals either reach directly to one of the options, or initiate a reach intermediate between the options. It remains unclear why people generate these two types of behaviors. Using the go-before-you-know task (commonly used to study behavior under choice uncertainty), we examined two key questions. First, do these two types of responses reflect distinct movement strategies, or are they simply examples of a more general response to choice uncertainty? If the former, the relative desirability (i.e., weighing the likelihood of successfully hitting the target versus the attainable reward) of the two target options might be computed differently for direct versus intermediate reaches. We showed that indeed, when exogenous reward and success likelihood (i.e., endogenous reward) differ between the two options, direct reaches were more strongly biased by likelihood whereas intermediate movements were more strongly biased by reward. Second, what drives individual differences in how people respond under uncertainty? We found that risk/reward-seeking individuals generated a larger proportion of intermediate reaches and were more sensitive to trial-to-trial changes in reward, suggesting these movements reflect a strategy to maximize reward. In contrast, risk-adverse individuals tended to generate more direct reaches in an attempt to maximize success. Together, these findings suggest that when faced with choice uncertainty, individuals adopt movement strategies consistent with their risk/reward-seeking tendency, preferentially biasing behavior toward exogenous rewards or endogenous success and consequently modulating the relative desirability of the available options.
... A common and seemingly straightforward paradigm is to require participants to make actions associated with different expected amounts of reward. In these settings, humans and animals consistently make actions rapidly when they are associated with large reward and slowly when they are associated with less reward or no reward [1][2][3][4][5][6][7][8][9][10][11][12]. Remarkably, they do so even when this is a seemingly suboptimal strategy that substantially reduces their reward rate. ...
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Classic foraging theory predicts that humans and animals aim to gain maximum reward per unit time. However, in standard instrumental conditioning tasks individuals adopt an apparently suboptimal strategy: they respond slowly when the expected value is low. This reward-related bias is often explained as reduced motivation in response to low rewards. Here we present evidence this behavior is associated with a complementary increased motivation to search the environment for alternatives. We trained monkeys to search for reward-related visual targets in environments with different values. We found that the reward-related bias scaled with environment value, was consistent with persistent searching after the target was already found, and was associated with increased exploratory gaze to objects in the environment. A novel computational model of foraging suggests that this search strategy could be adaptive in naturalistic settings where both environments and the objects within them provide partial information about hidden, uncertain rewards.
... Vigor, often defined as reaction time plus speed of movements, has long been studied in the context of motor control (Choi et al., 2014;Rigas et al., 2016;Reppert et al., 2018). Recently, vigor has been appreciated as a reflection of value (Shadmehr et al., 2019). Vigor is increased by increasing reward (Summerside et al., 2018), decreased by increasing effort (Stelmach and Worringham, 1988), and modulated on short, individual-decision timescales (Reppert et al., 2015). ...
Chapter
Dynamic decision making requires an intact medial frontal cortex. Recent work has combined theory and single-neuron measurements in frontal cortex to advance models of decision making. We review behavioral tasks that have been used to study dynamic decision making and algorithmic models of these tasks using reinforcement learning theory. We discuss studies linking neurophysiology and quantitative decision variables. We conclude with hypotheses about the role of other cortical and subcortical structures in dynamic decision making, including ascending neuromodulatory systems.
... In several models considering sensorimotor noise, duration was selected as the minimum time to match a desired endpoint variance related to target's width, based on the speed-accuracy trade-off underlying visually-guided movements [8,[20][21][22]. Alternatively, a number of studies have assumed a "cost of time" (reflecting neuroeconomical processes related to decision-making and explicitly penalizing duration) to explain the preferred timing of movement [23][24][25][26][27][28][29][30]. ...
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Human movements with or without vision exhibit timing (i.e. speed and duration) and variability characteristics which are not well captured by existing computational models. Here, we introduce a stochastic optimal feedforward-feedback control (SFFC) model that can predict the nominal timing and trial-by-trial variability of self-paced arm reaching movements carried out with or without online visual feedback of the hand. In SFFC, movement timing results from the minimization of the intrinsic factors of effort and variance due to constant and signal-dependent motor noise, and movement variability depends on the integration of visual feedback. Reaching arm movements data are used to examine the effect of online vision on movement timing and variability, and test the model. This modelling suggests that the central nervous system predicts the effects of sensorimotor noise to generate an optimal feedforward motor command, and triggers optimal feedback corrections to task-related errors based on the available limb state estimate.
... reaching (Huang et al. 2012; Shadmehr et al. 2019), and influence a vast array of other animal 36 behaviors and actions (Alexander 1996). It seems possible that effort or energy do influence the 37 bell-shaped profile, but have gone unrecognized because of incomplete quantification of such 38 ...
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The central nervous system plans human reaching movements with stereotypically smooth kinematic trajectories and fairly consistent durations. Smoothness seems to be explained by accuracy as a primary movement objective, whereas duration seems to economize energy expenditure. But the current understanding of energy expenditure does not explain smoothness, so that two aspects of the same movement are governed by seemingly incompatible objectives. Here we show that smoothness is actually economical, because humans expend more metabolic energy for jerkier motions. The proposed mechanism is an underappreciated cost proportional to the rate of muscle force production, for calcium transport to activate muscle. We experimentally tested that energy cost in humans (N=10) performing bimanual reaches cyclically. The empirical cost was then demonstrated to predict smooth, discrete reaches, previously attributed to accuracy alone. A mechanistic, physiologically measurable, energy cost may therefore explain both smoothness and duration in terms of economy, and help resolve motor redundancy in reaching movements.
... The evidence as to whether it increases the actual amount and/or energy of movement remains inconclusive (Hove, Martinez, & Stupacher, 2020;Hurley, Martens, & Janata, 2014;Leman, Buhmann, & Van Dyck, 2017;Leow, Parrott, & Grahn, 2014;Witek, Popescu, Clarke, Hansen, Konvalinka, et al., 2017). Movement energy, defined more broadly as vigor, has emerged as a window on the interaction between reward prediction and motor control (Shadmehr, Reppert, Summerside, Yoon, & Ahmed, 2019). Depending on the nature of the task, vigor can correspond to quantities such as the speed with which one reaches to grasp a more or less desirable object or the energy with which ones is walking towards a goal (Shadmehr & Ahmed, 2020). ...
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The regularity of musical beat makes it a powerful stimulus promoting movement synchrony among people. Synchrony can increase interpersonal trust, affiliation and cooperation. Musical pieces can be classified according to the quality of groove; the higher the groove, the more it induces the desire to move. We investigated questions related to collective music-listening among 33 participants in an experiment conducted in a naturalistic yet acoustically controlled setting of a research concert hall with motion tracking. First, does higher groove music induce (i) movement with more energy and (ii) higher interpersonal movement coordination? Second, does visual social information manipulated by having eyes open or eyes closed also affect energy and coordination? Participants listened to pieces from four categories formed by crossing groove (high, low) with tempo (higher, lower). Their upper body movement was recorded via head markers. Self-reported ratings of grooviness, emotional valence, emotional intensity and familiarity were collected after each song. A biomechanically-motivated measure of movement energy increased with high-groove songs and was positively correlated with grooviness ratings, confirming the theoretically implied but less tested motor response to groove. Participants’ ratings of emotional valence and emotional intensity correlated positively with movement energy, suggesting that movement energy relates to emotional engagement with music. Movement energy was higher in eyes-open trials, suggesting that seeing each other enhanced participants’ responses, consistent with social facilitation or contagion. Furthermore, interpersonal coordination was higher both for the high-groove and eyes-open conditions, indicating that the social situation of collective music listening affects how music is experienced.
... The profile's smoothness seems to preserve 32 kinematic accuracy (Harris and Wolpert 1998), and have little to do with the effort needed to 33 produce the motion. But effort or energy expenditure appear to affect other aspects of 34 reaching (Huang et al. 2012; Shadmehr et al. 2019), and influence a vast array of other animal 35 behaviors and actions (Alexander 1996). It seems possible that effort or energy do influence the 36 bell-shaped profile, but have gone unrecognized because of incomplete quantification of such 37 ...
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The central nervous system plans human reaching movements with stereotypically smooth kinematic trajectories and fairly consistent durations. Smoothness seems to be explained by accuracy as a primary movement objective, whereas duration seems to avoid excess energy expenditure. But energy does not explain smoothness, so that two aspects of the same movement are governed by seemingly incompatible objectives. Here we show that smoothness is actually economical, because humans expend more metabolic energy for jerkier motions. The proposed mechanism is an underappreciated cost proportional to the rate of muscle force production, for calcium transport to activate muscle. We experimentally tested that energy cost in humans (N=10) performing bimanual reaches cyclically. The empirical cost was then demonstrated to predict smooth, discrete reaches, previously attributed to accuracy alone. A mechanistic, physiologically measurable, energy cost may therefore unify smoothness and duration, and help resolve motor redundancy in reaching movements.
... Therefore, this suggests the participants increased their attention in an effort to increase their accuracy and performance on the second, incentivized test. This is backed by findings that increased saccadic eye movement has been observed upon reward expectation in neuroscience studies [71]. The same can be inferred in the findings of this paper, where the typing test involves vision accuracy, and announcement of a reward therefore increases activation in the O2 sensor. ...
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To understand the impact of incentivized test/retest scenarios – where students are afforded an opportunity to retest for an incentive – in design education settings, this study examines participants brain activity using electroencephalography (EEG) during stressful retest situation. This study mimics educational scenarios where students are afforded an opportunity to retest after a first attempt. Twenty-three student participants were randomly divided into two cohorts: control and experimental. Participants were asked to complete a preliminary questionnaire self-assessing their ability to handle stressful situations. Both cohorts were subsequently asked to complete the typing test and complete an Emotional Stress Reaction Questionnaire (ESRQ), indicating their emotional response during the typing test. The participants were subsequently asked to complete the typing test and accompanying ESRQ a second time. However, prior to the second test, the participants in the experimental cohort were incentivized with a monetary reward for improving their typing speed. This stimulus is used to increase the already stressful situation for the experimental cohort and examine changes in brain activity when the “retest” is incentivized. The results indicate no significant changes in brain activity, emotions, or typing performance for the control group. However, the experimental group showed an increase in EEG sensor activity; specifically, the sensors that control vision and emotion. The experimental group's performance was correlated to their emotional responses, rather than their EEG sensor data. Additionally, the experimental groups' positive emotions were increased for the incentivized typing test. The findings provide recommendations for educational retests practices.
... Research at the cornerstone of decision making and motor control found that individuals can indeed decide to perform a metabolically expensive action if its expected utility (i.e., subjective valuation) was rated as high (Codol et al., 2020;Rigoux & Guigon, 2012). This suggests that motor control reflects the brain's economic evaluation of an action outcome (Shadmehr et al., 2019). ...
Thesis
Human beings constantly adapt the spontaneous pace of their actions in order to interact with their environment. Advances in timing research have shown that two processes (automatic vs. controlled) are involved in the processing of temporal information. There is, nonetheless, a dearth of knowledge regarding the cognitive mechanisms and brain areas underlying the temporal control of motor behaviours. The general aim of my thesis was to examine the cognitive and cerebral resources needed during the execution of actions performed under different time constraints. In Study 1, the involvement of cognitive control in motor timing was investigated using time series analysis and a dual-task paradigm. Results showed that moving fast and slow entailed distinct timing strategies, characterised by contrasting attentional demands. In Study 2, the fNIRS neuroimaging technique was used to examine the cerebral oxygenation of prefrontal and motor areas simultaneously during the execution of upper-limb motor tasks performed under different time constraint. Findings indicated that fast-paced movement relied on greater activity in the motor areas, whereas moving at a close-to-spontaneous pace exerted heavier load on the posterior prefrontal cortex. Study 3 was designed to investigate the ecological validity of motor-timing tasks by providing a direct comparison across the tasks of finger tapping, foot tapping, and stepping on the spot. The results showed that single-limb and whole-body movements entailed distinct timing strategies, and suggested that tapping-to-metronome paradigms might be too far removed from natural behaviours to facilitate translation of the results. Hence, in Study 4, the fNIRS technique was employed to examine prefrontal and motor activation during the execution of upper-limb and whole-body movements under distinct time constraints. Findings indicated that slow pacing led to increased prefrontal activations only during whole-body movements. Yet, a large variability in participants' haemodynamic responses was observed. Therefore, in Study 5, three case studies were conducted to assess the test–retest reliability and define the appropriate number of trials necessary for a block design procedure in fNIRS brain imaging during motor paradigms. The original contribution of the present research programme is that prefrontal cognitive control plays an essential role during the production of slow motor behaviours. Rather than a co-existence of two timing-processes, the present body of work supports an alternative view of motor timing insofar as the production of fast and slow movements relies on a similar motor mechanism. Cognitive monitoring would be additionally involved in the production of slow movements in order to slow the pace of motor execution. This view provides new insights into the cognitive and brain mechanisms underlying adaptative human behaviour.
... This variable was not orthogonal to the others, since it decreased with both stimulus value and response confidence. The link between deliberation time and stimulus value might arise from an appetitive Pavlovian reflex, as suggested in previous studies (Oudiette et al., 2019;Shadmehr et al., 2019), since there was no reason to go faster when valuating better rewards, or slower when valuating worse efforts, in our design. The link between deliberation time and response confidence might relate to the difficulty of the task (Bang and Fleming, 2018;Kiani et al., 2014;Lee and Daunizeau, 2021;Pleskac and Busemeyer, 2010;Ratcliff et al., 2016;Yeung and Summerfield, 2012), i.e. the uncertainty about which rating or choice best reflects subjective . ...
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Deciding about courses of action involves minimizing costs and maximizing benefits. Decision neuroscience studies have implicated both the ventral and dorsal medial prefrontal cortex (vmPFC and dmPFC) in signaling goal value and action cost, but the precise functional role of these regions is still a matter of debate. Here, we suggest a more general functional partition that applies not only to decisions but also to judgments about goal value (expected reward) and action cost (expected effort). In this conceptual framework, cognitive representations related to options (reward value and effort cost) are dissociated from metacognitive representations (confidence and deliberation) related to solving the task (providing a judgment or making a choice). Thus, we used an original approach with the goal of identifying consistencies across several preference tasks, from likeability ratings to binary decisions involving both attribute integration and option comparison. FMRI results confirmed the vmPFC as a generic valuation system, its activity increasing with reward value and decreasing with effort cost. In contrast, more dorsal regions were not concerned with the valuation of options but with metacognitive variables, confidence level being reflected in mPFC activity and deliberation time in dmPFC activity. Thus, there was a dissociation between the effort attached to choice options (represented in the vmPFC) and the effort invested in deliberation (represented in the dmPFC), the latter being expressed in pupil dilation. More generally, assessing commonalities across preference tasks might help reaching a unified view of the neural mechanisms underlying the cost/benefit tradeoffs that drive human behavior.
... Aside from deciding whether to generate a direct or an intermediate response, another important factor governing choices in the face of uncertain options is to weigh the relative desirability of the two options. In particular, prior research has demonstrated that individuals consider both the potential rewards available as well as the likelihood with which those rewards will be successfully attained (for review, see Wolpert and Landy, 2012;Shadmehr et al., 2019). By reward, we mean an exogenous signal (in our case, money) conferred by the experimenter indicating correct behavior; by success likelihood, we mean the probability that the chosen action will be correct and result in an endogenous satisfaction signal. ...
Article
When faced with multiple potential movement options, individuals either reach directly to one of the options, or initiate a reach intermediate between the options. It remains unclear why people generate these two types of behaviors. Using the go-before-you-know task (commonly used to study behavior under choice uncertainty) in humans, we examined two key questions. First, do these two types of responses actually reflect distinct movement strategies? If so, the relative desirability (i.e., weighing the success likelihood vs the attainable reward) of the two target options would not need to be computed identically for direct and intermediate reaches. We showed that indeed, when reward and success likelihood differed between the two options, reach direction was preferentially biased toward different directions for direct versus intermediate reaches. Importantly, this suggests that the computation of subjective values depends on the choice of movement strategy. Second, what drives individual differences in how people respond under uncertainty? We found that risk/reward-seeking individuals tended to generate more intermediate reaches and were more responsive to changes in reward, suggesting these movements may reflect a strategy to maximize reward versus success. Together, these findings suggest that when faced with choice uncertainty, individuals adopt movement strategies consistent with their risk/reward attitude, preferentially biasing behavior toward exogenous rewards or endogenous success and consequently modulating the relative desirability of the available options.
... In addition, 52 when a stimulus is associated with an immediate reward, higher dopaminergic neuron 53 firing usually precedes faster movements [25,26]. Therefore, the kinematics of movements 54 seems to reflect the processes with which the brain temporally discounts rewards, sug- 55 gesting a link between motor as well as valuation processess [20,27,28]. Movements and 56 time share a well-known relation as well: according to Fitts' law [29], the time needed by 57 an individual to move between a starting point and a target point within a given space 58 increases linearly with the difficulty to execute the movement. ...
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Growing evidence suggests that humans and other animals assign value to a stimulus based on its inherent rewarding properties, but also on the costs of the action required to obtain it, such as the cost of time. Here, we examined whether such cost also occurs for mentally simulated actions. Healthy volunteers indicated their subjective value for snack foods while the time to imagine performing the action to obtain the different stimuli was manipulated. In each trial, the picture of one food item and a home position connected through a path were displayed on a computer screen. The path could be either large or thin. Participants first rated the stimulus, and then imagined moving the mouse cursor along the path, from the starting position to the food location. They reported the onset and offset of the imagined movements with a button press. Two main results emerged. First, imagery times were significantly longer for the thin than the large path. Second, participants liked significantly less the snack foods associated with the thin path (i.e., with longer imagery time), possibly because the passage of time strictly associated with action imagery discounts the value of the reward. Importantly, such effects were absent in a control group of participants who performed an identical valuation task, except that no action imagery was required. Our findings hint at the idea that imagined actions, like real actions, carry a cost that affects deeply how people assign value to the stimuli in their environment.
Article
The decision regarding which arm to use to perform a task reflects a complex process that can be influenced by many factors, including effort requirements of acquiring the goal. In this study, we considered a virtual reality environment in which people reached to a visual target in 3D space. To vary the cost of reaching, we altered the visual feedback associated with motion of one arm but not the other. This altered the extent of motion that was required to reach, thus changing the effort required to acquire the goal. We then measured how that change in effort affected the decision regarding which arm to use, as well as the preparation time for the movement that ensued. As expected, with increased visual amplification of one arm (reduced effort to reach the goal), subjects increased the probability of choosing that arm. Surprisingly, however, the reaction times to start these movements were also reduced: despite constancy of the visual representation of the target, reaction times were shorter for movements with less effort. Thus, as the perceived effort associated with accomplishing a goal was reduced for a given limb, the decision-making process was biased toward use of that limb. Furthermore, movements that were perceived to be less effortful were performed with shorter reaction times. These results suggest that visual amplification can alter the perceived effort associated with using a limb, thus increasing frequency of use. This may provide a useful method to increase use of a limb during rehabilitation.
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Besides relying heavily on sensory and reinforcement feedback, motor skill learning may also depend on the level of motivation experienced during training. Yet, how motivation by reward modulates motor learning remains unclear. In 90 healthy subjects, we investigated the net effect of motivation by reward on motor learning while controlling for the sensory and reinforcement feedback received by the participants. Reward improved motor skill learning beyond performance-based reinforcement feedback. Importantly, the beneficial effect of reward involved a specific potentiation of reinforcement-related adjustments in motor commands, which concerned primarily the most relevant motor component for task success and persisted on the following day in the absence of reward. We propose that the long-lasting effects of motivation on motor learning may entail a form of associative learning resulting from the repetitive pairing of the reinforcement feedback and reward during training, a mechanism that may be exploited in future rehabilitation protocols.
Article
The dorsal striatum (dS) has been implicated in storing procedural memories and controlling movement kinematics. Since procedural memories are expressed through movements, the exact nature of the dS function has proven difficult to delineate. Here, we challenged rats in complementary locomotion-based tasks designed to alleviate this confound. Surprisingly, dS lesions did not impair the rats' ability to remember the procedure for the successful completion of motor routines. However, the speed and initiation of the reward-oriented phase of the routines were irreversibly altered by the dS lesion. Further behavioral analyses, combined with modeling in the optimal control framework, indicated that these kinematic alterations were well explained by an increased sensitivity to effort. Our work provides evidence supporting a primary role of the dS in modulating the kinematics of reward-oriented actions, a function that may be related to the optimization of the energetic costs of moving.
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We describe a neural monitor of environmental and physiological resources that informs effort expenditure. Depending on resources and environmental stability, serotonergic and dopaminergic neuromodulations favor different behavioral controls that are organized in corticostriatal loops. This broader perspective produces some suggestions and questions that may not be covered by the foraging approach to vigor of Shadmehr and Ahmed (2020).
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Perceived control—the belief in our ability to successfully influence the environment—significantly shapes how we make decisions and interact with our environment. Because of its intrinsically rewarding nature, the opportunity to exert control tends to bias individuals towards behaviors that endow an enhanced perception of control. Here, we leverage recent behavioral and neuroimaging work to highlight three particular attributes of control (i.e. affective, motivational and protective), which contribute to how perceived control shapes decision making via the corticostriatal circuits and impacts wellbeing. We then consider how impairments in perceived control could represent a transdiagnostic feature across psychopathologies.
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Vigor reflects how motivated people are to respond to stimuli. We previously showed that, on average, humans are more vigorous when a higher rate of reward is available, and that this relationship is modulated by the dopamine precursor levodopa. Dopamine signaling and probabilistic reward learning deteriorate across the adult life span, and thus, the relationship between vigor and reward may also change in aging. We tested this assertion and assessed whether it correlates with D1 dopamine receptor availability, measured using Positron Emission Tomography. We registered response times of 30 older and 30 younger participants during an oddball discrimination task where rewards varied systematically between trials. The average reward rate had a similar impact on vigor in both age groups. There was a weak positive association between ventral striatal dopamine receptor availability and the effect of average reward rate on response time. Overall, the effect of reward on response vigor was similar in younger and older adults, and weakly correlated with dopamine D1 receptor availability.
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Recent theories and data suggest that adapted behavior involves economic computations during which multiple trade-offs between reward value, accuracy requirement, energy expenditure and elapsing time are solved so as to obtain rewards as soon as possible while spending the least possible amount of energy. However, the relative impact of movement energy and duration costs on perceptual decision-making and movement initiation is poorly understood. Here, we tested 31 healthy subjects on a perceptual decision-making task in which they executed reaching movements to report probabilistic choices. In three distinct blocks of trials, the reaching time and energy costs were independently varied while decision difficulty was maintained similar at the block level. Participants also performed a fully instructed delayed-reaching (DR) task in each motor condition. Results in that DR task show that time-consuming movements extended reaction times (RTs) in most subjects, whereas energy-consuming movements led to mixed effects on RTs. In the choice task, about half of the subjects decreased their decision durations (DDs) in the time consuming condition, while the impact of energy costs on DDs were again mixed across subjects. Decision accuracy was overall similar across motor conditions. These results indicate that movement duration and, to a lesser extent, energy expenditure, idiosyncratically affect perceptual decision-making and action initiation. We propose that subjects who shortened their decisions in the time consuming condition of the choice task did so to limit a drop of their rate of reward.
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While it is well established that dopamine transmission is integral in mediating the influence of reward expectations on reward-seeking actions, the precise causal role of dopamine transmission in moment-to-moment cue-driven behavioural control remains contentious. This is a particular issue in situations where it is necessary to refrain from responding to achieve a beneficial outcome. To examine this, we manipulated dopamine transmission pharmacologically as rats performed a Go/No-Go task that required them to either make or withhold action to gain either a small or large reward. Stimulation of D1Rs, both globally and locally in the nucleus accumbens core (NAcC) region consistently disrupted No-Go performance, potentiating inappropriate responses that clustered strongly just after cue presentation. D1R blockade did not, however, improve rats' ability to withhold responses, but instead primarily disrupted performance on Go trials. While global D1R blockade caused a general reduction of invigoration of reward seeking actions, intra-NAcC administration of the D1R antagonist by contrast increased the likelihood that Go trial performance was in an "unfocused" state. Such a state was characterised, both on and off drug, by a reduction in the precision and speed of responding even though the appropriate action sequence was often executed. These findings suggests that the balance of activity at NAcC D1Rs plays a key role in enabling the rapid activation of a focused, reward-seeking state to enable animals to efficiently and accurately achieve their goal.
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Besides relying heavily on sensory and reinforcement feedback, motor skill learning may also depend on the level of motivation experienced during training. Yet, how motivation by reward modulates motor learning remains unclear. In 90 healthy subjects, we investigated the net effect of motivation by reward on motor learning while controlling for the sensory and reinforcement feedback received by the participants. Reward improved motor skill learning beyond performance-based reinforcement feedback. Importantly, the beneficial effect of reward involved a specific potentiation of reinforcement-related adjustments in motor commands, which concerned primarily the most relevant motor component for task success and persisted on the following day in the absence of reward. We propose that the long-lasting effects of motivation on motor learning may entail a form of associative learning resulting from the repetitive pairing of the reinforcement feedback and reward during training, a mechanism that may be exploited in future rehabilitation protocols.
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Due to the close relationship between oculomotor behavior and visual processing, eye movements have been studied in many different areas of research over the last few decades. While these studies have brought interesting insights, specialization within each research area comes at the potential cost of a narrow and isolated view of the oculomotor system. In this review, we want to expand this perspective by looking at the interactions between the two most important types of voluntary eye movements: saccades and pursuit. Recent evidence indicates multiple interactions and shared signals at the behavioral and neurophysiological level for oculomotor control and for visual perception during pursuit and saccades. Oculomotor control seems to be based on shared position- and velocity-related information, which leads to multiple behavioral interactions and synergies. The distinction between position- and velocity-related information seems to be also present at the neurophysiological level. In addition, visual perception seems to be based on shared efferent signals about upcoming eye positions and velocities, which are to some degree independent of the actual oculomotor response. This review suggests an interactive perspective on the oculomotor system, based mainly on different types of sensory input, and less so on separate subsystems for saccadic or pursuit eye movements.
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Value-based decision-making is of central interest in cognitive neuroscience and psychology, as well as in the context of neuropsychiatric disorders characterised by decision-making impairments. Studies examining (neuro-)computational mechanisms underlying choice behaviour typically focus on participants' decisions. However, there is increasing evidence that option valuation might also be reflected in motor response vigour and eye movements, implicit measures of subjective utility. To examine motor response vigour and visual fixation correlates of option valuation in intertemporal choice, we set up a task where the participants selected an option by pressing a grip force transducer, simultaneously tracking fixation shifts between options. As outlined in our preregistration (https://osf.io/k6jct), we used hierarchical Bayesian parameter estimation to model the choices assuming hyperbolic discounting, compared variants of the softmax and drift diffusion model, and assessed the relationship between response vigour and the estimated model parameters. The behavioural data were best explained by a drift diffusion model specifying a non-linear scaling of the drift rate by the subjective value differences. Replicating previous findings, we found a magnitude effect for temporal discounting, such that higher rewards were discounted less. This magnitude effect was further reflected in motor response vigour, such that stronger forces were exerted in the high vs. the low magnitude condition. Bayesian hierarchical linear regression further revealed higher grip forces, faster response times and a lower number of fixation shifts for trials with higher subjective value differences. An exploratory analysis revealed that subjective value sums across options showed an even more pronounced association with trial-wise grip force amplitudes. Our data suggest that subjective utility or implicit valuation is reflected in motor response vigour and visual fixation patterns during intertemporal choice. Taking into account response vigour might thus provide deeper insight into decision-making, reward valuation and maladaptive changes in these processes, e.g. in the context of neuropsychiatric disorders.
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Reward can improve motor learning and the consolidation of motor memories. Identifying the features of reward feedback that are critical for motor learning is a necessary step for successful integration into rehabilitation programs. One central feature of reward feedback that may affect motor learning is its timing, that is, the delay after which reward is delivered following movement execution. In fact, research on associative learning has shown that short and long reward delays (e.g., 1 and 6 s following action execution) activate preferentially the striatum and the hippocampus, respectively, which both contribute with varying degrees to motor learning. Given the distinct functional role of these two areas, we hypothesized that reward timing could modulate how people learn and consolidate a new motor skill. In sixty healthy participants, we found that delaying reward delivery by a few seconds influenced motor learning dynamics. Indeed, training with a short reward delay (i.e., 1 s) induced slow, yet continuous gains in performance, while a long reward delay (i.e., 6 s) led to initially high learning rates that were followed by an early plateau in the learning curve and a lower endpoint performance. Moreover, participants who successfully learned the skill with a short reward delay displayed overnight consolidation, while those who trained with a long reward delay exhibited an impairment in the consolidation of the motor memory. Overall, our data show that reward timing affects motor learning, potentially by modulating the engagement of different learning processes, a finding that could be exploited in future rehabilitation programs.
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Understanding the behavior of primates is important for primatology, for psychology, and for biology more broadly. It is also important for biomedicine, where primates are an important model organism, and whose behavior is often an important variable of interest. Our ability to rigorously quantify behavior has, however, long been limited. On one hand, we can rigorously quantify low-information measures like preference, looking time, and reaction time; on the other, we can use more gestalt measures like behavioral categories tracked via ethogram, but at high cost and with high variability. Recent technological advances have led to a major revolution in behavioral measurement that offers affordable and scalable rigor. Specifically, digital video cameras and automated pose tracking software can provide measures of full-body position (i.e., pose) of primates over time (i.e., behavior) with high spatial and temporal resolution. Pose-tracking technology in turn can be used to infer behavioral states, such as eating, sleeping, and mating. We call this technological approach behavioral imaging. In this review, we situate the behavioral imaging revolution in the history of the study of behavior, argue for investment in and development of analytical and research techniques that can profit from the advent of the era of big behavior, and propose that primate centers and zoos will take on a more central role in relevant fields of research than they have in the past. Research highlights • Recent advances in technology permit the automated tracking of primates. • Automated tracking promises several benefits to biology and biomedicine. • Zoos and primate centers are likely to be more important in the era of behavioral tracking.
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Assessing the cognitive impact of user interfaces is a shared focus of human-computer interaction researchers and cognitive scientists. Methods of cognitive assessment based on data derived from the system itself, rather than external apparatus, have the potential to be applied in a range of scenarios. The current study applied methods of analyzing kinematics to mouse movements in a computer-based task, alongside the detection response task, a standard workload measure. Sixty-five participants completed a task in which stationary stimuli were tar;geted using a mouse, with a within-subjects factor of task workload based on the number of targets to be hovered over with the mouse (one/two), and a between-subjects factor based on whether both targets (exhaustive) or just one target (minimum-time) needed to be hovered over to complete a trial when two targets were presented. Mouse movement onset times were slower and mouse movement trajectories exhibited more submovements when two targets were presented, than when one target was presented. Responses to the detection response task were also slower in this condition, indicating higher cognitive workload. However, these differences were only found for participants in the exhaustive condition, suggesting those in the minimum-time condition were not affected by the presence of the second target. Mouse movement trajectory results agreed with other measures of workload and task performance. Our findings suggest this analysis can be applied to workload assessments in real-world scenarios.
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The simple task of walking up a sidewalk curb is actually a dynamic prediction task. The curb is a disturbance that could cause a loss of momentum if not anticipated and compensated for. It might be possible to adjust momentum sufficiently to ensure undisturbed time of arrival, but there are infinite possible ways to do so. Much of steady, level gait is determined by energy economy, which should be at least as important with terrain disturbances. It is, however, unknown whether economy also governs walking up a curb, and whether anticipation helps. Here we show that humans compensate with an anticipatory pattern of forward speed adjustments, predicted by a criterion of minimizing mechanical energy input. The strategy is mechanistically predicted by optimal control for a simple model of bipedal walking dynamics, with each leg's push-off work as input. Optimization predicts a tri-phasic trajectory of speed (and thus momentum) adjustments, including an anticipatory phase. In experiment, human subjects ascend an artificial curb with the predicted tri-phasic trajectory, which approximately conserves overall walking speed relative to undisturbed flat ground. The trajectory involves speeding up in a few steps before the curb, losing considerable momentum from ascending it, and then regaining speed in a few steps thereafter. Descending the curb entails a nearly opposite, but still anticipatory, speed fluctuation trajectory, in agreement with model predictions that speed fluctuation amplitudes should scale linearly with curb height. The fluctuation amplitudes also decrease slightly with faster average speeds, also as predicted by model. Humans can reason about the dynamics of walking to plan anticipatory and economical control, even with a sidewalk curb in the way.
Article
Brain-computer interfaces (BCIs) for movement restoration typically decode the user's intent from neural activity in their primary motor cortex (M1) and use this information to enable 'mental control' of an external device. Here, we argue that activity in M1 has both too little and too much information for optimal decoding: too little, in that many regions beyond it contribute unique motor outputs and have movement-related information that is absent or otherwise difficult to resolve from M1 activity; and too much, in that motor commands are tangled up with nonmotor processes such as attention and feedback processing, potentially hindering decoding. Both challenges might be circumvented, we argue, by integrating additional information from multiple brain regions to develop BCIs that will better interpret the user's intent.
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In general, speed-accuracy tradeoff adjustments in decision-making have been studied separately from those in motor control. In the wild however, animals coordinate their decision and action, freely investing time in choosing versus moving given specific contexts. Recent behavioral studies support this view, indicating that humans can trade decision time for movement time to maximize their reward rate at the level of entire experimental sessions. Besides, it is established that choice outcomes largely impact subsequent decisions. Crucially though, whether and how a decision also influences the subsequent motor behavior, and whether and how a motor error influences the next decision is currently unknown. Here we address these questions by analyzing trial-to-trial changes of choice and motor behaviors in humans instructed to perform successive perceptual decisions expressed with reaching movement whose duration was either bounded or unconstrained in separate tasks. Results indicate that after a bad decision, subjects who were not constrained in their action duration decided more slowly and more accurately. Interestingly, they also shortened their subsequent movement duration by moving faster. Conversely, we found that movement errors not only influenced the speed and the accuracy of the following movement, but those of the decision as well. If the movement had to be slowed down, the decision that precedes that movement was accelerated, and vice versa. Together, these results indicate that from one trial to the next, humans are primarily concerned about determining a behavioral duration as a whole instead of optimizing each of the decision and action speed-accuracy trade-offs independently of each other.
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Researchers in the field of active perception study how sensory processes coalesce with motor actions to extract information from the world. Such actions intrinsically alter perceptual processing and have intended sensory outcomes, but also lead to incidental sensory consequences, which are side effects of moving the sensory surface to its intended goal. These incidental consequences of actions are generally considered a nuisance to perception that needs to be attenuated or suppressed during movement execution. In this Perspective, we propose instead that incidental sensory consequences of actions shape perceptual processes through action–perception couplings and we review evidence from the domain of active vision. We propose four hallmarks representing the degrees to which actions are an integral part of a perceptual processing architecture. Finally, we outline a research strategy for probing these hallmarks in active perceptual systems and conclude that researchers of perception should embrace the study of action kinematics in pursuit of their questions. Studying action is key for understanding perception because perceptual processes are shaped by movements of the sensory surface. In this Perspective, Rolfs and Schweitzer propose four hallmarks of action–perception coupling and outline a research strategy for the study of action kinematics in perception.
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How the brain determines the vigor of goal-directed movements is a fundamental question in neuroscience. Recent evidence has suggested that vigor results from a trade-off between a cost related to movement production (cost of movement) and a cost related to our brain's tendency to temporally discount the value of future reward (cost of time). However, whether it is critical to hypothesize a cost of time to explain the vigor of basic reaching movements with intangible reward is unclear because the cost of movement may be theoretically sufficient for this purpose. Here we directly address this issue by designing an isometric reaching task whose completion can be accurate and effortless in prefixed durations. The cost of time hypothesis predicts that participants should be prone to spend energy to save time even if the task can be accomplished at virtually no motor cost. Accordingly, we found that all participants generated substantial amounts of force to invigorate task accomplishment, especially when the prefixed duration was long enough. Remarkably, the time saved by each participant was linked to their original vigor in the task and predicted by an optimal control model balancing out movement and time costs. Taken together, these results supports the existence of an idiosyncratic, cognitive cost of time that underlies the invigoration of basic isometric reaching movements.
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The cerebellum has long been proposed to play a role in cognitive function, although this has remained controversial. This idea has received renewed support with the recent discovery that signals associated with reward can be observed in the cerebellar circuitry, particularly in goal-directed learning tasks involving an interplay between the cerebellar cortex, basal ganglia, and cerebral cortex. Remarkably, a wide range of reward contingencies—including reward expectation, delivery, size, and omission—can be encoded by specific circuit elements in a manner that reflects the microzonal organization of the cerebellar cortex. The facts that reward signals have been observed in both the mossy fiber and climbing fiber input pathways to the cerebellar cortex and that their convergence may trigger plasticity in Purkinje cells suggest that these interactions may be crucial for the role of the cerebellar cortex in learned behavior. These findings strengthen the emerging consensus that the cerebellum plays a pivotal role in shaping cognitive processing and suggest that the cerebellum may combine both supervised learning and reinforcement learning to optimize goal-directed action. We make specific predictions about how cerebellar circuits can work in concert with the basal ganglia to guide different stages of learning.
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In decision neuroscience, the motor system has primarily been associated with executing choice actions. However, a competing perspective suggests its engagement in the evaluation of options, traditionally considered to be performed by the brain's valuation system. Here, we investigate the role of the motor system in value-based decision making by determining the neural circuitries associated with the sensorimotor beta oscillations previously identified to encode decision options. In a simultaneous EEG-fMRI study, participants evaluated reward and risk associated with a forthcoming action. A significant sensorimotor beta desynchronization was identified prior to and independent of response. The level of beta desynchronization showed evidence of encoding the reward levels. This beta desynchronization covaried, on a trial-by-trial level, with BOLD activity in the cortico-basal ganglia-thalamic circuitry. In contrast, there was only a weak covariation within the valuation network, despite significant modulation of its BOLD activity by reward levels. These results suggest that the way in which decision variables are processed differs in the valuation network and in the cortico-basal ganglia-thalamic circuitry. We propose that sensorimotor beta oscillations indicate incentive motivational drive towards a choice action computed from the decision variables even prior to making a response, and it arises from the cortico-basal ganglia-thalamic circuitry.
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In science, as in life, one can only hope to both inform others, and be informed by them. The commentaries associated with our book Vigor have highlighted the many ways in which the theory that we proposed can be improved. For example, there are a myriad of factors that need to be considered in a fully encompassing objective function. The neural mechanisms underlying the links between movement and decision-making have yet to be unraveled. The implications of a two-way interaction between movement and decisions at both the individual and social levels remain to be understood. The commentaries outline future questions, and encouragingly highlight the diversity of science communities that may be linked via the concept of vigor.
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Saccadic peak velocity increases in a stereotyped manner with the amplitude of eye movements. This relationship, known as the main sequence, has classically been considered to be fixed, although several recent studies have demonstrated that velocity can be modulated to some extent by external incentives. However, the ability to voluntarily control saccadic velocity and its association with motivation has yet to be investigated. Here, in three separate experimental paradigms, we measured the effects of incentivisation on saccadic velocity, reaction time and preparatory pupillary changes in 53 young healthy participants. In addition, the ability to voluntarily modulate saccadic velocity with and without incentivisation was assessed. Participants varied in their ability to increase and decrease the velocity of their saccades when instructed to do so. This effect correlated with motivation level across participants, and was further modulated by addition of monetary reward and avoidance of loss. The findings show that a degree of voluntary control of saccadic velocity is possible in some individuals, and that the ability to modulate peak velocity is associated with intrinsic levels of motivation.
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A perceptual judgment is typically characterized by constructing psychometric and chrono-metric functions, i.e., by mapping the accuracies and reaction times of motor choices as functions of a sensory stimulus feature dimension. Here, we show that various saccade metrics (e.g., peak velocity) are similarly modulated as functions of sensory cue viewing time during performance of an urgent-decision task. Each of the newly discovered functions reveals the dynamics of the perceptual evaluation process inherent to the underlying judgment. Remarkably, saccade peak velocity correlates with statistical decision confidence, suggesting that saccade kinematics reflect the degree of certainty with which an urgent perceptual decision is made. The data were explained by a race-to-threshold model that also replicates standard performance measures and cortical oculomotor neuronal activity in the task. The results indicate that, although largely stereotyped, saccade metrics carry subtle but reliable traces of the underlying cognitive processes that give rise to each oculomotor choice.
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People usually move at a self-selected pace in everyday life. Yet, the principles underlying the formation of human movement vigour remain unclear, particularly in view of intriguing inter-individual variability. It has been hypothesized that how the brain values time may be the cornerstone of such differences, beyond biomechanics. Here, we focused on the vigour of self-paced reaching movement and assessed the stability of vigour via repeated measurements within participants. We used an optimal control methodology to identify a cost of time (CoT) function underlying each participant's vigour, considering a model of the biomechanical cost of movement. We then tested the extent to which anthropometric or psychological traits, namely boredom proneness and impulsivity, could account for a significant part of inter-individual variance in vigour and CoT parameters. Our findings show that the vigour of reaching is largely idiosyncratic and tend to corroborate a relation between the relative steepness of the identified CoT and boredom proneness, a psychological trait relevant to one's relationship with time in decision-making.
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Deciding when and whether to move is critical for survival. Loss of dopamine neurons (DANs) of the substantia nigra pars compacta (SNc) in patients with Parkinson’s disease causes deficits in movement initiation and slowness of movement¹. The role of DANs in self-paced movement has mostly been attributed to their tonic activity, whereas phasic changes in DAN activity have been linked to reward prediction2,3. This model has recently been challenged by studies showing transient changes in DAN activity before or during self-paced movement initiation4,5,6,7. Nevertheless, the necessity of this activity for spontaneous movement initiation has not been demonstrated, nor has its relation to initiation versus ongoing movement been described. Here we show that a large proportion of SNc DANs, which did not overlap with reward-responsive DANs, transiently increased their activity before self-paced movement initiation in mice. This activity was not action-specific, and was related to the vigour of future movements. Inhibition of DANs when mice were immobile reduced the probability and vigour of future movements. Conversely, brief activation of DANs when mice were immobile increased the probability and vigour of future movements. Manipulations of dopamine activity after movement initiation did not affect ongoing movements. Similar findings were observed for the initiation and execution of learned action sequences. These findings causally implicate DAN activity before movement initiation in the probability and vigour of future movements.
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Two basic trade-offs interact while our brain decides how to move our body. First, with the cost-benefit trade-off, the brain trades between the importance of moving faster toward a target that is more rewarding and the increased muscular cost resulting from a faster movement. Second, with the speed-accuracy trade-off, the brain trades between how accurate the movement needs to be and the time it takes to achieve such accuracy. So far, these two trade-offs have been well studied in isolation, despite their obvious interdependence. To overcome this limitation, we propose a new model that is able to simultaneously account for both trade-offs. The model assumes that the central nervous system maximizes the expected utility resulting from the potential reward and the cost over the repetition of many movements, taking into account the probability to miss the target. The resulting model is able to account for both the speed-accuracy and the cost-benefit trade-offs. To validate the proposed hypothesis, we confront the properties of the computational model to data from an experimental study where subjects have to reach for targets by performing arm movements in a horizontal plane. The results qualitatively show that the proposed model successfully accounts for both cost-benefit and speed-accuracy trade-offs.
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Human eye movements are stereotyped and repeatable, but how specific to a normal individual are the quantitative properties of his or her eye movements? We recorded saccades, anti-saccades and smooth-pursuit eye movements in a sample of over 1000 healthy young adults. A randomly selected subsample (10%) of participants were re-tested on a second occasion after a median interval of 18.8 days, allowing us to estimate reliabilities. Each of several derived measures, including latencies, accuracies, velocities, and left-right asymmetries, proved to be very reliable. We give normative means and distributions for each measure and describe the pattern of correlations amongst them. We identify several measures that exhibit significant sex differences. The profile of our oculomotor measures for an individual constitutes a personal oculomotor signature that distinguishes that individual from most other members of the sample of 1000.
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For goal-directed behaviour it is critical that we can both select the appropriate action and learn to modify the underlying movements (for example, the pitch of a note or velocity of a reach) to improve outcomes. The basal ganglia are a critical nexus where circuits necessary for the production of behaviour, such as the neocortex and thalamus, are integrated with reward signalling to reinforce successful, purposive actions. The dorsal striatum, a major input structure of basal ganglia, is composed of two opponent pathways, direct and indirect, thought to select actions that elicit positive outcomes and suppress actions that do not, respectively. Activity-dependent plasticity modulated by reward is thought to be sufficient for selecting actions in the striatum. Although perturbations of basal ganglia function produce profound changes in movement, it remains unknown whether activity-dependent plasticity is sufficient to produce learned changes in movement kinematics, such as velocity. Here we use cell-type-specific stimulation in mice delivered in closed loop during movement to demonstrate that activity in either the direct or indirect pathway is sufficient to produce specific and sustained increases or decreases in velocity, without affecting action selection or motivation. These behavioural changes were a form of learning that accumulated over trials, persisted after the cessation of stimulation, and were abolished in the presence of dopamine antagonists. Our results reveal that the direct and indirect pathways can each bidirectionally control movement velocity, demonstrating unprecedented specificity and flexibility in the control of volition by the basal ganglia.
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Previous research shows that human eye movements can serve as a valuable source of information about the structural elements of the oculomotor system and they also can open a window to the neural functions and cognitive mechanisms related to visual attention and perception. The research field of eye movement-driven biometrics explores the extraction of individual-specific characteristics from eye movements and their employment for recognition purposes. In this work, we present a study for the incorporation of dynamic saccadic features into a model of eye movement-driven biometrics. We show that when these features are added to our previous biometric framework and tested on a large database of 322 subjects, the biometric accuracy presents a relative improvement in the range of 31.6-33.5% for the verification scenario, and in range of 22.3-53.1% for the identification scenario. More importantly, this improvement is demonstrated for different types of visual stimulus (random dot, text, video), indicating the enhanced robustness offered by the incorporation of saccadic vigor and acceleration cues.
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Progressive depletion of midbrain dopamine neurons (PDD) is associated with deficits in the initiation, speed, and fluidity of voluntary movement. Models of basal ganglia function focus on initiation deficits; however, it is unclear how they account for deficits in the speed or amplitude of movement (vigor). Using an effort-based operant conditioning task for head-fixed mice, we discovered distinct functional classes of neurons in the dorsal striatum that represent movement vigor. Mice with PDD exhibited a progressive reduction in vigor, along with a selective impairment of its neural representation in striatum. Restoration of dopaminergic tone with a synthetic precursor ameliorated deficits in movement vigor and its neural representation, while suppression of striatal activity during movement was sufficient to reduce vigor. Thus, dopaminergic input to the dorsal striatum is indispensable for the emergence of striatal activity that mediates adaptive changes in movement vigor. These results suggest refined intervention strategies for Parkinson's disease.
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Speed-accuracy trade-off is an intensively studied law governing almost all behavioral tasks across species. Here we show that motivation by reward breaks this law, by simultaneously invigorating movement and improving response precision. We devised a model to explain this paradoxical effect of reward by considering a new factor: the cost of control. Exerting control to improve response precision might itself come at a cost-a cost to attenuate a proportion of intrinsic neural noise. Applying a noise-reduction cost to optimal motor control predicted that reward can increase both velocity and accuracy. Similarly, application to decision-making predicted that reward reduces reaction times and errors in cognitive control. We used a novel saccadic distraction task to quantify the speed and accuracy of both movements and decisions under varying reward. Both faster speeds and smaller errors were observed with higher incentives, with the results best fitted by a model including a precision cost. Recent theories consider dopamine to be a key neuromodulator in mediating motivational effects of reward. We therefore examined how Parkinson's disease (PD), a condition associated with dopamine depletion, alters the effects of reward. Individuals with PD showed reduced reward sensitivity in their speed and accuracy, consistent in our model with higher noise-control costs. Including a cost of control over noise explains how reward may allow apparent performance limits to be surpassed. On this view, the pattern of reduced reward sensitivity in PD patients can specifically be accounted for by a higher cost for controlling noise. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
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Speed-accuracy tradeoffs (SATs) exist in both decision-making and movement control, and are generally studied separately. However, in natural behavior animals are free to adjust the time invested in deciding and moving so as to maximize their reward rate. Here, we investigate whether shared mechanisms exist for SAT adjustment in both decisions and actions. Two monkeys performed a reach decision task in which they watched 15 tokens jump, one every 200 ms, from a central circle to one of two peripheral targets, and had to guess which target would ultimately receive the majority of tokens. The monkeys could decide at any time, and once a target was reached, the remaining token movements accelerated to either 50 ms ("fast" block) or 150 ms ("slow" block). Decisions were generally earlier and less accurate in fast than slow blocks, and in both blocks, the criterion of accuracy decreased over time within each trial. This could be explained by a simple model in which sensory information is combined with a linearly growing urgency signal. Remarkably, the duration of the reaching movements produced after the decision decreased over time in a similar block-dependent manner as the criterion of accuracy estimated by the model. This suggests that SATs for deciding and acting are influenced by a shared urgency/vigor signal. Consistent with this, we observed that the vigor of saccades performed during the decision process was higher in fast than in slow blocks, suggesting the influence of a context-dependent global arousal. Copyright © 2014 the authors 0270-6474/14/3416442-13$15.00/0.
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If we assume that the purpose of a movement is to acquire a rewarding state, the duration of the movement carries a cost because it delays acquisition of reward. For some people, passage of time carries a greater cost, as evidenced by how long they are willing to wait for a rewarding outcome. These steep discounters are considered impulsive. Is there a relationship between cost of time in decision making and cost of time in control of movements? Our theory predicts that people who are more impulsive should in general move faster than subjects who are less impulsive. To test our idea, we considered elementary voluntary movements: saccades of the eye. We found that in humans, saccadic vigor, assessed using velocity as a function of amplitude, was as much as 50% greater in one subject than another; that is, some people consistently moved their eyes with high vigor. We measured the cost of time in a decision-making task in which the same subjects were given a choice between smaller odds of success immediately and better odds if they waited. We measured how long they were willing to wait to obtain the better odds and how much they increased their wait period after they failed. We found that people that exhibited greater vigor in their movements tended to have a steep temporal discount function, as evidenced by their waiting patterns in the decision-making task. The cost of time may be shared between decision making and motor control.
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Animals are thought to evaluate the desirability of action options using a unified scale that combines predicted benefits ("rewards"), costs, and the animal's internal motivational state. Midbrain dopamine neurons have long been associated with the reward part of this equation, but it is unclear whether these neurons also estimate the costs of taking an action. We studied the spiking activity of dopamine neurons in the substantia nigra pars compacta of monkeys (Macaca mulatta) during a reaching task in which the energetic costs incurred (friction loads) and the benefits gained (drops of food) were manipulated independently. Although the majority of dopamine neurons encoded the upcoming reward alone, a subset predicted net utility of a course of action by signaling the expected reward magnitude discounted by the invested cost in terms of physical effort. In addition, the tonic activity of some dopamine neurons was slowly reduced in conjunction with the accumulated trials, which is consistent with the hypothesized role for tonic dopamine in the invigoration or motivation of instrumental responding. The present results shed light on an often-hypothesized role for dopamine in the regulation of the balance in natural behaviors between the energy expended and the benefits gained, which could explain why dopamine disorders, such as Parkinson's disease, lead to a breakdown of that balance.
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Our gaze tends to be directed to objects previously associated with rewards. Such object values change flexibly or remain stable. Here we present evidence that the monkey substantia nigra pars reticulata (SNr) in the basal ganglia represents stable, rather than flexible, object values. After across-day learning of object-reward association, SNr neurons gradually showed a response bias to surprisingly many visual objects: inhibition to high-valued objects and excitation to low-valued objects. Many of these neurons were shown to project to the ipsilateral superior colliculus. This neuronal bias remained intact even after >100 d without further learning. In parallel with the neuronal bias, the monkeys tended to look at high-valued objects. The neuronal and behavioral biases were present even if no value was associated during testing. These results suggest that SNr neurons bias the gaze toward objects that were consistently associated with high values in one's history.
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Author Summary Behavior is made of decisions and actions. The decisions are based on the costs and benefits of potential actions, and the chosen actions are executed through the proper control of body segments. The corresponding processes are generally considered in separate theories of decision making and motor control, which cannot explain how the actual costs and benefits of a chosen action can be consistent with the expected costs and benefits involved at the decision stage. Here, we propose an overarching optimal model of decision and motor control based on the maximization of a mixed function of costs and benefits. The model provides a unified account of decision in cost/benefit situations (e.g. choice between small reward/low effort and large reward/high effort options), and motor control in realistic motor tasks. The model appears suitable to advance our understanding of the neural bases and pathological aspects of decision making and motor control.
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Background: Lower ambulatory performance with aging may be related to a reduced oxidative capacity within skeletal muscle. This study examined the associations between skeletal muscle mitochondrial capacity and efficiency with walking performance in a group of older adults. Methods: Thirty-seven older adults (mean age 78 years; 21 men and 16 women) completed an aerobic capacity (VO2 peak) test and measurement of preferred walking speed over 400 m. Maximal coupled (State 3; St3) mitochondrial respiration was determined by high-resolution respirometry in saponin-permeabilized myofibers obtained from percutanous biopsies of vastus lateralis (n = 22). Maximal phosphorylation capacity (ATPmax) of vastus lateralis was determined in vivo by (31)P magnetic resonance spectroscopy (n = 30). Quadriceps contractile volume was determined by magnetic resonance imaging. Mitochondrial efficiency (max ATP production/max O2 consumption) was characterized using ATPmax per St3 respiration (ATPmax/St3). Results: In vitro St3 respiration was significantly correlated with in vivo ATPmax (r (2) = .47, p = .004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO2 peak (r (2) = .33, p = .006). ATPmax (r (2) = .158, p = .03) and VO2 peak (r (2) = .475, p < .0001) were correlated with preferred walking speed. Inclusion of both ATPmax/St3 and VO2 peak in a multiple linear regression model improved the prediction of preferred walking speed (r (2) = .647, p < .0001), suggesting that mitochondrial efficiency is an important determinant for preferred walking speed. Conclusions: Lower mitochondrial capacity and efficiency were both associated with slower walking speed within a group of older participants with a wide range of function. In addition to aerobic capacity, lower mitochondrial capacity and efficiency likely play roles in slowing gait speed with age.
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OPTIMAL foraging theory is based on the assumption that natural selection favours animals that forage most efficiently1-3. But such selection does not act directly on foraging efficiency, but rather indirectly by favouring animals that survive and reproduce most successfully. Studies that use optimal foraging models often assume that maximization of some behavioural currency, such as the animal's net rate of energy gain, maximizes the animal's fitness4, but rarely is an attempt made to test this assumption5-8. Most studies of the effects of foraging behaviour on fitness fail to control for the amount of energy gained by the foraging animals5-8, and lead to the obvious conclusion that animals that eat more reproduce more. Often the studies do not control for characters correlated with foraging behaviour6 or compare traits assumed to be correlated with fitness7,8. A better method would be to assign net rates of energy gain to randomly chosen individuals for their entire lifetimes in a controlled environment and measure fitness directly. Variation in the amount of energy consumed would be controlled by using individuals that employ a time-minimizing foraging strategy9 and would alter the time taken to satisfy their daily energy requirements, while obtaining the same absolute amount of energy. I have now manipulated the net rate of energy gain in four populations of the zebra finch Taeniopygia guttata, and show that fitness, as measured by population growth rate, is indeed positively and significantly correlated with the net rate of energy gain.
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Preferences for different combinations of costs and benefits are a key source of variability in economic decision-making. However, the neurochemical basis of individual differences in these preferences is poorly understood. Studies in both animals and humans have demonstrated that direct manipulation of the neurotransmitter dopamine (DA) significantly impacts cost/benefit decision-making, but less is known about how naturally occurring variation in DA systems may relate to individual differences in economic behavior. In the present study, 25 healthy volunteers completed a dual-scan PET imaging protocol with [(18)F]fallypride and d-amphetamine to measure DA responsivity and separately completed the effort expenditure for rewards task, a behavioral measure of cost/benefit decision-making in humans. We found that individual differences in DA function in the left striatum and ventromedial prefrontal cortex were correlated with a willingness to expend greater effort for larger rewards, particularly when probability of reward receipt was low. Additionally, variability in DA responses in the bilateral insula was negatively correlated with willingness to expend effort for rewards, consistent with evidence implicating this region in the processing of response costs. These findings highlight the role of DA signaling in striatal, prefrontal, and insular regions as key neurochemical mechanisms underlying individual differences in cost/benefit decision-making.
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We recorded neuronal activity in the supplementary eye field (SEF) while monkeys made saccades to targets that yielded rewards of variable amount and uncertainty of delivery. Some SEF cells (29%) represented the anticipated value of the saccade target. These neurons encoded the value of the reward option but did not reflect the action necessary to obtain the reward. A plurality of cells (45%) represented both saccade direction and value. These neurons reflect action value, i.e., the value that is expected to follow from a specific saccade. Other cells (13%) represented only saccade direction. The SEF neurons matched the monkey's risk-seeking behavior by responding more strongly to the uncertain reward options than would be expected based on their response to the sure options and the cued outcome probability. Thus SEF neurons represented subjective, not expected, value. Across the SEF population, option-value signals developed early, ∼120 ms prior to saccade execution. Action-value and saccade direction signals developed ∼60 ms later. These results suggest that the SEF is involved in transforming option-value signals into action-value signals. However, in contrast to other oculomotor neurons, SEF neurons did not reach a constant level of activity before saccade onset. Instead the activity level of many (52%) SEF neurons still reflected value at the time just before saccade initiation. This suggests that SEF neurons guide the selection of a saccade based on value information but do not participate in the initiation of that saccade.
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During foraging, animals decide how long to stay at a patch and harvest reward, and then, they move with certain vigor to another location. How does the brain decide when to leave, and how does it determine the speed of the ensuing movement? Here, we considered the possibility that both the decision-making and the motor control problems aimed to maximize a single normative utility: the sum of all rewards acquired minus all efforts expended divided by total time. This optimization could be achieved if the brain compared a local measure of utility with its history. To test the theory, we examined behavior of people as they gazed at images: they chose how long to look at the image (harvesting information) and then moved their eyes to another image, controlling saccade speed. We varied reward via image content and effort via image eccentricity, and then, we measured how these changes affected decision making (gaze duration) and motor control (saccade speed). After a history of low rewards, people increased gaze duration and decreased saccade speed. In anticipation of future effort, they lowered saccade speed and increased gaze duration. After a history of high effort, they elevated their saccade speed and increased gaze duration. Therefore, the theory presented a principled way with which the brain may control two aspects of behavior: movement speed and harvest duration. Our experiments confirmed many (but not all) of the predictions, suggesting that harvest duration and movement speed, fundamental aspects of behavior during foraging, may be governed by a shared principle of control.
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Humans naturally select several parameters within a gait that correspond with minimizing metabolic cost. Much less is understood about the role of metabolic cost in selecting between gaits. Here, we asked participants to decide between walking or running out and back to different gait specific markers. The distance of the walking marker was adjusted after each decision to identify relative distances where individuals switched gait preferences. We found that neither minimizing solely metabolic energy nor minimizing solely movement time could predict how the group decided between gaits. Of our twenty participants, six behaved in a way that tended towards minimizing metabolic energy, while eight favoured strategies that tended more towards minimizing movement time. The remaining six participants could not be explained by minimizing a single cost. We provide evidence that humans consider not just a single movement cost, but instead a weighted combination of these conflicting costs with their relative contributions varying across participants. Individuals who placed a higher relative value on time ran faster than individuals who placed a higher relative value on metabolic energy. Sensitivity to temporal costs also explained variability in an individual's preferred velocity as a function of increasing running distance. Interestingly, these differences in velocity both within and across participants were absent in walking, possibly due to a steeper metabolic cost of transport curve. We conclude that metabolic cost plays an essential, but not exclusive role in gait decisions.
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A common aspect of individuality is our subjective preferences in evaluation of reward and effort. The neural circuits that evaluate these commodities influence circuits that control our movements, raising the possibility that vigor differences between individuals may also be a trait of individuality, reflecting a willingness to expend effort. In contrast, classic theories in motor-control suggest that vigor differences reflect a speed-accuracy trade-off, predicting that those who move fast are sacrificing accuracy for speed. Here we tested these contrasting hypotheses. We measured motion of the eyes, head, and arm in healthy humans during various elementary movements (saccades, head-free gaze shifts, and reaching). For each person we characterized their vigor, i.e., the speed with which they moved a body part (peak velocity) with respect to the population mean. Some moved with low vigor, while others moved with high vigor. Those with high vigor tended to react sooner to a visual stimulus, moving both their eyes and arm with a shorter reaction-time. Arm and head vigor were tightly linked: individuals who moved their head with high vigor also moved their arm with high vigor. However, eye vigor did not correspond strongly with arm or head vigor. In all modalities, vigor had no impact on endpoint accuracy, demonstrating that differences in vigor were not due to a speed-accuracy tradeoff. Our results suggest that movement vigor may be a trait of individuality, not reflecting a willingness to accept inaccuracy, but demonstrating a propensity to expend effort.
Article
Making a movement may be thought of as an economic decision in which one spends effort in order to acquire reward. Time discounts reward, which predicts that the magnitude of reward should affect movement vigor: we should move faster, spending greater effort, when there is greater reward at stake. Indeed, saccade peak velocities are greater and reaction-times are shorter when a target is paired with reward. Here, we focused on human reaching and asked whether movement kinematics were affected by expectation of reward. Participants made out-and-back reaching movements to one of four quadrants of a 14cm circle. During various periods of the experiment only one of the four quadrants was paired with reward, and the transition from reward to non-reward status of a quadrant occurred randomly. Our experiment design minimized dependence of reward on accuracy, granting the subjects wide latitude in self-selecting their movement speed, amplitude, and variability. When a quadrant was paired with reward, reaching movements had a shorter reaction-time, higher peak velocity, and greater amplitude. Despite this greater vigor, movements toward the rewarded quadrant suffered from less variability: both reaction-times and reach kinematics were less variable when there was expectation of reward. Importantly, the effect of reward on vigor was specific to the movement component that preceded the time of reward (outward reach), not the movement component that followed it (return reach). Our results suggest that expectation of reward not only increases vigor of human reaching, but also decreases its variability.
Article
Prominent theories of decision making suggest that the basal ganglia (BG) play a causal role in deliberation between action choices. An alternative hypothesis is that deliberation occurs in cortical regions, while the BG control the speed-accuracy trade-off (SAT) between committing to a choice versus continuing to deliberate. Here, we test these hypotheses by recording activity in the internal and external segments of the globus pallidus (GPi/GPe) while monkeys perform a task dissociating the process of deliberation, the moment of commitment, and adjustment of the SAT. Our data suggest that unlike premotor and motor cortical regions, pallidal output does not contribute to the process of deliberation but instead provides a time-varying signal that controls the SAT and reflects the growing urgency to commit to a choice. Once a target is selected by cortical regions, GP activity confirms commitment to the decision and invigorates the subsequent movement.
Article
Given two rewarding stimuli, animals tend to choose the more rewarding (or less effortful) option. However, they also move faster toward that stimulus [1-5]. This suggests that reward and effort not only affect decision-making, they also influence motor control [6, 7]. How does the brain compute the effort requirements of a task? Here, we considered data acquired during walking, reaching, flying, or isometric force production. In analyzing the decision-making and motor-control behaviors of various animals, we considered the possibility that the brain may estimate effort objectively, via the metabolic energy consumed to produce the action. We measured the energetic cost of reaching and found that, like walking, it was convex in time, with a global minimum, implying that there existed a movement speed that minimized effort. However, reward made it worthwhile to be energetically inefficient. Using a framework in which utility of an action depended on reward and energetic cost, both discounted in time, we found that it was possible to account for a body of data in which animals were free to choose how to move (reach slow or fast), as well as what to do (walk or fly, produce force F1 or F2). We suggest that some forms of decision-making and motor control may share a common utility in which the brain represents the effort associated with performing an action objectively via its metabolic energy cost and then, like reward, temporally discounts it as a function of movement duration.
Article
When making a subjective choice, the brain must compute a value for each option and compare those values to make a decision. The orbitofrontal cortex (OFC) is critically involved in this process, but the neural mechanisms remain obscure, in part due to limitations in our ability to measure and control the internal deliberations that can alter the dynamics of the decision process. Here we tracked these dynamics by recovering temporally precise neural states from multidimensional data in OFC. During individual choices, OFC alternated between states associated with the value of two available options, with dynamics that predicted whether a subject would decide quickly or vacillate between the two alternatives. Ensembles of value-encoding neurons contributed to these states, with individual neurons shifting activity patterns as the network evaluated each option. Thus, the mechanism of subjective decision-making involves the dynamic activation of OFC states associated with each choice alternative.
Article
When a saccade is expected to result in a reward, both neural activity in oculomotor areas and the saccade itself (e.g. its vigor and latency) are altered (compared to when no reward is expected). As such, it is unclear whether the correlations of neural activity with reward indicate a representation of reward beyond a movement representation; the modulated neural activity may simply represent the differences in motor output due to expected reward. Here, to distinguish between these possibilities, we trained monkeys to perform a natural scene search task while we recorded from the frontal eye field (FEF). Indeed, when reward was expected (i.e., saccades to the target), FEF neurons showed enhanced responses. Moreover, when monkeys accidentally made eye movements to the target, firing rates were lower than when they purposively moved to the target. Thus, neurons were modulated by expected reward rather than simply the presence of the target. We then fit a model that simultaneously included components related to expected reward and saccade parameters. While expected reward led to shorter latency and higher velocity saccades, these behavioral changes could not fully explain the increased FEF firing rates. Thus, FEF neurons appear to encode motivational factors such as reward expectation, above and beyond the kinematic and behavioral consequences of imminent reward.
Article
Vertebrates are remarkable for their ability to select and execute goal-directed actions: motor skills critical for thriving in complex, competitive environments. A key aspect of a motor skill is the ability to execute its component movements over a range of speeds, amplitudes and frequencies (vigor). Recent work has indicated that a subcortical circuit, the basal ganglia, is a critical determinant of movement vigor in rodents and primates. We propose that the basal ganglia evolved from a circuit that in lower vertebrates and some mammals is sufficient to directly command simple or stereotyped movements to one that indirectly controls the vigor of goal-directed movements. The implications of a dual role of the basal ganglia in the control of vigor and response to reward are also discussed.
Article
Action is controlled by both motivation and cognition. The basal ganglia may be the site where these kinds of information meet. Using a memory-guided saccade task with an asymmetric reward schedule, we show that visual and memory responses of caudate neurons are modulated by expectation of reward so profoundly that a neuron's preferred direction often changed with the change in the rewarded direction. The subsequent saccade to the target was earlier and faster for the rewarded direction. Our results indicate that the caudate contributes to the determination of oculomotor outputs by connecting motivational values (for example, expectation of reward) to visual information.
Article
To want something now rather than later is a common attitude that reflects the brain's tendency to value the passage of time. Because the time taken to accomplish an action inevitably delays task achievement and reward acquisition, this idea was ported to neural movement control within the “cost of time” theory. This theory provides a normative framework to account for the underpinnings of movement time formation within the brain and the origin of a self-selected pace in human and animal motion. Then, how does the brain exactly value time in the control of action? To tackle this issue, we used an inverse optimal control approach and developed a general methodology allowing to squarely sample infinitesimal values of the time cost from experimental motion data. The cost of time underlying saccades was found to have a concave growth, thereby confirming previous results on hyperbolic reward discounting, yet without making any prior assumption about this hypothetical nature. For self-paced reaching, however, movement time was primarily valued according to a striking sigmoidal shape; its rate of change consistently presented a steep rise before a maximum was reached and a slower decay was observed. Theoretical properties of uniqueness and robustness of the inferred time cost were established for the class of problems under investigation, thus reinforcing the significance of the present findings. These results may offer a unique opportunity to uncover how the brain values the passage of time in healthy and pathological motor control and shed new light on the processes underlying action invigoration.
Article
An empirical formula was developed from which mean values for energy expenditure per kilogram of body weight (Ew) can be calculated for groups of normal adult males, walking on a motor-driven treadmill with speeds in the range of 35–115 m/min. and gradients in the range of 0–12 degrees. The formula was derived from experiments with two subjects. From the results it appears that Ew increases with the square of speed both in level and grade walking and that log Ew increases linearly with the geometric angle (in degrees). The validity of the formula was tested by experiments with 4 other subjects and experimental data from the literature. A close agreement between actual and predicted values was found. Factors influencing individual values for Ew are discussed. A diagram is presented from which Ew may be read off for various combinations of gradient and speed. Submitted on September 17, 1959
Article
Unlabelled: During value-based decision-making, individuals consider the various options and select the one that provides the maximum subjective value. Although the brain integrates abstract information to compute and compare these values, the only behavioral outcome is often the decision itself. However, if the options are visual stimuli, during deliberation the brain moves the eyes from one stimulus to the other. Previous work suggests that saccade vigor, i.e., peak velocity as a function of amplitude, is greater if reward is associated with the visual stimulus. This raises the possibility that vigor during the free viewing of options may be influenced by the valuation of each option. Here, humans chose between a small, immediate monetary reward and a larger but delayed reward. As the deliberation began, vigor was similar for the saccades made to the two options but diverged 0.5 s before decision time, becoming greater for the preferred option. This difference in vigor increased as a function of the difference in the subjective values that the participant assigned to the delayed and immediate options. After the decision was made, participants continued to gaze at the options, but with reduced vigor, making it possible to infer timing of the decision from the sudden drop in vigor. Therefore, the subjective value that the brain assigned to a stimulus during decision-making affected the motor system via the vigor with which the eyes moved toward that stimulus. Significance statement: We find that, as individuals deliberate between two rewarding options and arrive at a decision, the vigor with which they make saccades to each option reflects a real-time evaluation of that option. With deliberation, saccade vigor diverges between the two options, becoming greater for the option that the individual will eventually choose. The results suggest a shared element between the network that assigns value to a stimulus during the process of decision-making and the net