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Oscillatory Multiplexing of Neural Population Codes for Interval Timing and Working Memory
Abstract
Interval timing and working memory are critical components of cognition that are supported by neural oscillations in prefrontal-striatal-hippocampal circuits. In this review, the properties of interval timing and working memory are explored in terms of behavioral, anatomical, pharmacological, and neurophysiological findings. We then describe the various neurobiological theories that have been developed to explain these cognitive processes – largely independent of each other. Following this, a coupled excitatory-inhibitory oscillation (EIO) model of temporal processing is proposed to address the shared oscillatory properties of interval timing and working memory. Using this integrative approach, we describe a hybrid model explaining how interval timing and working memory can originate from the same oscillatory processes, but differ in terms of which dimension of the neural oscillation is utilized for the extraction of item, temporal order, and duration information. This extension of the striatal beat-frequency (SBF) model of interval timing (Matell and Meck, 2000, 2004) is based on prefrontal-striatal-hippocampal circuit dynamics and has direct relevance to the pathophysiological distortions observed in time perception and working memory in a variety of psychiatric and neurological conditions.
... The neural oscillator models, on the other hand, are grounded in neuronal networks of timing system in the brain, and consistent with the anatomical, behavioral, and pharmacological evidence (Allman & Meck, 2012;Coull et al., 2010;Merchant et al., 2013). The EIO model (Gu et al., 2015), for example, is constructed such that its mechanisms are consistent with phase-amplitude coupling (PAC) between theta and gamma oscillations thought to be involved in both working memory and timing (Axmacher et al., 2010;Canolty & Knight, 2010;Jensen & Colgin, 2007). Integrate-and-fire attractor networks simulating the lateral entorhinal cortex can produce half-phase oscillatory patterns for coding the seconds to minutes range of time (Rolls & Mills, 2019). ...
... The goodness of fit of this approach is yet to be validated. Alternatively, using the ability to store multiple intervals simultaneously, as proposed in the EIO model (Gu et al., 2015), could be another solution to this dynamic acquisition. The second implication of the dynamic acquisition is that the target temporal criterion is acquired quickly, but the reliability of the acquired temporal criterion increases gradually over sessions. ...
... The brain must then resort to additional resources and processes to compute time differences between multiple intervals. In contrast, multiple-oscillator models (Church & Broadbent, 1990;Gu et al., 2015) could, in principle, preserve the magnitudes of the interval timing and the computational accessibility (e.g., in log-spacing oscillators). ...
One of the major challenges for computational models of timing and time perception is to identify a neurobiological plausible implementation that predicts various behavioral properties, including the scalar property and retrospective timing. The available timing models primarily focus on the scalar property and prospective timing, while virtually ignoring the computational accessibility. Here, we first selectively review timing models based on ramping activity, oscillatory pattern, and time cells, and discuss potential challenges for the existing models. We then propose a multifrequency oscillatory model that offers computational accessibility, which could account for a much broader range of timing features, including both retrospective and prospective timing.
... Over the past 50 years or more, numerous behavioral theories of interval timing have been developed, eventually coalescing around the classic Scalar Expectancy Theory (SET − Gibbon, 1977), Scalar Timing Theory (STT, an information-processing model derived from SET − Gibbon et al., 1984), the Behavioral Theory of Timing (BeT − Killeen & Fetterman, 1988), and the Learning-to-Time (LeT − Machado et al., 2009) model. From this solid behavioral foundation, more computational models have emerged, some with neurobiological correlates including oscillation/coincidence-detection models (e.g., Buhusi et al., 2016;Gu et al., 2015;Matell & Meck, 2000, 2004Petter et al., , 2018, drift-diffusion models (e.g., Balcı & Simen, 2014;Luzardo et al., 2013;Emmons et al., 2017;Narayanan, 2016), as well as a variety of state-dependent processes, including population, temporal dynamics, and recurrent neural-network models (e.g., Buonomano, 2014;Goel & Buonomano, 2014;Hardy & Buonomano, 2016;Laje & Buonomano, 2013;Petter & Merchant, 2016;Wang et al., 2018). ...
... Consequently, the proposal is that MSNs act as coincidence detectors for specific cortical oscillatory patterns while multiplexing interval timing and working memory (Buhusi et al., 2016;Gu et al., 2015). These oscillatory patterns can be represented at the level of the MSNs as direct spiking input, a sinusoidal type population signal, or a nearly infinite number of possibilities given the richness of the oscillatory time base (see Matell & Meck, 2004). ...
... There are potentially significant advantages of having an oscillatory time base composed of regularly repeating patterns of oscillation that are widely observed in the cortex and striatum. One is that such regulatory activity is an important aspect of sensory processing and interval timing that allows synchronization of information-processing in different brain areas, including the types of resource allocation underlying dynamic attending and working memory (e.g., Breska & Deouell, 2017;Cravo et al., 2013;Gu et al., 2015;Haegens & Golumbic, 2018;Henry & Herrmann, 2014;Herbst & Landau, 2016;Kösem et al., 2014;Meck & Benson, 2002;Teki et al. (2017) − but see Breska & Deouell, 2016 for an example of when synchronizing to distracting rhythms is detrimental to shifting attention, and van Ede et al., 2018 for a cautionary note on whether neural oscillations contained within certain frequency ranges are best viewed as sustained rhythms or transient burst events). These synchronized oscillations allow the time base to change in a systematic fashion as a function of time, thus proving additional temporal information in the repeated subsets (phase harmonics) of the oscillating time base. ...
The major tenets of beat-frequency/coincidence-detection models of reward-related timing are reviewed in light of recent behavioral and neurobiological findings. This includes the emphasis on a core timing network embedded in the motor system that is comprised of a corticothalamic-basal ganglia circuit. Therein, a central hub provides timing pulses (i.e., predictive signals) to the entire brain, including a set of distributed satellite regions in the cerebellum, cortex, amygdala, and hippocampus that are selectively engaged in timing in a manner that is more dependent upon the specific sensory, behavioral, and contextual requirements of the task. Oscillation/coincidence-detection models also emphasize the importance of a tuned ‘perception’ learning and memory system whereby target durations are detected by striatal networks of medium spiny neurons (MSNs) through the coincidental activation of different neural populations, typically utilizing patterns of oscillatory input from the cortex and thalamus or derivations thereof (e.g., population coding) as a time base. The measure of success of beat-frequency/coincidence-detection accounts, such as the Striatal Beat-Frequency model of reward-related timing (SBF), is their ability to accommodate new experimental findings while maintaining their original framework, thereby making testable experimental predictions concerning diagnosis and treatment of issues related to a variety of dopamine-dependent basal ganglia disorders, including Huntington’s and Parkinson’s disease.
... In fact, as theorized by the attentional allocation model, paying attention only to time induces temporal overestimation, whereas paying attention away from time in favor of other cognitive tasks causes an underestimation of time ( [9,[39][40][41][42]; for reviews, see Refs. [13,37,43]). For example, Brown (1997) found that different types of tasks (such as visual search, pursuit rotor tracking and mental arithmetic tasks) induce duration underestimation, which increases as the difficulty of the task increases. ...
... Particularly, some studies tested the effects of cognitive and attentional tasks on time estimation of ecologically valid time scales (order of 10-100 s) ( [49,61]; for reviews, see Refs. [12,13,37,43]). Time estimation has also been shown to depend on the specific paradigm at hand. Indeed, it has been shown that in a prospective paradigm, in which participants are aware that they must estimate time, cognitive effort decreases the subjective-to-objective duration ratio. ...
... While durations below a second have received a great deal of attention in the human timing literature, a lower number of studies tested the effects of cognitive tasks on such long intervals ( [49,61], for review, see Refs. [12,13,37,43]). However, in ecological situations, human activities require more than just a few seconds, and we usually do have to estimate time in terms of minutes and even more while performing other tasks. ...
The passing of time can be precisely measured by using clocks, whereas humans’ estimation of temporal durations is influenced by many physical, cognitive and contextual factors, which distort our internal clock. Although it has been shown that temporal estimation accuracy is impaired by non-temporal tasks performed at the same time, no studies have investigated how concurrent cognitive and motor tasks interfere with time estimation. Moreover, most experiments only tested time intervals of a few seconds. In the present study, participants were asked to perform cognitive tasks of different difficulties (look, read, solve simple and hard mathematical operations) and estimate durations of up to two minutes, while walking or sitting. The results show that if observers pay attention only to time without performing any other mental task, they tend to overestimate the durations. Meanwhile, the more difficult the concurrent task, the more they tend to underestimate the time. These distortions are even more pronounced when observers are walking. Estimation biases and uncertainties change differently with durations depending on the task, consistent with a fixed relative uncertainty. Our findings show that cognitive and motor systems interact non-linearly and interfere with time perception processes, suggesting that they all compete for the same resources.
... Our motivating examples arises in neurobiology, where individual biological neurons can be viewed as oscillators with periodic spiking and firing of the action potential. Moreover, functional circuits of the brain, such as cortical columns and prefrontal-striatal-hippocampal circuits, are being increasingly interpreted by networks of oscillatory neurons, see [37] for an overview and [17] for modeling specific brain functions such as interval timing and working memory as oscillatory neural networks. Following well-established paths in machine learning such as for convolutional neural networks [29], our focus here is to abstract the essence of functional brain circuits being networks of oscillators and design an RNN based on much simpler mechanistic systems such as those modeled by (2), while ignoring the complicated biological details of neural function. ...
... Inspired by many models in physics, biology and engineering, particularly by circuits of biological neurons [37,17], we proposed a novel RNN architecture (3) based on a model (1) of coupled controlled forced and damped oscillators. For this RNN, we rigorously showed that the hidden states are bounded (5) and obtained precise bounds on the gradients (Jacobians) of the hidden states, (9) and (16). ...
... We will use an induction argument to show the representation formula (17). We start by the outermost product and calculate, ...
Circuits of biological neurons, such as in the functional parts of the brain can be modeled as networks of coupled oscillators. Inspired by the ability of these systems to express a rich set of outputs while keeping (gradients of) state variables bounded, we propose a novel architecture for recurrent neural networks. Our proposed RNN is based on a time-discretization of a system of second-order ordinary differential equations, modeling networks of controlled nonlinear oscillators. We prove precise bounds on the gradients of the hidden states, leading to the mitigation of the exploding and vanishing gradient problem for this RNN. Experiments show that the proposed RNN is comparable in performance to the state of the art on a variety of benchmarks, demonstrating the potential of this architecture to provide stable and accurate RNNs for processing complex sequential data.
... Ramping, or climbing activities in neural oscillations ranging from primarily low frequency gamma band to higher frequency such as beta and alpha band (e.g., Wittmann, 2013) have been revealed as the physiological basis for the model, in addition to neural spikes across a wide range of brain regions such as the striatum (Gu et al., 2015). The time stamps, or accumulated states, are hypothesized to be expressed on both micro (individual neurons) as well as macro (populatory neuron excitation/inhibition) levels (Buonomano & Laje, 2011). ...
... DAT applies exclusively to prospective timing, while in retrospective timing, it is subject to contextual influences and memory retrieval (Block & Gruber, 2014;Gu et al., 2015). ...
... Note that DAT is hypothesized to function mostly within the suprasecond range, because prospective timing recedes with time due to limited capacities of working memory (WM) (for a review, see Gu et al., 2015). Concurrent tasks that require extra attentional resources could reduce timing accuracy (Brown & Boltz, 2002). ...
The current review addresses two internal clock models that have dominated discussions in timing research for the last decades. More specifically, it discusses whether the central or the intrinsic clock model better describes the fluctuations in subjective time. Identifying the timing mechanism is critical to explain and predict timing behaviours in various audiovisual contexts. Music stands out for its prominence in real life scenarios along with its great potential to alter subjective time. An emphasis on how music as a complex dynamic auditory signal affects timing accuracy led us to examine the behavioural and neuropsychological evidence that supports either clock model. In addition to the timing mechanisms, an overview of internal and external variables, such as attention and emotions as well as the classic experimental paradigms is provided, in order to examine how the mechanisms function in response to changes occurring particularly during music experiences. Neither model can explain the effects of music on subjective timing entirely: The intrinsic model applies primarily to subsecond timing, whereas the central model applies to the suprasecond range. In order to explain time experiences in music, one has to consider the target intervals as well as the contextual factors mentioned above. Further research is needed to reconcile the gap between theories, and suggestions for future empirical studies are outlined.
... We briefly note an intriguing similarity between the oscillatory interference models originally designed to model phase precession (O'Keefe and Recce, 1993;Burgess et al., 2007;Burgess, 2008), with the striatum-based excitatory-inhibitory beat frequency model of interval timing (Matell and Meck, 2004;Gu et al., 2015). However, our aim here is not to set out, let alone adjudicate between, different oscillatory-related approaches to timing (e.g., Miall, 1989;Matell and Meck, 2004;Hasselmo, 2011;Itskov et al., 2011;Gu et al., 2015;Wang et al., 2015). ...
... We briefly note an intriguing similarity between the oscillatory interference models originally designed to model phase precession (O'Keefe and Recce, 1993;Burgess et al., 2007;Burgess, 2008), with the striatum-based excitatory-inhibitory beat frequency model of interval timing (Matell and Meck, 2004;Gu et al., 2015). However, our aim here is not to set out, let alone adjudicate between, different oscillatory-related approaches to timing (e.g., Miall, 1989;Matell and Meck, 2004;Hasselmo, 2011;Itskov et al., 2011;Gu et al., 2015;Wang et al., 2015). Rather, our more limited aim is to focus upon arguablyneglected factors controlling variation of oscillatory frequency. ...
Hippocampal theta frequency is a somewhat neglected topic relative to theta power, phase, coherence, and cross-frequency coupling. Accordingly, here we review and present new data on variation in hippocampal theta frequency, focusing on functional associations (temporal coding, anxiety reduction, learning, and memory). Taking the rodent hippocampal theta frequency to running-speed relationship as a model, we identify two doubly-dissociable frequency components: (a) the slope component of the theta frequency-to-stimulus-rate relationship (“theta slope”); and (b) its y-intercept frequency (“theta intercept”). We identify three tonic determinants of hippocampal theta frequency. (1) Hotter temperatures increase theta frequency, potentially consistent with time intervals being judged as shorter when hot. Initial evidence suggests this occurs via the “theta slope” component. (2) Anxiolytic drugs with widely-different post-synaptic and pre-synaptic primary targets share the effect of reducing the “theta intercept” component, supporting notions of a final common pathway in anxiety reduction involving the hippocampus. (3) Novelty reliably decreases, and familiarity increases, theta frequency, acting upon the “theta slope” component. The reliability of this latter finding, and the special status of novelty for learning, prompts us to propose a Novelty Elicits Slowing of Theta frequency (NEST) hypothesis, involving the following elements: (1) Theta frequency slowing in the hippocampal formation is a generalised response to novelty of different types and modalities; (2) Novelty-elicited theta slowing is a hippocampal-formation-wide adaptive response functioning to accommodate the additional need for learning entailed by novelty; (3) Lengthening the theta cycle enhances associativity; (4) Even part-cycle lengthening may boost associativity; and (5) Artificial theta stimulation aimed at enhancing learning should employ low-end theta frequencies.
... Working memory encodes and stores information in its temporal context and permits its further manipulation to guide decision-making and behavior execution [100,101]. The dorsal striatum is involved in the initial storage of temporal information in working memory, and dysfunctions of the striatum or dopaminergic projections to the striatum are known to impair the execution of working memory [102][103][104]. ...
... Memory formation begins when environmental stimuli first elicit a timing mechanism, in which information about elapsed time is stored in working memory or short term. When the stimulus ends or another event happens, the value of that duration is stored in long-term memory [100,136]. The impairments of working memory and the delay in the decision and executive function in cilia-ablated mice further support the speculation of interval timing disruption in these mice. ...
Almost all brain cells contain cilia, antennae-like microtubule-based organelles. Yet, the significance of cilia, once considered vestigial organelles, in the higher-order brain functions is unknown. Cilia act as a hub that senses and transduces environmental sensory stimuli to generate an appropriate cellular response. Similarly, the striatum, a brain structure enriched in cilia, functions as a hub that receives and integrates various types of environmental information to drive appropriate motor response. To understand cilia’s role in the striatum functions, we used loxP/Cre technology to ablate cilia from the dorsal striatum of male mice and monitored the behavioral consequences. Our results revealed an essential role for striatal cilia in the acquisition and brief storage of information, including learning new motor skills, but not in long-term consolidation of information or maintaining habitual/learned motor skills. A fundamental aspect of all disrupted functions was the “time perception/judgment deficit.” Furthermore, the observed behavioral deficits form a cluster pertaining to clinical manifestations overlapping across psychiatric disorders that involve the striatum functions and are known to exhibit timing deficits. Thus, striatal cilia may act as a calibrator of the timing functions of the basal ganglia-cortical circuit by maintaining proper timing perception. Our findings suggest that dysfunctional cilia may contribute to the pathophysiology of neuro-psychiatric disorders, as related to deficits in timing perception.
... Although there is wide consensus that cerebellar structures and prefrontal-striatal-hippocampal networks play a role, different proposals suggest different divisions of labor among these. In particular, the relationship between processing and remembering of absolute durations, relative order, and the relation to a regular isochronous beat has given rise to different hypothetical models [29][30][31][32]. Although the details of these models are under debate, they provide a starting point for understanding the neural implementation of a time-based context signal, as proposed in the most recent formulations of the phonological loop [33]. ...
... What appears to be shared by the tasks is a representation of information unfolding in time that cannot be readily represented as a path in space. Temporal order, possibly based on both absolute duration and relative position, handled by interacting brain networks [30,31], may be an essential component of representations created by the phonological loop. The temporal dimension would be bound to the phonological information related to language networks and motor networks that support articulation. ...
The ability to accurately repeat meaningless nonwords or lists of spoken digits in correct
order have been associated with vocabulary acquisition in both first and second language. Individual differences in these tasks are thought to depend on the phonological loop component of working memory. However, phonological working memory may itself depend on more elementary processes. We asked whether auditory non-verbal short-term memory (STM) for patterns in time supports immediate recall of speech-based sequences. Participants tapped temporal sequences consisting of short and long beeps and repeated nonsense sentences sounding like their native language or an unfamiliar language. As a language learning task, they also memorized familiar-word–foreign-word pairs. Word learning was directly predicted by nonsense sentence repetition accuracy. It was also predicted by temporal pattern STM. However, this association was mediated by performance on the repetition measure. We propose that STM for temporal patterns may reflect a component skill that provides the context signal necessary to encode order in phonological STM. It would be needed to support representation of the prosodic profile of language material, which allows syllables in words and words in sentences to be ordered and temporally grouped for short-term representation and long-term learning.
... Time perception is of particular interest in anxiety because it has been shown to rely on cognitive functions such as attentional control and working memory Droit-Volet & Zélanti, 2013;Gu et al., 2015;Zélanti & Droit-Volet, 2012), which are heavily implicated in anxiety (Moran, 2016;Shi et al., 2019). ...
... As the working memory task is a replication, it also has the benefit of potentially acting as a positive control for the novel time perception task. 2) The effect in the temporal bisection task would be explained by performance differences in working memory between the pathologically anxious and control groups, given the proposed relationship between temporal bisection and working memory Droit-Volet & Zélanti, 2013;Gu et al., 2015;Zélanti & Droit-Volet, 2012). As such, performance in the temporal bisection task should correlate with performance in the working memory task. ...
Anxiety, the state of anticipating that a negative event may occur, can be adaptive by promoting harm-avoidant behaviours, and thus preparing an organism to react to threats. However, it can also spiral out of control, resulting in anxiety disorders, with these being one of the most common mental health issues leading to disability. Despite decades of research, progress on treating anxiety seems to have stalled. This lack of progress has been attributed, at least in part, to the gap between animal and human research. By adopting a cognitive task and anxiety manipulation that are translational, this thesis attempts to bridge the aforementioned gap by investigating the neurocognitive effects of adaptive and pathological anxiety in humans; research that could be in turn translated into animals. Towards that goal, a temporal bisection task and a threat-of-shock manipulation were used. The first experimental chapter (Chapter 3) showed that induced anxiety can reliably shift time perception, while fear does not, suggesting that anxiety and fear might be distinct entities. The second experimental chapter (Chapter 4) attempted to tease apart the mechanism of the aforementioned effect, by investigating whether a load manipulation shifts time perception similarly to induced anxiety. Load did not shift time perception; hence it is unclear whether anxiety leads to temporal alterations via ‘overloading’ limited cognitive resources. The third experimental (Chapter 5) chapter explored the neural correlates of the effect of anxiety on time perception using functional magnetic resonance imaging, employing a pilot and a pre-registered study. The findings suggested some overlap between anxiety and task related processing, leaving open the possibility that anxiety impacts cognition via commandeering finite mental resources. The (preliminary) data of the fourth experimental chapter (Chapter 6) suggested that time perception is not impaired in clinically anxious individuals, but working memory is, highlighting potential dissociations between adaptive and pathological anxiety. In the final chapter the findings are discussed in light of neurocognitive theories of anxiety, alongside a discussion of the overall approach of the thesis and future experiments that could clarify disparate findings.
... As far as the role of theta oscillations, we offer several speculations. A recent review by Gu et al. (2015) proposes a model that integrates interval timing and working memory and that theta oscillations serve as a neural code indexing temporal order, and duration information (Kösem, Gramfort, & van Wassenhove, 2014). In addition, we also speculate that the frontalmidline theta may partially reflect the mental effort dedicated to correcting the encoding erros of temporal information. ...
... Interestingly, such theta correction mechanism was not observed in the suprasecond durations or in participants with self-reported high depression.. This interpretation is consistent with previous reports that encoding of durations involve slow frequency oscillations such as delta-theta oscillations (Gu et al., 2015;Matell & Meck, 2004), and aligns with the perspective that frontal-midline theta oscillations are involved in memory encoding and mental calculation (Gärtner et al., 2015;Hsieh & Ranganath, 2014). Expanding on this, this frontal-midline theta correction mechanism may reflect processes related to conflict and error monitoring (e.g., Curtis & D'Esposito, 2003;Cavanagh and Frank, 2014). ...
Mitigation plans during the early stages of COVID-19 provided a unique, antagonistic environment in which drastic changes occurred quickly and did so with minimal freedom of choice (e.g., involuntary transition from in-person to online classroom). As such, individuals of different beliefs and perspectives would respond differently to these mitigations. We examined the interaction between the Present-Hedonistic (PH) perspective and involuntary classroom transition on the belief in free will (N = 131). PH-oriented individuals exhibit a strong desire for choice while also welcome new opportunities and change. Importantly, the perceived freedom of choice and capacity for change also serve as foundational constructs to the belief in free will. Our results revealed that involuntary transition weakened the free will belief in those with lower PH but did not affect those of higher PH orientation. These findings suggest that the interplay between the perception of choice and capacity for change account for how individuals responded to the COVID-19 pandemic mitigation plans.
... However, the neuronal plausibility of such a coding scheme has been called into doubt: large time intervals would require an accumulator with (near-)unlimited capacity 3 , making it very costly to implement such a mechanism neuronally 4,5 . Given this, alternative timing models have been proposed that use oscillatory patterns or neuronal trajectories to encode temporal information [6][7][8][9] . For example, the striatal beat-frequency model 6,9,10 assumes that time intervals are encoded in the oscillatory firing patterns of cortical neurons, with the length of an interval being discernible, for time judgments, by the similarity of an oscillatory pattern with patterns stored in memory. ...
... Given this, alternative timing models have been proposed that use oscillatory patterns or neuronal trajectories to encode temporal information [6][7][8][9] . For example, the striatal beat-frequency model 6,9,10 assumes that time intervals are encoded in the oscillatory firing patterns of cortical neurons, with the length of an interval being discernible, for time judgments, by the similarity of an oscillatory pattern with patterns stored in memory. Neuronal trajectory models, on the other hand, use intrinsic neuronal patterns as markers for timing. ...
Although time perception is based on the internal representation of time, whether the subjective timeline is scaled linearly or logarithmically remains an open issue. Evidence from previous research is mixed: while the classical internal-clock model assumes a linear scale with scalar variability, there is evidence that logarithmic timing provides a better fit to behavioral data. A major challenge for investigating the nature of the internal scale is that the retrieval process required for time judgments may involve a remapping of the subjective time back to the objective scale, complicating any direct interpretation of behavioral findings. Here, we used a novel approach, requiring rapid intuitive ‘ensemble’ averaging of a whole set of time intervals, to probe the subjective timeline. Specifically, observers’ task was to average a series of successively presented, auditory or visual, intervals in the time range 300–1300 ms. Importantly, the intervals were taken from three sets of durations, which were distributed such that the arithmetic mean (from the linear scale) and the geometric mean (from the logarithmic scale) were clearly distinguishable. Consistently across the three sets and the two presentation modalities, our results revealed subjective averaging to be close to the geometric mean, indicative of a logarithmic timeline underlying time perception.
... Oscillatory multiplexing has been proposed to mediate the integration of information across temporal scales during working memory and interval timing (Gu et al, 2015). Although the precise manner with which oscillatory multiplexing contributes to time estimation remains unclear, a literal read would be that information content, encoded in higher frequency activity, would be integrated over the time scales of the low-frequency oscillations (van Wassenhove, 2016). ...
... Although PAC has been proposed to mediate the integration of information across temporal scales for interval timing (Gu et al., 2015), the precise manner in which counting time would be implemented with oscillatory multiplexing remains difficult to elaborate (van Wassenhove, 2016). To clarify our results, we formulated a direct test of whether the generation of a time interval resulted from the online integration of endogenous information mediated by oscillatory multiplexing and investigated whether α-β PAC predicted timing behavior in an absolute manner between trials. ...
Oscillatory coupling has been implicated in the representation and in the processing of information in the brain. Specific hypotheses suggest that oscillatory coupling may be relevant for the temporal coding of information but to which extent this may translate to conscious timing is unknown. Here, we tested the hypothesis that the temporal precision of self-generated timed actions may be controlled by phase-amplitude coupling (PAC). Using a timing task, we show the existence of significant alpha-beta (α-β) PAC, robust at the individual level, and specific to temporal production. Second, an increase in the strength of α-β PAC was associated with a smaller variance in time production, i.e. an increased precision in timing, but there was no correlation with the duration of the produced interval. Our results suggest an active role for α-β coupling in maintaining the precision of the endogenous temporal goal during time production: specifically, α oscillations may maintain the content of current cognitive states, thus securing the endogenous temporal code for duration estimation instantiated in β band. Oscillatory multiplexing may thus index the variance of neuronal computations, which translates into the precision of behavioral performance.
... However, the neuronal plausibility of such a coding scheme has been called into doubt: large time intervals would require an accumulator with (near-) unlimited capacity 3 , rendering it very costly to implement neuronally 4,5 . Given this, alternative timing models have been proposed that use oscillatory patterns or neuronal trajectories to encode temporal information [6][7][8][9] . For example, the striatal beat-frequency model 6,9,10 assumes that time intervals are encoded in the oscillatory firing patterns of cortical neurons, with the length of an interval being discernible, for time judgements, by the similarity of an oscillatory pattern with patterns stored in memory. ...
... Given this, alternative timing models have been proposed that use oscillatory patterns or neuronal trajectories to encode temporal information [6][7][8][9] . For example, the striatal beat-frequency model 6,9,10 assumes that time intervals are encoded in the oscillatory firing patterns of cortical neurons, with the length of an interval being discernible, for time judgements, by the similarity of an oscillatory pattern with patterns stored in memory. Neuronal trajectory models, on the other hand, use intrinsic neuronal patterns as markers for timing. ...
Although time perception is based on the internal representation of time, whether the subjective timeline is scaled linearly or logarithmically remains an open issue. Evidence from previous research is mixed: while the classical internal-clock model assumes a linear scale with scalar variability, there is evidence that logarithmic timing provides a better fit to behavioral data. A major challenge for investigating the nature of the internal scale is that the retrieval process required for time judgments may involve a remapping of the subjective time back to the objective scale, complicating any direct interpretation of behavioral findings. Here, we used a novel approach, requiring rapid intuitive, 'ensemble' averaging of a whole set of time intervals, to probe the subjective timeline. Specifically, observers' task was to average a series of successively presented, auditory or visual, intervals in the time range 300-1300 ms. Importantly, the intervals were taken from three sets of durations, which were distributed such that the arithmetic mean (from the linear scale) and the geometric mean (from the logarithmic scale) were clearly distinguishable. Consistently across the three sets and the two presentation modalities, our results revealed subjective averaging to be close to the geometric mean, indicative of a logarithmic timeline underlying time perception.
... Conventionally, the scalar property of timing is typically stated as the variability growing proportional to the mean of the target duration(s) being timed (Gibbon et al., 1984(Gibbon et al., , 1997). The SBF model also accounts well for the anatomical, pharmacological, and electrophysiological properties of interval timing (Buhusi and Meck, 2005;Meck, 2006;Balci et al., 2008;Coull et al., 2011;Merchant et al., 2013;Gu et al., 2015Gu et al., , 2018Toda et al., 2017). ...
... The analysis of PC and MSN firing properties as a function of what, whether, when, and how often are becoming more amendable to study given the increase in the availability of online databases where the behavioral, pharmacological, and recording data can be reanalyzed in order to pursue new relations/interpretations while also trying to determine the value of placing older, less precise data in the context of new analysis tools that are rapidly becoming available. This will be especially important in the case of multiplexing the multiple lines of information contained in an individual neuron's signal that is being combined with millions of other neuronal signals and propagated through various networks with the goal of determining time epochs of coincidence and extracting those data points of interest at specific nodes (e.g., Gallistel and King, 2010;Gu et al., 2015;Caruso et al., 2018). ...
The majority of studies in the field of timing and time perception have generally focused on sub- and supra-second time scales, specific behavioral processes, and/or discrete neuronal circuits. In an attempt to find common elements of interval timing from a broader perspective, we review the literature and highlight the need for cell and molecular studies that can delineate the neural mechanisms underlying temporal processing. Moreover, given the recent attention to the function of microtubule proteins and their potential contributions to learning and memory consolidation/re-consolidation, we propose that these proteins play key roles in coding temporal information in cerebellar Purkinje cells (PCs) and striatal medium spiny neurons (MSNs). The presence of microtubules at relevant neuronal sites, as well as their adaptability, dynamic structure, and longevity, makes them a suitable candidate for neural plasticity at both intra- and inter-cellular levels. As a consequence, microtubules appear capable of maintaining a temporal code or engram and thereby regulate the firing patterns of PCs and MSNs known to be involved in interval timing. This proposed mechanism would control the storage of temporal information triggered by postsynaptic activation of mGluR7. This, in turn, leads to alterations in microtubule dynamics through a “read-write” memory process involving alterations in microtubule dynamics and their hexagonal lattice structures involved in the molecular basis of temporal memory.
... These regions have been proposed to interact with the HPC during temporal duration memory (e.g. Gu et al., 2015;MacDonald et al., 2014) and consistent with this, Barnett et al. (2014) observed increased functional connectivity between the HPC and these regions when participants were presented with novel as opposed to old duration information (i.e. duration mismatch trials), suggesting that interaction between the HPC and timing regions supports the encoding of duration information. ...
... In addition to this, the temporal coding of sequences has been suggested to be supported by neural oscillations in the theta band (4-7 Hz) (Buzs� aki and Draguhn, 2004;Hasselmo and Eichenbaum, 2005;Lisman and Idiart, 1995;Lisman and Jensen, 2013;O'Keefe and Recce, 1993;Skaggs et al., 1996) and theta oscillations have been observed in the processing of temporal order (Crivelli-Decker et al., 2018;Heusser et al., 2016;Hsieh et al., 2011). Interestingly, neural oscillations have also been proposed to be involved in memory for duration information (Buhusi and Meck, 2005;Meck, 2004, 2000), and prior work has suggested that the theta rhythm can contribute to the coding of time intervals (Gu et al., 2015;Hasselmo and Stern, 2014). Indeed, hippocampal theta has been demonstrated to be important in the acquisition of trace conditioning (Hoffmann and Berry, 2009), discriminating temporal durations on the order of seconds (Nakazono et al., 2015) and in interacting with classical timing regions during learning such as the cerebellum and striatum (Berke et al., 2004;Hoffmann and Berry, 2009). ...
Although a large body of research has implicated the hippocampus in the processing of memory for temporal duration, there is an exigent degree of inconsistency across studies that obfuscates the precise contributions of this structure. To shed light on this issue, the present review article surveys both historical and recent cross-species evidence emanating from a wide variety of experimental paradigms, identifying areas of convergence and divergence. We suggest that while factors such as time-scale (e.g. the length of durations involved) and the nature of memory processing (e.g. prospective vs. retrospective memory) are very helpful in the interpretation of existing data, an additional important consideration is the context in which the duration information is experienced and processed, with the hippocampus being preferentially involved in memory for durations that are embedded within a sequence of events. We consider the mechanisms that may underpin temporal duration memory and how the same mechanisms may contribute to memory for other aspects of event sequences such as temporal order.
... Prototypical examples include pendulums in mechanics, feedback and relaxation oscillators in electronics, business cycles in economics and heart beat and circadian rhythms in biology. Particularly relevant to our context is the fact that the neurons in our brain can be thought of as oscillators on account of the periodic spiking and firing of the action potential [28,10]. Consequently, functional brain circuits such as cortical columns are being increasingly analyzed in terms of networks of coupled oscillators [28]. ...
Coupled oscillators are being increasingly used as the basis of machine learning (ML) architectures, for instance in sequence modeling, graph representation learning and in physical neural networks that are used in analog ML devices. We introduce an abstract class of neural oscillators that encompasses these architectures and prove that neural oscillators are universal, i.e, they can approximate any continuous and casual operator mapping between time-varying functions, to desired accuracy. This universality result provides theoretical justification for the use of oscillator based ML systems. The proof builds on a fundamental result of independent interest, which shows that a combination of forced harmonic oscillators with a nonlinear read-out suffices to approximate the underlying operators.
... A wide range of research involving dual task paradigms demonstrated a shortening of perceived time with the increasing of the concurrent task difficulty (Brown, 1985;Zakay and Tsal, 1989;Rammsayer and Ulrich, 2005;Castellotti et al., 2022); indeed, as theorized by the attention allocation model, paying attention only to time induces temporal overestimation, whereas diverting attention away from time causes time underestimation, with a positive relationship with the difficulty level of the concurrent nontemporal tasks [ (Burnside, 1971;Thomas and Weaver, 1975;Macar et al., 1994), for reviews, see (Block et al., 2010;Gu et al., 2015)]. ...
Several studies on time estimation showed that the estimation of temporal intervals is related to the amount of attention devoted to time. This is explained by the scalar timing theory, which assumes that attention alters the number of pulses transferred by our internal clock to an accumulator that keeps track of the elapsed time. In a previous study, it was found that time underestimation during cognitive-demanding tasks was more pronounced while walking than while sitting, whereas no clear motor-induced effects emerged without a concurrent cognitive task. What remains unclear then is the motor interference itself on time estimation. Here we aim to clarify how the estimation of time can be influenced by demanding motor mechanisms and how different motor activities interact with concurrent cognitive tasks during time estimation. To this purpose, we manipulated simultaneously the difficulty of the cognitive task (solving arithmetic operations) and the motor task. We used an automated body movement that should require no motor or mental effort, a more difficult movement that requires some motor control, and a highly demanding movement requiring motor coordination and attention. We compared the effects of these three types of walking on time estimation accuracy and uncertainty, arithmetic performance, and reaction times. Our findings confirm that time estimation is affected by the difficulty of the cognitive task whereas we did not find any evidence that time estimation changes with the complexity of our motor task, nor an interaction between walking and the concurrent cognitive tasks. We can conclude that walking, although highly demanding, does not have the same effects as other mental tasks on time estimation.
... Neuroscientists have often characterized strong context-sensitivity in invertebrate models when changes in the inputs to a circuit and/or its neuromodulatory environment (i.e., what neuromodulators are present in the extracellular milieu) shift the circuit's coding properties (Bargmann, 2012;Marder, 2012). Some neuroscientists think these models explain the multi-functionality of cortical regions better than models that presume segregated sub-populations or invariant computations (De Wit & Matheson, 2022;Gu, van Rijn, and Meck, 2015). ...
Functional localization is a central aim of cognitive neuroscience. But the nature and extent of functional localization in the human brain have been subjects of fierce theoretical debate since the 19th Century. In this essay, I first examine how concepts of functional localization have changed over time. I then analyze contemporary challenges to functional localization drawing from research on neural reuse, neural degeneracy, and the context‐dependence of neural functions. I explore the consequences of these challenges for topics in philosophy of science and philosophy of mind including localizationist versus anti‐localizationist approaches to cognitive neuroscience, multiple realizability, reverse inference in functional neuroimaging, and the modularity of mind.
... Multifocal epileptic discharges may be encoded by striatal medium spiny neurons (MSNs) that detect coincident activity, and via the SBF model synchronize the ictal activity to MSNs 'to be timed' signal. [77][78][79] The observation that periodicity changes during SSPE disease progression with shortening of inter-GPD intervals could be explained by higher occurrence of pathological synchronicity and therefore more frequent coincident activity detection in the cerebral cortex due to progressive neuronal loss compared with a normal cortex with higher complexity and variability. ...
Periodic discharges are a rare peculiar electroencephalogram pattern, occasionally associated with motor or other clinical manifestations, usually observed in critically ill patients. Their underlying pathophysiology remains poorly understood. Epileptic spasms in clusters and periodic discharges with motor manifestations share similar electroencephalogram pattern and some aetiologies of unfavourable prognosis such as subacute sclerosing panencephalitis or herpes encephalitis. Arterial spin labelling magnetic resonance imaging identifies localizing ictal and inter-ictal changes in neurovascular coupling, therefore assumed able to reveal concerned cerebral structures. Here, we retrospectively analysed ictal and inter-ictal arterial spin labelling magnetic resonance imaging in patients aged 6 months to 15 years (median 3 years 4 months) with periodic discharges including epileptic spasms, and compared these findings with those of patients with drug-resistant focal epilepsy who never presented periodic discharges nor epileptic spasms as well as to those of age-matched healthy controls. Ictal electroencephalogram was recorded either simultaneously with arterial spin labelling magnetic resonance imaging or during the close time lapse of patients’ periodic discharges, whereas inter-ictal examinations were performed during the patients’ active epilepsy but without seizures during the arterial spin labelling magnetic resonance imaging. Ictal arterial spin labelling magnetic resonance imaging was acquired in five patients with periodic discharges [subacute sclerosing panencephalitis (1), stroke-like events (3), West syndrome with cortical malformation (1), two of them also had inter-ictal arterial spin labelling magnetic resonance imaging]. Inter-ictal group included patients with drug-resistant epileptic spasms of various aetiologies (14) and structural drug-resistant focal epilepsy (8). Cortex, striatum and thalamus were segmented and divided in six functional subregions: prefrontal, motor (rostral, caudal), parietal, occipital and temporal. Rest cerebral blood flow values, absolute and relative to whole brain, were compared with those of age-matched controls for each subregion. Main findings were diffuse striatal as well as cortical motor cerebral blood flow increase during ictal examinations in generalized periodic discharges with motor manifestations (subacute sclerosing panencephalitis) and focal cerebral blood flow increase in corresponding cortical-striatal-thalamic subdivisions in lateralized periodic discharges with or without motor manifestations (stroke-like events and asymmetrical epileptic spasms) with straight topographical correlation with the electroencephalogram focus. For inter-ictal examinations, patients with epileptic spasms disclosed cerebral blood flow changes in corresponding cortical-striatal-thalamic subdivisions (absolute-cerebral blood flow decrease and relative-cerebral blood flow increase), more frequently when compared with the group of drug-resistant focal epilepsies, and not related to Vigabatrin treatment. Our results suggest that corresponding cortical-striatal-thalamic circuits are involved in periodic discharges with and without motor manifestations, including epileptic spasms, opening new insights in their pathophysiology and new therapeutical perspectives. Based on these findings, we propose a model for the generation of periodic discharges and of epileptic spasms combining existing pathophysiological models of cortical-striatal-thalamic network dynamics.
... First, frontal midline theta oscillations are involved in encoding. A recent review by Gu et al. (2015) proposes a model that integrates interval timing and working memory, and that theta oscillations serve as a neural code indexing temporal order and duration information (Kösem et al., 2014). This interpretation is consistent with previous reports that encoding of durations involves slow frequency oscillatory activities such as delta-theta oscillations (Gu et al., 2018;Matell & Meck, 2004), and aligns with the perspective that frontal midline theta oscillations are involved in memory encoding and mental calculation (Gärtner et al., 2015;Hsieh & Ranganath, 2014). ...
A growing collection of observations has demonstrated the presence of multiple neural oscillations participating in human temporal cognition and psychiatric pathologies such as depression and anxiety. However, there remains a gap in the literature regarding the specific roles of these neural oscillations during interval timing, and how these oscillatory activities might vary with the different levels of mental health. The current study examined the participation of the frontal midline theta and occipital alpha oscillations, both of which are prevalent cortical oscillatory markers frequently reported in working memory and time perception paradigms. Participants performed a time reproduction task in the sub- (400, 600, 800 ms) and supra-second timescales (1600, 1800, 2000 ms) while undergoing scalp EEG recordings. Anxiety and depression levels were measured via self-report mental health inventories. Time–frequency analysis of scalp EEG revealed that both frontal midline and occipital alpha oscillations were engaged during the encoding of the durations. Furthermore, we observed that the correlational relationship between frontal midline theta power and the reproduction performance in the sub-second range was modulated by state anxiety. In contrast, the correlational relationship between occipital alpha and the reproduction performance of supra-second intervals was modulated by depression and trait anxiety. The results offer insights on how alpha and theta oscillations differentially play a role in interval timing and how mental health further differentially relates these neural oscillations to sub- and supra-second timescales.
... In tasks that require reproduction of an experienced interval, the performance is linked to the attentional gate and working memory (Block et al. 1998;Mehlabani et al. 2020;Mioni 2018;Mioni et al. 2016). It has been suggested that working memory more actively contribute to the representation of durations in time reproduction tasks through a top-down modulation (Gu et al. 2015). In addition, it is reported that the inter-individual working memory might correlate with time reproduction ability (Broadway and Engle 2011). ...
The timing ability plays an important role in everyday activities and is influenced by several factors such as the attention and arousal levels of the individuals. The effects of these factors on time perception have been interpreted through psychological models of time, including Attentional Gate Model (AGM). On the other hand, research has indicated that neurofeedback (NFB) training improves attention and increases arousal levels in the clinical and healthy population. Regarding the link between attentional processing and arousal levels and NFB and their relation to time perception, this study is a pilot demonstration of the influence of SMR–Beta1 (12–18 Hz) NFB training on time production and reproduction performance in healthy adults. To this end, 12 (9 female and 3 males; M = 26.3, SD = 3.8) and 12 participants (7 female and 5 males; M = 26.9, SD = 3.1) were randomly assigned into the experimental (with SMR–Beta1 NFB) and control groups (without any NFB training), respectively. The experimental group underwent intensive 10 sessions (3 days a week) of the 12–18 Hz up-training. Time production and reproduction performance were assessed pre and post NFB training for all participants. Three-way mixed ANOVA was carried out on T-corrected scores of reproduction and production tasks. Correlation analysis was also performed between SMR–Beta1 and time perception. While NFB training significantly influenced time production (P < 0.01), no such effect was observed for the time reproduction task. The results of the study are finally discussed within the frameworks of AGM, dual-process and cognitive aspects of time perception. Overall, our results contribute to disentangling the underlying mechanisms of temporal performance in healthy individuals.
... The cumulative interference of these spectra throughout the brain results in the overall composition of brain dynamics. The manifestation of previous experiences, current representation, and future trajectories is stochastically embedded within these spatiotemporal spectra [180]. Furthermore, the objective of the brain is to refine its possible instantaneous frequency distributions to optimize its performance in the environment. ...
The human brain is a complex network whose ensemble time evolution is directed by the cumulative interactions of its cellular components, such as neurons and glia cells. Coupled through chemical neurotransmission and receptor activation, these individuals interact with one another to varying degrees by triggering a variety of cellular activity from internal biological reconfigurations to external interactions with other network agents. Consequently, such local dynamic connections mediating the magnitude and direction of influence cells have on one another are highly nonlinear and facilitate, respectively, nonlinear and potentially chaotic multicellular higher-order collaborations. Thus, as a statistical physical system, the nonlinear culmination of local interactions produces complex global emergent network behaviors, enabling the highly dynamical, adaptive, and efficient response of a macroscopic brain network. Microstate reconfigurations are typically facilitated through synaptic and structural plasticity mechanisms that alter the degree of coupling (magnitude of influence) neurons have upon each other, dictating the type of coordinated macrostate emergence in populations of neural cells. These can emerge in the form of local regions of synchronized clusters about a center frequency composed of individual neural cell collaborations as a fundamental form of collective organization. A single mode of synchronization is insufficient for the computational needs of the brain. Thus, as neural components influence one another (cellular components, multiple clusters of synchronous populations, brain nuclei, and even brain regions), different patterns of neural behavior interact with one another to produce an emergent spatiotemporal spectral bandwidth of neural activity corresponding to the dynamical state of the brain network. Furthermore, hierarchical and self-similar structures support these network properties to operate effectively and efficiently. Neuroscience has come a long way since its inception; however, a comprehensive and intuitive understanding of how the brain works is still amiss. It is becoming evident that any singular perspective upon the grandiose biophysical complexity within the brain is inadequate. It is the purpose of this paper to provide an outlook through a multitude of perspectives, including the fundamental biological mechanisms and how these operate within the physical constraints of nature. Upon assessing the state of prior research efforts, in this paper, we identify the path future research effort should pursue to inspire progress in neuroscience.
... Représentation schématique du modèle de la fréquence des battements striataux (Gu, van Rijn & Meck, 2015 ;Matell & Meck, 2000. ...
La majorité des systèmes vivants sont capables d’extraire des informations disponibles dans l’environnement pour estimer des magnitudes. De nombreuses études ont mis en évidence que le traitement de l’espace, du temps et de la numérosité présente des similarités. Deux courants théoriques s’opposent quant à la modélisation du système de traitement des grandeurs. La théorie AToM (Walsh, 2003) défend l’idée d’un système sans hiérarchie ; alors que d’autres, comme la théorie CMT (Casasanto & Boroditsky, 2008) attribuent un rôle prépondérant à l’espace au sein du système. Des processus dédiés au traitement des informations spatiales seraient détournés, adaptés pour rendre possible l’estimation d’autres magnitudes, telles que la numérosité ou le temps (voir Leibovitch et al., 2017). Le principal argument en faveur de cette hiérarchisation est l’asymétrie des effets d’interférence espace-temps. L’espace biaise nos estimations temporelles (effet Kappa), alors que le temps ne semble pas, ou très peu, influencer nos estimations spatiales (effet Tau). L’objectif de cette thèse est d’étudier les conditions d’émergence de l’effet Tau pour affiner les modèles théoriques de l’estimation des magnitudes. Est-il possible d’obtenir une symétrie, voire une asymétrie "inversée", des effets d’interférence espace-temps ? Pourquoi l’effet Tau nécessite une demande élevée en ressources cognitives pour émerger, mais pas l’effet Kappa ? Pour répondre à ces questions, nous avons mis en place un protocole utilisant des tâches d’estimations temporelles et spatiales, durant lesquelles le temps et l’espace variaient de manière orthogonale. La première étude montre qu’en réduisant la discriminabilité des distances, le coût cognitif de la tâche spatiale augmente. Par ricochet, l’effet Tau est amplifié, allant même jusqu’à provoquer une asymétrie inverse des interférences (Tau > Kappa). La seconde étude permet d’écarter l’impact de biais méthodologiques dans les premières expériences. Elle met aussi en lumière un lien entre les performances interindividuelles des participants, et la force de leur effet Tau. De manière plutôt contre-intuitive, cette étude montre que plus un participant est efficace pour estimer l’espace, plus il est interféré par le temps. La troisième étude montre que les effets Tau et Kappa ne sont pas impactés de la même manière par des contextes émotionnels négatifs. L’effet Tau est insensible aux inductions émotionnelles, alors que l’effet Kappa, lui, est amplifié. Nous interprétons l’ensemble de nos résultats en proposant que les effets Tau et Kappa ne prennent pas leurs origines aux mêmes étapes du traitement de l’information. Par conséquent, ils ne seraient pas issus du même processus, et donc du même système. Ces observations nous amènent finalement à questionner l’importance de cette signature comportementale au sein du débat sur la hiérarchisation du système commun du traitement des magnitudes.
... The coordination of neural activity through Mthal, which is anatomically and functionally central to primary motor circuits, is critical to the emergence of effective motor behaviors (Gu, van Rijn, & Meck, 2015). In Chapter 2, I show that two functionally distinct neuronal populations in Mthal are briefly modulated around movement . ...
The motor thalamus (Mthal) is poised between subcortical and cortical motor structures and is, in the simplest terms, understood as a “relay” for neural activity. However, it is increasingly appreciated that Mthal plays a complex, integrative function. This view is emerging from clinical applications where modifying Mthal activity ameliorates the motor symptoms of several movement disorders, including Parkinson’s disease (PD). Little is understood, however, about how neural signals are integrated by Mthal and how this integration shapes ongoing behavior. Answers to these questions hold important implications for basic science and future therapies of brain disease. My studies address major questions about Mthal physiology by recording chronic, in vivo electrophysiology in behaving rats. Given the parallels between rodent and human motor circuits, rats are a useful translational model. I leveraged a two-alternative forced choice task where movement is both ballistic and lateralized. I found that Mthal single unit activity (or “spiking”) is greatly enhanced around movement initiation. Importantly I identified units that fired in a manner that was either “directionally selective” or “non-directionally selective”. Using two performance measures, reaction time (RT) and movement time (MT), I also show that Mthal activity is proportional to the speed of movement. Directionally selective units correlate with RT and MT, non-directionally selective units correlate exclusively with RT. Mthal spiking is known to be correlated with rhythmic oscillations in the extracellular local field potential (LFP). I therefore determined relationships between Mthal unit spiking, behavior and LFP. I discovered that the phase of low frequency oscillations in the delta band (1-4 Hz) predicts spike timing, especially for directionally selective units. Delta phase also predicts RT and aligns to each event, suggesting a role in task timing. The power of higher frequency oscillations, namely beta (13-30 Hz) and low-gamma (30-70 Hz), are nested within the delta phase. Taken together, these results support a model whereby delta phase regulates high-frequency interactions and neuronal excitability in Mthal, which reflects motor performance. To begin parsing behavioral causality with spatiotemporal precision, I implemented a suite of optogenetic tools to anatomically isolate Mthal circuitry. I show that an adeno-associated virus injected in upstream structures can be reliably trafficked to and expressed in Mthal. These techniques establish methods to test hypotheses concerning complex spike-LFP and LFP-LFP interactions ultimately leading to a better understanding of how movement signals are mediated by Mthal.
... With respect to this representation, the wealth of models and theories on timing can be coarsely divided into two classes. In dedicated clock models (e.g., Gibbon, 1977;Gu et al., 2015;Matell & Meck, 2004;van Rijn et al., 2014), the representation of time is functionally decoupled from the imperative stimulus. These models assume that sensory events are processed and subsequently fed into a largely independent timing system. ...
Different theories have been proposed to explain how the human brain derives an accurate sense of time. One specific class of theories, intrinsic clock theories, postulate that temporal information of a stimulus is represented much like other features such as color and location, bound together to form a coherent percept. Here, we explored to what extent this holds for temporal information after it has been perceived and is held in working memory for subsequent comparison. We recorded EEG of participants who were asked to time stimuli at lateral positions of the screen followed by comparison stimuli presented in the center. Using well-established markers of working memory maintenance, we investigated whether the usage of temporal information evoked neural signatures that were indicative of the location where the stimuli had been presented, both during maintenance and during comparison. Behavior and neural measures including the contralateral delay activity, lateralized alpha suppression, and decoding analyses through time all supported the same conclusion: The representation of location was strongly involved during perception of temporal information, but when temporal information was to be used for comparison, it no longer showed a relation to spatial information. These results support a model where the initial perception of a stimulus involves intrinsic computations, but that this information is subsequently translated to a stimulus-independent format to be used to further guide behavior.
... This design enabled to address the possibility of internal timing or duration being explicitly available to awareness through self-referential metacognition (Block, 1995;. Because current neuroscientific models posit that internal dynamics in timing are mediated by oscillatory or statedependent network dynamics (Laje & Buonomano, 2013;Karmarkar & Buonomano, 2007;Buhusi & Meck, 2005;Merchant et al., 2013;Allman et al., 2014;Gu et al., 2015;van Wassenhove, 2016;Bueno et al., 2017), we combined magneto-and electroencephalography (M/EEG) to quantify the dynamics of oscillatory brain responses when participants engaged in self-generated and self-assessed timing. Using a temporal production task to assess metacognition provided several paradigmatic and conceptual benefits. ...
Metacognition, the ability to know about one’s thought process, is self-referential. Here, we combined psychophysics and time-resolved neuroimaging to explore metacognitive inference on the accuracy of a self-generated behavior. Human participants generated a time interval and evaluated the signed magnitude of their temporal production. We show that both self-generation and self-evaluation relied on the power of beta oscillations (β; 15−40 Hz) with increases in early β power predictive of increases in duration. We characterized the dynamics of β power in a low dimensional space (β state-space trajectories) as a function of timing and found that the more distinct trajectories, the more accurate metacognitive inferences were. These results suggest that β states instantiates an internal variable determining the fate of the timing network’s trajectory, possibly as release from inhibition. Altogether, our study describes oscillatory mechanisms for timing, suggesting that temporal metacognition relies on inferential processes of self-generated dynamics.
... Neurobiologically, the Socio-Temporal Brain hypothesis is built on the striatal beat frequency (SBF) model (Gu, van Rijn, & Meck, 2015;Schirmer et al., 2016). ...
Increasing empirical research shows a deep connection between timing processes and neural processing of social information. An integrative theoretical framework for prospective studies in humans was recently proposed, linking timing to sociality. A similar framework guiding research in non-human animals is desirable, ideally encompassing as many taxonomic groups and sensory modalities as possible in order to embrace the diversity of social and timing behaviour across species. Here we expand on a previous theoretical account, introducing this debate to animal behaviour. We suggest adopting an evolutionary perspective on social timing in animals: i.e. a comparative approach to probe the link between temporal and social behaviour across a broad range of animal species. This approach should advance our understanding of animal social timing that is, how social behaviour and timing are mutually affected, and possibly of its evolutionary history in our own lineage. We conclude by identifying outstanding questions and testable hypotheses in animal social timing.
... Neurobiologically, the Socio-Temporal Brain hypothesis is built on the striatal beat frequency (SBF) model (Gu, van Rijn, & Meck, 2015;Schirmer et al., 2016). ...
Increasing empirical research shows a deep connection between timing processes and neural processing of social information. An integrative theoretical framework for prospective studies in humans was recently proposed, linking timing to sociality. A similar framework guiding research in non-human animals is desirable, ideally encompassing as many taxonomic groups and sensory modalities as possible in order to embrace the diversity of social and timing behaviour across species. Here we expand on a previous theoretical account, introducing this debate to animal behaviour. We suggest adopting an evolutionary perspective on social timing in animals: i.e. a comparative approach to probe the link between temporal and social behaviour across a broad range of animal species. This approach should advance our understanding of animal social timing that is, how social behaviour and timing are mutually affected, and possibly of its evolutionary history in our own lineage. We conclude by identifying outstanding questions and testable hypotheses in animal social timing.
... If we assume a generic horizontal section, the diameter of a cortical or hippocampal glutamatergic synapse ranges 0.2-1 μm [15][16][17][18]. Assuming an AZ of circular space and the cleft of $20 nm, we get a volume of cylindrical space which many authors use to study the synaptic transmission by a computer modeling approach [14,16,19]. ...
The brain is probably the most complex machinery for information processing
we can imagine. The amount of data it manages is extremely huge. Any conscious or
unconscious event both internal and coming from the environment needs to be
perceived, elaborated, and responded with an appropriate action. Moreover, the
high-level activities of mind require the connection of logical elaboration, the relationship with past experience (memory), and the transfer of information among
different areas of the brain participating to the elaboration of the thought. Almost
all brain illnesses or even simple defaults can be related to a corruption of the basic
system which manage information in the brain. The main actors in transferring and
managing information are the synapses, and then the understanding of the brain
information processing cannot disregard the full understanding of the synaptic
functionality. In the present chapter, by using as example the most common type of
the brain synapse (the glutamatergic synapse), we will present the basic mechanism
of synaptic transmission stressing some of the most relevant mechanisms which
regulate the transfer and management of information.
... These considerations lead to another question that could be answered in our recently running research project, whether the ''WM-TIP'' relationships are characteristic selectively for millisecond TIP or also for other temporal levels, namely, several hundred millisecond or multisecond domains. There is some evidence that the interval timing (addressed usually multisecond level) and WM can originate from the same oscillatory brain activity and may share common cognitive properties, such as attentional or executive resources (for the recent review see Gu et al., 2015). These common properties were reviewed from behavioral, anatomical, pharmacological, and neuropsychological perspectives. ...
Working memory (WM) is a limited-capacity cognitive system that allows the storage and use of a limited amount of information for a short period of time. Two WM processes can be distinguished: maintenance (i.e., storing, monitoring, and matching information) and manipulation (i.e., reordering and updating information). A number of studies have reported an age-related decline in WM, but the mechanisms underlying this deterioration need to be investigated. Previous research, including studies conducted in our laboratory, revealed that age-related cognitive deficits are related to decreased millisecond timing, i.e., the ability to perceive and organize incoming events in time. The aim of the current study was: (1) to identify in the elderly the brain network involved in the maintenance and manipulation WM processes; and (2) to use an fMRI task to investigate the relation between the brain activity associated with these two processes and the efficiency of temporal information processing (TIP) on a millisecond level reflected by psychophysical indices. Subjects were 41 normal healthy elderly people aged from 62 to 78 years. They performed: (1) an auditory verbal n-back task for assessing WM efficiency in an MRI scanner; and (2) a psychophysical auditory temporal-order judgment (TOJ) task for assessing temporal resolution in the millisecond domain outside the scanner. The n-back task comprised three conditions (0-, 1-, and 2-back), which allowed maintenance (1- vs. 0-back comparisons) and manipulation (2- vs. 1-back comparisons) processes to be distinguished. Results revealed the involvement of a similar brain network in the elderly to that found in previous studies. However, during maintenance processes, we found relatively limited and focused activations, which were significantly extended during manipulation. A novel result of our study, never reported before, is an indication of significant moderate correlations between the efficiency of WM and TIP. These correlations were found only for manipulation but not for maintenance. Our results confirmed the hypothesis that manipulation in the elderly is a dynamic process requiring skilled millisecond timing with high temporal resolution. We conclude that millisecond timing contributes to WM manipulation in the elderly, but not to maintenance.
... In research on non-meditators, brain regions associated with WM processing are prefrontal, parietal and medial temporal regions, with other regions recruited for sensory modality specific WM functions (Christophel et al., 2017;Gu et al., 2015). Oscillatory activity is modulated in these brain regions during performance of WM functions. ...
Objectives
Mindfulness meditation has been shown to improve working memory (WM). However, brain activity underpinning these improvements is underexplored. In meditation-naïve individuals, increased fronto-midline theta and parieto-occipital alpha oscillations, and steeper 1/f aperiodic activity during WM correlate with better WM performance. Resting theta and alpha oscillations have been found to differ in meditators, but WM-related oscillations and 1/f aperiodic activity have not been examined. Additionally, WM-related event-related-potentials (ERPs) are modulated by attention, which is enhanced by mindfulness meditation, so these neural measures are candidate explanations for WM improvement in mindfulness meditators.Methods
We recorded electroencephalography (EEG) from 29 meditation-naïve controls and 29 experienced mindfulness meditators during a Sternberg WM task and compared theta, alpha and 1/f aperiodic activity during the WM delay, and ERPs time-locked to the WM probe.ResultsCompared to controls, meditators demonstrated greater WM accuracy (p = 0.008, Cohen’s d = 0.688), earlier left-temporal ERP responses and a more frontal distribution of activity (FDR-p = 0.0186, η2 = 0.0903), as well as a reduction in overall neural response strength (FDR-p = 0.0098, η2 = 0.1251). A higher proportion of meditators showed theta oscillations during the WM delay, but no other differences in theta, alpha or 1/f aperiodic activity were present.Conclusions
Results suggest that increased WM performance in mindfulness meditators might not result from higher amplitudes of typical WM activity, but instead from an alternative pattern of brain region engagement during WM decision making, allowing more accurate responses with less neural activation (perhaps reflecting increased neural efficiency).
... Oscillatory coupling could mediate the integration of information across temporal scales during interval timing (Gu et al., 2015) so that higher-frequency activity would presumably integrate over the time scales of low-frequency neural activity (van Wassenhove, 2016). The information-theoretic internal clock (Treisman, 1963, for review see Kononowicz and van Wassenhove, 2016) implies that duration estimation results from the integration of information (i.e., a count of number of pulses or events) over time: the high-frequency activity would thus index pulses generated by the pacemaker, whereas low-frequency oscillations would implement the gating and accumulation of pulses. ...
Precise timing is crucial for many behaviors ranging from conversational speech to athletic performance. The precision of motor timing has been suggested to result from the strength of phase–amplitude coupling (PAC) between the phase of alpha oscillations (α, 8–12 Hz) and the power of beta activity (β, 14–30 Hz), herein referred to as α–β PAC. The amplitude of β oscillations has been proposed to code for temporally relevant information and the locking of β power to the phase of α oscillations to maintain timing precision. Motor timing precision has at least two sources of variability: variability of timekeeping mechanism and variability of motor control. It is ambiguous to which of these two factors α–β PAC should be ascribed: α–β PAC could index precision of stopwatch-like internal timekeeping mechanisms, or α–β PAC could index motor control precision. To disentangle these two hypotheses, we tested how oscillatory coupling at different stages of a time reproduction task related to temporal precision. Human participants encoded and subsequently reproduced a time interval while magnetoencephalography was recorded. The data show a robust α–β PAC during both the encoding and reproduction of a temporal interval, a pattern that cannot be predicted by motor control accounts. Specifically, we found that timing precision resulted from the trade-off between the strength of α–β PAC during the encoding and during the reproduction of intervals. These results support the hypothesis that α–β PAC codes for the precision of temporal representations in the human brain.
... How these factors are incorporated within the neural mechanisms underlying human time perception remains poorly understood. Most research on human time perception concentrates on evidencing a pacemaker-driven "internal clock" (2)(3)(4)(5). "Internal clock" approaches posit the existence of an internal timekeeper, specialized for the perception of objective time. Here, regular physiological or neural processes produce rhythmic ticks like the hands of a clock which are counted by an accumulator, such that more ticks corresponds to more time (6). ...
Many contemporary models of time perception are based on the notion that our brain houses an internal "clock", specialized for tracking duration. Here we show that specialized mechanisms are unnecessary, and that human-like duration judgements can be reconstructed from neural responses during sensory processing. Healthy human participants watched naturalistic, silent videos and rated their duration while fMRI was acquired. We constructed a computational model that predicts video durations from salient events in participants' visual cortex activation. This model reproduced biases in participants' subjective reports, whereas control models trained on auditory or somatosensory activity did not. Our data reveal that subjective time is inferred from information arising during the perception of our dynamic sensory environment, providing a computational basis for an end-to-end account of time perception.
... В разработанной недавно формализованной SBF модели кора возбуждает однотипные шипиковые клетки [15, 49,117]. Однако не учтено то обстоя тельство, что активность стрионигральных и стри опаллидарных шипиковых клеток, одновременно возбуждаемых одними и теми же нейронами коры, разнонаправленно модулируется дофамином (см. ...
A mechanism of time perception in subsecond scale, which we proposed earlier [Sil'kis I. UFN. 2011. 42:41–56] now is supplemented in view of that various factors influence the processing of sensory information. This mechanism is based on the assumption that since there is no necessity to determine time parameters of sensory stimuli regardless of their physical properties and there is no special organ for time perception, a processing of all incoming information is performed in the same parallel associative and limbic neural circuits. These circuits are: neocortex (basolateral amygdala) – basal ganglia – thalamus – neocortex (basolateral amygdala), and neocortex – subthalamic nucleus – pedunculopontine nucleus – thalamus – neocortex. The time parameters of a stimulus are determined based on the clock rate of information processing. This rate is inversely proportional to the duration of one cycle of repeated excitation of the neocortex (about 20–25 ms). Such excitation is provided by circulation of activity in mentioned neural circuits. The duration of circulation depends on such factors as the strength of a stimulus, its emotional significance, attention, and current concentrations of neuromodulators. It follows from proposed unified mechanism that any factor reinforcing (weakening) the initial neural representation of physical properties of a stimulus in the neocortex and therefore leading to increase (decrease) in the efficacy of cortico-striatal inputs, should facilitate (hinder) the disinhibition of the thalamus through the basal ganglia and its excitation by the pedunculopontine nucleus. Subsequent decrease (increase) in duration of activity circulation in considered neural loops will cause a rise (fall) in clock rate, and overestimation (underestimation) of perceived time. This mechanism can serve the neurophysiological basis for recently proposed
... This property likely makes it too transient to track time over multiple seconds. Increases in cortical theta have also been associated with interval timing tasks where sustained increases in cortical theta power occur during the encoding of the standard duration in a temporal comparison task [51,52], though whether coherence between HIPP and mPFC remains high across this entire duration has not been tested. ...
... 3. A direct implementation of neural oscillations as pacemakers for time perception has also been deemed computationally intractable (Miall 1989). Alternatively, the internal clock may operate on the logic of coincidence detectors, which would read out the phase synchronization across multiple time scales (Gallistel 1990), or the activity level of oscillators set into activity by a timing task (Gu et al. 2015). This animal model is under active investigation. ...
... This design enabled to address the possibility of internal timing or duration being explicitly available to awareness through self-referential metacognition (Block, 1995;. Because current neuroscientific models posit that internal dynamics in timing are mediated by oscillatory or statedependent network dynamics (Laje & Buonomano, 2013;Karmarkar & Buonomano, 2007;Buhusi & Meck, 2005;Merchant et al., 2013;Allman et al., 2014;Gu et al., 2015;van Wassenhove, 2016;Bueno et al., 2017), we combined magneto-and electroencephalography (M/EEG) to quantify the dynamics of oscillatory brain responses when participants engaged in self-generated and self-assessed timing. Using a temporal production task to assess metacognition provided several paradigmatic and conceptual benefits. ...
Metacognition, the ability to know about one's thought process, is self-referential. Here, we combined psychophysics and time-resolved neuroimaging to explore metacognitive inference on the accuracy of a self-generated behavior. Human participants generated a time interval and evaluated the signed magnitude of their temporal production. We show that both self-generation and self-evaluation relied on the power of beta oscillations (β; 15-40 Hz) with increases in early β power predictive of increases in duration. We characterized the dynamics of β power in a low-dimensional space (β state-space trajectories) as a function of timing and found that the more distinct trajectories, the more accurate metacognitive inferences were. These results suggest that β states instantiate an internal variable determining the fate of the timing network's trajectory, possibly as release from inhibition. Altogether, our study describes oscillatory mechanisms for timing, suggesting that temporal metacognition relies on inferential processes of self-generated dynamics.
... Syllables are fundamental units in determining speech rhythm (Geiser et al., 2008) and speech intelligibility depends strongly on syllabic structure (Ramus et al., 1999) and syllable rhythm (Ghitza & Greenberg, 2009). A large number of studies on interval timing, duration perception, rhythm cognition supports the critical role of the same cortico-basal ganglia-thalamic circuits that we found associated with the 'syllable' condition (e.g., Alm, 2004;Gu, van Rijn, & Meck, 2015;Matell & Meck, 2004;Schirmer, 2004;Teki & Griffiths, 2016;Trost, Fruhholz, Schon, Labbe, Pichon, Grandjean, & Vuilleumier, 2014;Wiener, Turkeltaub, & Coslett, 2010). While the left hemisphere is sensitive to fast events (20-50 ms), the right hemisphere is more sensitive to events at the time scale of syllables (150-250 ms; Boemio, Fromm, Braun, & Poeppel, 2005;Poeppel, 2003). ...
The processing of syllables in visual word recognition was investigated using a novel paradigm based on steady-state visual evoked potentials (SSVEPs). French words were presented to proficient readers in a delayed naming task. Words were split into two segments, the first of which was flickered at 18.75 Hz and the second at 25 Hz. The first segment either matched (congruent condition) or did not match (incongruent condition) the first syllable. The SSVEP responses in the congruent condition showed increased power compared to the responses in the incongruent condition, providing new evidence that syllables are important sublexical units in visual word recognition and reading aloud. With respect to the neural correlates of the effect, syllables elicited an early activation of a right hemisphere network. This network is typically associated with the programming of complex motor sequences, cognitive control and timing. Subsequently, responses were obtained in left hemisphere areas related to phonological processing.
... [17][18][19]. Although theories of time perception vary in the specific cognitive mechanisms or the neural implementations, the standard theory assumes a pacemaker that emits ticks at a regular rate, which are read out by an accumulator (Fig. 1B) 17,[20][21][22][23] . The accumulator can be reset if an event happens that marks the beginning of an interval. ...
Evidence suggests that human timing ability is compromised by heat. In particular, some studies suggest that increasing body temperature speeds up an internal clock, resulting in faster time perception. However, the consequences of this speed-up for other cognitive processes remain unknown. In the current study, we rigorously tested the speed-up hypothesis by inducing passive hyperthermia through immersion of participants in warm water. In addition, we tested how a change in time perception affects performance in decision making under deadline stress. We found that participants underestimate a prelearned temporal interval when body temperature increases, and that their performance in a two-alternative forced-choice task displays signatures of increased time pressure. These results show not only that timing plays an important role in decision-making, but also that this relationship is mediated by temperature. The consequences for decision-making in job environments that are demanding due to changes in body temperature may be considerable.
Across species, neurons track time over the course of seconds to minutes, which may feed the sense of time passing. Herein, we asked whether neural signatures of time-tracking could be found in humans. Participants stayed quietly awake for a few minutes while being recorded with magnetoencephalography. They were unaware they would be asked how long the recording lasted (retrospective time) or instructed beforehand to estimate how long it will last (prospective timing). At rest, rhythmic brain activity is non-stationary and displays bursts of activity in the alpha range (α: 7-14 Hz). When participants were not instructed to attend to time, the relative duration of α bursts linearly predicted individuals’ retrospective estimates of how long their quiet wakefulness lasted. The relative duration of α bursts was a better predictor than α power or burst amplitude. No other rhythmic or arrhythmic activity predicted retrospective duration. However, when participants timed prospectively, the relative duration of α bursts failed to predict their duration estimates. Consistent with this, the amount of α bursts was discriminant between prospective and retrospective timing. Last, with a control experiment, we demonstrate that the relation between α bursts and retrospective time is preserved even when participants are engaged in a visual counting task. Thus, at the time scale of minutes, we report that the relative time of spontaneous α burstiness predicts conscious retrospective time. We conclude that in the absence of overt attention to time, α bursts embody discrete states of awareness constitutive of episodic timing.
Significance Statement
The feeling that time passes is a core component of consciousness and episodic memory. A century ago, brain rhythms called “alpha” were hypothesized to embody an internal clock. However, rhythmic brain activity is non-stationary and displays on-and-off oscillatory bursts, which would serve irregular ticks to the hypothetical clock. Herein, we discovered that in a given lapse of time, the relative bursting time of alpha rhythms is a good indicator of how much time an individual will report to have elapsed. Remarkably, this relation only holds true when the individual does not attend to time and vanishes when attending to it. Our observations suggest that at the scale of minutes, alpha brain activity tracks episodic time.
Impulsive choice is preference for a smaller-sooner (SS) outcome over a larger-later (LL) outcome when LL choices result in greater reinforcement maximization. Delay discounting is a model of impulsive choice that describes the decaying value of a reinforcer over time, with impulsive choice evident when the empirical choice-delay function is steep. Steep discounting is correlated with multiple diseases and disorders. Thus, understanding the processes underlying impulsive choice is a popular topic for investigation. Experimental research has explored the conditions that moderate impulsive choice, and quantitative models of impulsive choice have been developed that elegantly represent the underlying processes. This review spotlights experimental research in impulsive choice covering human and nonhuman animals across the domains of learning, motivation, and cognition. Contemporary models of delay discounting designed to explain the underlying mechanisms of impulsive choice are discussed. These models focus on potential candidate mechanisms, which include perception, delay and/or reinforcer sensitivity, reinforcement maximization, motivation, and cognitive systems. Although the models collectively explain multiple mechanistic phenomena, there are several cognitive processes, such as attention and working memory, that are overlooked. Future research and model development should focus on bridging the gap between quantitative models and empirical phenomena.
Percepcja czasu jest zagadnieniem badanym od ponad 100 lat przez przedstawicieli wielu dyscyplin naukowych. Uważa się, że postrzeganie czasu stanowi kluczową funkcję, która leży u podłoża innych procesów poznawczych. W niniejszej pracy zostały przedstawione modele teoretyczne dotyczące percepcji czasu, począwszy od modeli opartych na badaniach behawioralnych z lat 60. XX wieku, po współczesne modele oparte na badaniach neuroobrazowych. Zaprezentowane zostały niektóre nurty badawcze starające się rozwikłać zagadkę postrzegania czasu, między innymi omówiono relację pomiędzy percepcją czasu a wiekiem i mową. Opisano neurobiologiczne podłoże tego zjawiska oraz przykładowe metody badania percepcji czasu. Artykuł stanowi próbę przybliżenia czytelnikowi tematyki percepcji czasu, która mimo że nieuchwytna i ulotna stanowi fundamentalny wymiar życia ludzkiego.
Durations are defined by a beginning and an end, and a major distinction is drawn between durations that start in the present and end in the future (‘prospective timing’) and durations that start in the past and end either in the past or the present (‘retrospective timing’). Different psychological processes are thought to be engaged in each of these cases. The former is thought to engage a clock-like mechanism that accurately tracks the continuing passage of time, whereas the latter is thought to engage a reconstructive process that utilizes both temporal and non-temporal information from the memory of past events. We propose that, from a biological perspective, these two forms of duration ‘estimation’ are supported by computational processes that are both reliant on population state dynamics but are nevertheless distinct. Prospective timing is effectively carried out in a single step where the ongoing dynamics of population activity directly serve as the computation of duration, whereas retrospective timing is carried out in two steps: the initial generation of population state dynamics through the process of event segmentation and the subsequent computation of duration utilizing the memory of those dynamics. One major form of timing is the estimation of duration. In this Review, Tsao et al. describe the neural bases for estimating ongoing durations and those for estimating durations between past events within memory.
The present research explored the influence of isochronous auditory rhythms on the timing of movement-related prediction in two experiments. In both experiments, participants observed a moving disc that was visible for a predetermined period before disappearing behind a small, medium, or large occluded area for the remainder of its movement. In Experiment 1, the disc was visible for 1 s. During this period, participants were exposed to either a fast or slow auditory rhythm, or they heard nothing. They were instructed to press a key to indicate when they believed the moving disc had reached a specified location on the other side of the occluded area. The procedure measured the (signed) error in participants’ estimate of the time it would take for a moving object to contact a stationary one. The principal results of Experiment 1 were main effects of the rate of the auditory rhythm and of the size of the occlusion on participants’ judgments. In Experiment 2, the period of visibility was varied with size of the occlusion area to keep the total movement time constant for all three levels of occlusion. The results replicated the main effect of rhythm found in Experiment 1 and showed a small, significant interaction, but indicated no main effect of occlusion size. Overall, the results indicate that exposure to fast isochronous auditory rhythms during an interval of inferred motion can influence the imagined rate of such motion and suggest a possible role of an internal rhythmicity in the maintenance of temporally accurate dynamic mental representations.
Different models have been proposed to explain how the human brain derives an accurate sense of time. One specific class of models, intrinsic models, state that temporal information of a stimulus is represented much like other features such as color and location, bound together to form a coherent percept. Here we explored to what extent this holds for temporal information after it has been perceived and is held in working memory for subsequent comparison. We recorded EEG of participants who were asked to time stimuli at lateral positions of the screen followed by comparison stimuli presented in the center. Using well-established markers of working memory maintenance, we investigated whether the usage of temporal information evoked neural signatures that were indicative of the location where the stimuli had been presented, both during maintenance and during comparison. Neural and behavioral measures, including the contralateral delay activity, lateralized alpha suppression and decoding analyses through time, all supported the same conclusion: while the representation of location was strongly involved during the perception of temporal information, once temporal information was committed to memory it no longer showed any relation to spatial information during maintenance or during comparisons. These results support a model where the initial perception of a stimulus involves intrinsic computations, but that this information is subsequently translated to a stimulus-independent format to be used to further guide behavior.
Time Machine is an immersive Virtual Reality installation that explains – in simple terms – the Striatal Beat Frequency (SBF) model of time perception. The installation was created as a collaboration between neuroscientists within the field of time perception along with a team of digital designers and audio composers/engineers. This paper outlines the process, as well as the lessons learned, while designing the virtual reality experience that aims to simplify a complex idea to a novice audience. The authors describe in detail the process of creating the world, the user experience mechanics and the methods of placing information in the virtual place in order to enhance the learning experience. The work was showcased at the 4th International Conference on Time Perspective, where the authors collected feedback from the audience. The paper concludes with a reflection on the work and some suggestions for the next iteration of the project.
Au-delà des symptômes cardinaux qui caractérisent la maladie de Parkinson (MP) – tremblement, akinésie, et rigidité – des déficits rythmiques se manifestent dans différents domaines de coordination motrice, comme au niveau du membre supérieur, de la sphère oro-faciale, ou de la marche. Des altérations rythmiques sont également mises en évidence sur des tâches de perception de rythme (i.e., sur des tâches n’impliquant pas de production motrice). Face à l’étendue des dysfonctionnements rythmiques dans la MP, l’hypothèse d’une dysrythmie généralisée a été formulée. Cette hypothèse implique que l’ensemble des altérations rythmiques qui s’observent au travers de diverses tâches et dans différents systèmes effecteurs partage des mécanismes causaux communs. Néanmoins, cette proposition n’a pas été confirmée à ce jour, et nombre de questions demeurent, tant sur le plan théorique que clinique : les déficits rythmiques caractéristiques de la MP sont-ils réellement liés ? Une source commune aux manifestations rythmiques déficitaires est-elle envisageable ? Si tel est le cas, quels en sont les corrélats cérébraux, et les retombées cliniques ? Élaborée autour de deux principaux axes de recherche, cette dissertation avait pour objectif principal de tester l’hypothèse d’une dysrythmie généralisée dans la MP, au travers de deux questions : i) existe-t-il des liens entre trois domaines de production rythmique (i.e., coordinations oro-faciale, manuelle, et de marche) et un domaine perceptif dans la MP ?; et ii) quel est l’impact d’un entraînement rythmique d’un domaine moteur (i.e., coordination rythmique manuelle) sur d’autres domaines de coordination motrice (i.e., oro-faciales et de la marche) ? L’ensemble des résultats confirme l’hypothèse d’une dysrythmie généralisée dans la MP, et l’existence très probable d’altérations de mécanismes en lien avec une fonction prédictive générale qui, lorsqu’elle est la cible d’un entraînement rythmique, pourrait permettre de réduire certains troubles moteurs dans la MP.
The prefrontal cortex has been implicated in various cognitive processes, including working memory, executive control, decision making, and relational learning. One core computational requirement underlying all these processes is the integration of information across time. When rodents and rabbits associate two temporally discontiguous stimuli, some neurons in the medial prefrontal cortex (mPFC) change firing rates in response to the preceding stimulus and sustain the firing rate during the subsequent temporal interval. These firing patterns are thought to serve as a mechanism to buffer the previously presented stimuli and signal the upcoming stimuli; however, how these critical properties are distributed across different neuron types remains unknown. Here, we investigated the firing selectivity of regular-firing, burst-firing, and fast-spiking neurons in the prelimbic region of the mPFC while rats associated two neutral conditioned stimuli (CS) with one aversive stimulus (US). Analyses of firing patterns of individual neurons and neuron ensembles revealed that regular-firing neurons maintained rich information about CS identity and CS-US contingency during intervals separating the CS and US. Moreover, they further strengthened the latter selectivity with repeated conditioning sessions over a month. The selectivity of burst-firing neurons for both stimulus features was weaker than regular-firing neurons, indicating the difference in task engagement between two subpopulations of putative excitatory neurons. In contrast, putative inhibitory, fast-spiking neurons showed a stronger selectivity for CS identity than CS-US contingency, suggesting their potential role in sensory discrimination. These results revealed a fine-scaled functional organization in the prefrontal network supporting the formation of temporal stimulus associations.
This paper situates an original model of reentrant oscillatory multiplexing within the philosophy of time consciousness to argue for an extensionalist theory of the specious present. I develop a detailed differential latency model of apparent motion to show how the ordinality of experiential content is isomorphic to the ordinality of relevant brain processes. I argue that the theory presented has resources to account for other key features of the specious present, including the representational discreteness between successive conscious moments as well as the phenomenological continuity between them. This work not only shows the plausibility of an extensionalist philosophical theory, it also illustrates the utility of differential latency views in squaring temporal illusions with empirically supported neurodynamics.
Functional dissociations between the medial septal area (MSA) and the nucleus basalis magnocellularis (NBM) were examined using the concepts and experimental procedures developed by scalar timing theory. Rats were tested in variations of a signalled discrete-trial peak-interval schedule of reinforcement in which the response rate functions identified the time when the rats expected reinforcement. The variations assessed aspects of both reference and working memory for information obtained from prior trials and from the current trial. A double dissociation was found in reference memory. Rats with NBM lesions, like those with frontal cortex (FC) lesions, remembered the time of reinforcement as having occurred later than it actually did; rats with MSA lesions, like those with fimbria-fornix (FF) lesions, remembered the time of reinforcement as having occurred earlier than it did. A single dissociation was found in working memory. MSA lesions and FF lesions impaired working memory, while NBM and FC lesions had no effect on it. These data begin to identify the brain mechanisms underlying temporal memory; they indicate that the frontal and hippocampal systems are both involved, but in complementary ways; and they provide information that helps specify more clearly the functions of the frontal and hippocampal systems.
1. An oculomotor delayed-response task was used to examine the spatial memory functions of neurons in primate prefrontal cortex. Monkeys were trained to fixate a central spot during a brief presentation (0.5 s) of a peripheral cue and throughout a subsequent delay period (1-6 s), and then, upon the extinction of the fixation target, to make a saccadic eye movement to where the cue had been presented. Cues were usually presented in one of eight different locations separated by 45 degrees. This task thus requires monkeys to direct their gaze to the location of a remembered visual cue, controls the retinal coordinates of the visual cues, controls the monkey's oculomotor behavior during the delay period, and also allows precise measurement of the timing and direction of the relevant behavioral responses. 2. Recordings were obtained from 288 neurons in the prefrontal cortex within and surrounding the principal sulcus (PS) while monkeys performed this task. An additional 31 neurons in the frontal eye fields (FEF) region within and near the anterior bank of the arcuate sulcus were also studied. 3. Of the 288 PS neurons, 170 exhibited task-related activity during at least one phase of this task and, of these, 87 showed significant excitation or inhibition of activity during the delay period relative to activity during the intertrial interval. 4. Delay period activity was classified as directional for 79% of these 87 neurons in that significant responses only occurred following cues located over a certain range of visual field directions and were weak or absent for other cue directions. The remaining 21% were omnidirectional, i.e., showed comparable delay period activity for all visual field locations tested. Directional preferences, or lack thereof, were maintained across different delay intervals (1-6 s). 5. For 50 of the 87 PS neurons, activity during the delay period was significantly elevated above the neuron's spontaneous rate for at least one cue location; for the remaining 37 neurons only inhibitory delay period activity was seen. Nearly all (92%) neurons with excitatory delay period activity were directional and few (8%) were omnidirectional. Most (62%) neurons with purely inhibitory delay period activity were directional, but a substantial minority (38%) was omnidirectional. 6. Fifteen of the neurons with excitatory directional delay period activity also had significant inhibitory delay period activity for other cue directions. These inhibitory responses were usually strongest for, or centered about, cue directions roughly opposite those optimal for excitatory responses.(ABSTRACT TRUNCATED AT 400 WORDS)
Time is a universal psychological dimension, but time perception has often been studied and discussed in relative isolation. Increasingly, researchers are searching for unifying principles and integrated models that link time perception to other domains. In this review, we survey the links between temporal cognition and other psychological processes. Specifically, we describe how subjective duration is affected by non-temporal stimulus properties (perception), the allocation of processing resources (attention), and past experience with the stimulus (memory). We show that many of these connections instantiate a ‘processing principle’, according to which perceived time is positively related to perceptual vividity and the ease of information-extraction from the stimulus. This empirical generalization generates testable predictions and provides a starting-point for the development of integrated theoretical frameworks. Our intention is that, by outlining some of the links between temporal cognition and other domains, researchers in the field of timing and time perception will be encouraged to situate their work within broader theoretical frameworks, whilst researchers from other fields will be inspired to apply their insights, techniques, and theorizing to improve our understanding of the representation and judgment of time
Many cortical structures have elevated firing rates during working memory, but it is not known how the activity is maintained. To investigate whether reverberating activity is important, we studied the temporal structure of local field potential (LFP) activity and spiking from area LIP in two awake macaques during a memory-saccade task. Using spectral analysis, we found spatially tuned elevated power in the gamma band (25−90 Hz) in LFP and spiking activity during the memory period. Spiking and LFP activity were also coherent in the gamma band but not at lower frequencies. Finally, we decoded LFP activity on a single-trial basis and found that LFP activity in parietal cortex discriminated between preferred and anti-preferred direction with approximately the same accuracy as the spike rate and predicted the time of a planned movement with better accuracy than the spike rate. This finding could accelerate the development of a cortical neural prosthesis.
Cognitive processes such as decision-making, rate calculation and planning require an accurate estimation of durations in the supra-second range—interval timing. In addition to being accurate, interval timing is scale invariant: the time-estimation errors are proportional to the estimated duration.The origin and mechanisms of this fundamental property are unknown. We discuss the computational properties of a circuit consisting of a large number of (input) neural oscillators projecting on a small number of (output) coincidence detector neurons, which allows time to be coded by the pattern of coincidental activation of its inputs. We showed analytically and checked numerically that time-scale invariance emerges from the neural noise. In particular, we found that errors or noise during storing or retrieving information regarding the memorized criterion time produce symmetric, Gaussian-like output whose width increases linearly with the criterion time. In contrast, frequency variability produces an asymmetric, long-tailed Gaussian-like output, that also obeys scale invariant property. In this architecture, time-scale invariance depends neither on the details of the input population, nor on the distribution probability of noise.
The relation between the contingent negative variation (CNV) and time estimation is evaluated in terms of temporal accumulation and preparation processes. The conclusion is that the CNV as measured from the electroencephalogram (EEG) recorded at fronto-central and parietal-central areas is not a direct reflection of the underlying interval timing mechanism(s), but more likely represents a time-based response preparation/ decision-making process.
Recent work shows that putamen-originating beta power oscillations serve as a carrier for temporal information during tapping tasks, with higher beta power associated with longer temporal reproductions. However, given the nature of tapping tasks, it is difficult to determine whether beta power dynamics observed in these tasks are linked to the generation or execution of motor programs or to the internal representation of time. To assess whether recent findings in animals generalize to human studies we reanalyzed existing EEG data of participants who estimated a 2.5 s time interval with self-paced onset and offset keypresses. The results showed that the trial-to-trial beta power measured after the onset predicts the produced duration, such that higher beta power indexes longer produced durations. Moreover, although beta power measured before the first key-press also influenced the estimated interval, it did so independently from post-first-keypress beta power. These results suggest that initial motor inhibition plays an important role in interval production, and that this inhibition can be interpreted as a biased starting point of the decision processes involved in time estimation.
Copyright © 2015. Published by Elsevier Ltd.
Contrary to data showing sensitivity to nontemporal properties of timed signals, current theories of interval timing assume that animals can use the presence or absence of a signal as equally valid cues as long as duration is the most predictive feature. Consequently, the authors examined rats' behavior when timing the absence of a visual or auditory stimulus in trace conditioning and in a "reversed" gap procedure. Memory for timing was tested by presenting the stimulus as a reversed gap into its timed absence. Results suggest that in trace conditioning (Experiment 1), rats time for the absence of a stimulus by using its offset as a time marker. As in the standard gap procedure, the insertion of a reversed gap was expected to "stop" rats' internal clock. In contrast, a reversed gap of 1-, 5-, or 15-s duration "reset" the timing process in both trace conditioning (Experiment 2) and the reversed gap procedure (Experiment 3). A direct comparison of the standard and reversed gap procedures (Experiment 4) supported these findings. Results suggest that attentional mechanisms involving the salience or content of the gap might contribute to the response rule adopted in a gap procedure.
This study investigated the ability of individuals with Parkinson’s disease (PD) to synthesize temporal information across the senses, namely audition and vision. Auditory signals (A) are perceived as lasting longer than visual signals (V) when they are compared together, since attention is captured and sustained more easily than for visual information. We used the audiovisual illusion to probe for disturbances in brain networks that govern the resolution of time in two intersensory conditions that putatively differ in their attention demands. PD patients and controls judged the relative duration of successively presented pairs of unimodal (AA, VV) and crossmodal (VA, AV) signals whilst undergoing fMRI. There were four main findings. First, underestimation of time was exaggerated in PD when timing depended on controlled attention (AV), whereas subtle deficits were found when audition dominated and attention was more easily sustained (VA). Second, group differences in regional activation were observed only for the AV-unimodal comparison, where the PD group failed to modulate basal ganglia, anterior insula, and inferior cerebellum activity in accord with the timing condition. Third, the intersensory timing conditions were dissociated by patterns of abnormal functional connectivity. When intersensory timing emphasized controlled attention, patients showed weakened connectivity of the cortico-thalamus-basal ganglia (CTBG) circuit and the anterior insula with widespread cortical regions, yet enhanced cerebellar connectivity. When audition dominated intersensory timing, patients showed enhanced connectivity of CTBG elements, the anterior insula, and the cerebellum with the caudate tail and frontal cortex. Fourth, abnormal connectivity measures showed excellent sensitivity and specificity in accurately classifying subjects. The results demonstrate that intersensory timing deficits in PD were well characterized by context-dependent patterns of functional connectivity within a presumed core timing system (CTBG) and a ventral attention hub (anterior insula), and enhanced cerebellar connectivity irrespective of the hypothesized attention demands of timing.
Specialization and hierarchy are organizing principles for primate cortex, yet there is little direct evidence for how cortical areas are specialized in the temporal domain. We measured timescales of intrinsic fluctuations in spiking activity across areas and found a hierarchical ordering, with sensory and prefrontal areas exhibiting shorter and longer timescales, respectively. On the basis of our findings, we suggest that intrinsic timescales reflect areal specialization for task-relevant computations over multiple temporal ranges.
Electroencephalographic (EEG) oscillations are hypothesized to reflect cyclical variation in the excitability of neuronal ensembles [1], with particular frequency bands reflecting differing types [2-4] and spatial scales [5-7] of brain operations. Interdependence between the gamma and theta bands [5, 8] suggests an underlying structure to the EEG spectrum, and there is also evidence that ongoing activity influences sensory responses [9, 10]. However, there is no unifying theory of EEG organization and the role of the ongoing oscillatory activity in sensory processing remains controversial. This study analyzed laminar profiles of synaptic activity and action potentials, both spontaneous and stimulus-driven, in primary auditory cortex [11]. We find that -1) The EEG is hierarchically organized; delta (1-4 Hz) phase modulates theta (4-10 Hz) amplitude, and theta phase modulates gamma (30-50 Hz) amplitude. 2) This Oscillatory Hierarchy controls baseline excitability and action potential generation, as well as stimulus-related responses in a neuronal ensemble. We propose that the hierarchical organization of ambient oscillatory activity allows auditory cortex to structure its temporal activity pattern so as to optimize the processing of rhythmic inputs.
Humans and other animals can be shown to process temporal information as if they use an internal stopwatch that can be “run”, “paused”, and “reset” on command and whose speed of “ticking” is adjustable. In addition, interval-timing behavior can be separated into “clock”, “memory”, and “decision” stages of information processing such that one stage can be modified without changing the others. Moreover, interval-timing procedures can be used to diagnose the behavioral abnormalities associated with transgenic, “knock-out”, and “knock-down” mouse models of human diseases. In conjunction with interval-timing tasks, evaluation of spatial memory and emotional regulation provides the necessary information for identifying the most-likely locus of behavioral deficits in genetically modified mice. Consequently, the Timing and Immersive Memory and Emotional Regulation (TIMER) test battery outlined here is recommended as a tool for behavioral phenotyping.
Executive-attention theory proposes a close relationship between working memory capacity (WMC) and cognitive control abilities. However, conflicting results are documented in the literature, with some studies reporting that individual variations in WMC predict differences in cognitive control and trial-to-trial control adjustments (operationalized as the size of the congruency effect and congruency sequence effects, respectively), while others report no WMC-related differences. We hypothesized that brain network dynamics might be a more sensitive measure of WMC-related differences in cognitive control abilities. Thus, in the present study, we measured human EEG during the Simon task to characterize WMC-related differences in the neural dynamics of conflict processing and adaptation to conflict. Although high- and low-WMC individuals did not differ behaviorally, there were substantial WMC-related differences in theta (4–8 Hz) and delta (1–3 Hz) connectivity in fronto-parietal networks. Group differences in local theta and delta power were relatively less pronounced. These results suggest that the relationship between WMC and cognitive control abilities is more strongly reflected in large-scale oscillatory network dynamics than in spatially localized activity or in behavioral task performance.
The last decades have seen a surge in research into interval timing (for recent reviews, see Merchant et al., 2013; Wittmann, 2013; Allman et al., 2014; van Rijn et al., 2014), with some work focussing on the more abstract mechanisms underlying interval timing (e.g., Taatgen et al., 2007) or the role of cognitive faculties such as memory and decision processes on interval timing tasks (e.g., Taatgen and van Rijn, 2011; Shi et al., 2013), but a large proportion of the work focuses the neural substrates of human (e.g., Kononowicz and van Rijn, 2011; Wiener et al., 2012; Kononowicz and Van Rijn, 2014) and animal (e.g., Diaz-Mataix et al., 2013; Bartolo et al., 2014; Cheng et al., 2014) timing processes. Based on this work, we are getting closer to unraveling the biological mechanisms underlying interval timing.
Although the study of time has been central to physics and philosophy for millennia, questions of how time is represented in the brain and how this representation is related to time perception have only recently started to be addressed. Emerging evidence subtly yet profoundly challenges our intuitive notions of time over short scales, offering insight into the nature of the brain's representation of time. Numerous different models, specified at the neural level, of how the brain may keep track of time have been proposed. These models differ in various ways, such as whether time is represented by a centralized or distributed neural system, or whether there are neural systems dedicated to the problem of timing. This paper reviews the insight offered by behavioral experiments and how these experiments refute and guide some of the various models of the brain's representation of time.
The chapters in this book have described current ideas about the functional and neural mechanisms involved in timing behaviors and the temporal judgments of intervals. We optimistically conclude that current and future imaging techniques will soon allow a detailed understanding of the neural circuits involved in interval timing. We can, however, envisage two pitfalls that might slow progress if not treated with caution. The first is the probability that multiple mechanisms are involved in time measurement, and that these are functionally and anatomically discrete. If unrecognized, such duplicity of mechanisms could lead to extreme confusion regarding the locus and function of neural timing systems. The second pitfall is associated with the inherent limitations of neuroimaging techniques and the implications of these for investigations of time measurement. We believe that due to the sluggish and indirect nature of some techniques, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), and the spatial imprecision of others, such as electroencephalography (EEG) and magnetoencephalography (MEG), neuroimaging results must be interpreted with great caution when used to investigate a delicate system such as that used for time measurement.
Although numerous experiments in patients and animals implicate the dopamine (DA) system in timing, there are relatively few studies examining this effect in healthy volunteers. Moreover, the majority of these studies employed tasks of perceptual timing. We therefore investigated the DA modulation of motor timing in healthy volunteers using Acute Phenylalanine/Tyrosine Depletion (APTD), an amino-acid drink that reduces concentrations of the DA precursors tyrosine and phenylalanine. We also examined how APTD's effects on timing might differ as a function of underlying DA function, as indexed by baseline levels of DA precursors. healthy volunteers performed a Mixed Temporal Reproduction task, in which reproduction of five different sample durations (ms– ms) were tested within a single testing block. Reproduction times conformed to Vierordt's Law, such that the shortest durations were overestimated and the longest ones underestimated. Yet contrary to reported effects in Parkinson's disease, we found no DA modulation of this 'migration' effect in our healthy volunteers. Instead, APTD produced systematic shifts in reproduction time across all durations. However, the direction of the shift differed according to individual differences in baseline levels of DA precursor availability. Specifically, APTD slowed reproduction times in participants with low baseline DA precursor levels whereas it speeded them in participants with high baseline levels. These apparently paradoxical effects can be reconciled in terms of the inverted U-shaped relationship between DA function and cognition. Finally, APTD had no effect on a test of temporal production in which participants were asked to provide spontaneous estimates of a one-second time interval. The differential effect of APTD on the reproduction versus production tasks suggests DA modulates the magnitude of the duration initially encoded into working memory, rather than clock-speed.
In a well known article about consciousness Thomas Nagel (1974) raised the fascinating question what it would be like to be a bat. A similar question can be asked with respect to human time consciousness. If our experience of time would turn out to be something that is conceptually unitary, in the sense that it can be defined by a distinct set of related events, attributes, or processes, then it must mean something, however little, to be a Time Experiencer.
Four experiments studied the scaling of time by rats. The purpose was to determine if internal clock and memory processes could be selectively adjusted by pharmacological manipulations. All of the experiments used a temporal discrimination procedure in which one response ("short") was reinforced following a 2-sec noise signal and a different response ("long") was reinforced following an 8-sec noise signal; unreinforced signals of intermediate duration were also presented. The proportion of "long" responses increased as a function of signal duration. All drugs were administered intraperitoneally (ip) and their effect on clock or memory processes was inferred from the observed pattern of change in the point of subjective equality of the psychophysical functions under training and testing conditions. Experiment 1 demonstrated that methamphetamine (1.5 mg/kg) can selectively increase clock speed and that haloperidol (.12 mg/kg) can selectively decrease clock speed. Experiment 2 demonstrated that footshock stress (.2 mA) can selectively increase clock speed during continuous administration but leads to a decrease in clock speed below control values when the footshock is abruptly terminated. Experiment 3 demonstrated that vasopressin (.07 pressor units/kg) and oxytocin (.02 pressor units/kg) can selectively decrease the remembered durations of reinforced times, which suggests that memory storage speed increased. Experiment 4 demonstrated that physostigmine (.01 mg/kg) can selectively decrease the remembered durations of reinforced times and that atropine (.05 mg/kg) can selectively increase these remembered durations, which suggests that memory storage speed was differentially affected. The conclusion is that internal clock and memory processes can be dissociated by selectively adjusting their speed of operation and that these changes can be quantitatively modeled by a scalar timing theory.
An informative and comprehensive review from the leading researchers in the field, this book provides a complete one-stop guide to neuroimaging techniques and their application to a wide range of neuropsychiatric disorders. For each disorder or group of disorders, separate chapters review the most up-to-date findings from structural imaging, functional imaging and/or molecular imaging. Each section ends with an overview from a internationally-renowned luminary in the field, addressing the question of 'What do we know and where are we going?' Richly illustrated throughout, each chapter includes a 'summary box', providing readers with explicit take-home messages. This is an essential resource for clinicians, researchers and trainees who want to learn how neuroimaging tools lead to new discoveries about brain and behaviour associations in neuropsychiatric disorders.
This chapter is divided into two parts. The first describes the effect of Pat Rabbitt's influence in encouraging the first author to use the increasingly sophisticated methods of ageing research to answer questions about the fundamental characteristics of working memory, together with reflections on why so little of this work reached publication. The second part presents a brief review of the literature on working memory and ageing, followed by an account of more recent work attempting to apply the traditional method of experimental dissociation to research on normal ageing and Alzheimer's disease. The discussion suggests that even such simple methods can throw light on both the processes of ageing and the understanding of working memory.
The article focuses on the conversion of Fraser Papers kraft mill in Thurso, Que into Fortress Specialty Cellulose following acquisition. The creation of Fortress Specialty Cellulose, of which Vinall is president and CEO, involved more than just equipment changes at the mill. It involved a change in attitude among employees. Dissolving pulp is really more like a chemical product than a traditional pulp grade, and so a different level of attention to the process is required. The actual start-up took place over the Christmas/New Year's holiday season. Veilleux says the timing forced the people at the mill to jump in and take ownership. Fortress decided to purchase used equipment from a mill in Finland, in order to speed up the mill conversion. The equipment was dismantled and shipped to Montreal. From there, the larger pieces were barged up the Ottawa River. The 15-month conversion project was beset by the usual construction issues, and some unique hurdles. Fortress Specialty Cellulose also has the benefit of an experienced and talented management team.
O'Keefe and Recce [1993] Hippocampus 3:317-330 described an interaction between the hippocampal theta rhythm and the spatial firing of pyramidal cells in the CA1 region of the rat hippocampus: they found that a cell's spike activity advances to earlier phases of the theta cycle as the rat passes through the cell's place field. The present study makes use of large-scale parallel recordings to clarify and extend this finding in several ways: 1) Most CA1 pyramidal cells show maximal activity at the same phase of the theta cycle. Although individual units exhibit deeper modulation, the depth of modulation of CA1 population activity is about 50%. The peak firing of inhibitory interneurons in CA1 occurs about 60 degrees in advance of the peak firing of pyramidal cells, but different interneurons vary widely in their peak phases. 2) The first spikes, as the rat enters a pyramidal cell's place field, come 90 degrees-120 degrees after the phase of maximal pyramidal cell population activity, near the phase where inhibition is least. 3) The phase advance is typically an accelerating, rather than linear, function of position within the place field. 4) These phenomena occur both on linear tracks and in two-dimensional environments where locomotion is not constrained to specific paths. 5) In two-dimensional environments, place-related firing is more spatially specific during the early part of the theta cycle than during the late part. This is also true, to a lesser extent, on a linear track. Thus, spatial selectivity waxes and wanes over the theta cycle. 6) Granule cells of the fascia dentata are also modulated by theta. The depth of modulation for the granule cell population approaches 100%, and the peak activity of the granule cell population comes about 90 degrees earlier in the theta cycle than the peak firing of CA1 pyramidal cells. 7) Granule cells, like pyramidal cells, show robust phase precession. 8) Cross-correlation analysis shows that portions of the temporal sequence of CA1 pyramidal cell place fields are replicated repeatedly within individual theta cycles, in highly compressed form. The compression ratio can be as much as 10:1. These findings indicate that phase precession is a very robust effect, distributed across the entire hippocampal population, and that it is likely to be inherited from the fascia dentata or an earlier stage in the hippocampal circuit, rather than generated intrinsically within CA1. It is hypothesized that the compression of temporal sequences of place fields within individual theta cycles permits the use of long-term potentiation for learning of sequential structure, thereby giving a temporal dimension to hippocampal memory traces.
Lejeune (1998) (Switching or gating? The attentional challenge in cognitive models of psychological time. Behav. Process. 44, 127-45) analyzed and compared two models of prospective timing: the classical switching model and the attentional-gate model. Lejeune argued that a modified switch notion, which can be opened and closed in a frequency which reflects the amount of attentional resources allocated for timing can provide a satisfactory explanation for the impact of attention on prospective timing, and therefore the notion of an 'attentional switch' is favored over adding an 'attentional gate.' In the present analysis, the two competing models are compared in terms of correspondence with the nature of attentional processes, as well as in terms of logical analysis and explanatory power. Based on this comparison, it is argued that gating is a better model of prospective timing than switching.