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ABSTRACT: The elaboration of learning strategies has been considered a key factor to explain sensorimotor learning gains obtained in self-scheduled practice conditions. Nevertheless, the effect of prior knowledge of the testing context (i.e., the learning goal) on that process has been neglected. This study sought to determine whether: (a) learners in a self-controlled condition make different choices contingent on having or not having a learning goal; (b) providing a learning goal would modify the effects of a self-controlled practice condition, and (c) the effect of providing a learning goal would be due to the augmented cognitive effort or to the practice schedule resulting from the learning strategies. The results show that prior knowledge of a variable testing context affects the elaboration of learning strategies and improves skill acquisition in a self-scheduled practice condition. Furthermore, learning gains can be attributed to the self-imposed practice schedule resulting from the learning strategies, and not to the process of elaborating them.
Human movement science 02/2013; · 2.15 Impact Factor
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ABSTRACT: The observation that the activity of multiple muscles can be well approximated by a few linear synergies is viewed by some as a sign that such low-dimensional modules constitute a key component of the neural control system. Here, we argue that the usefulness of muscle synergies as a control principle should be evaluated in terms of errors produced not only in muscle space, but also in task space. We used data from a force-aiming task in two dimensions at the wrist, using an electromyograms (EMG)-driven virtual biomechanics technique that overcomes typical errors in predicting force from recorded EMG, to illustrate through simulation how synergy decomposition inevitably introduces substantial task space errors. Then, we computed the optimal pattern of muscle activation that minimizes summed-squared muscle activities, and demonstrated that synergy decomposition produced similar results on real and simulated data. We further assessed the influence of synergy decomposition on aiming errors (AEs) in a more redundant system, using the optimal muscle pattern computed for the elbow-joint complex (i.e., 13 muscles acting in two dimensions). Because EMG records are typically not available from all contributing muscles, we also explored reconstructions from incomplete sets of muscles. The redundancy of a given set of muscles had opposite effects on the goodness of muscle reconstruction and on task achievement; higher redundancy is associated with better EMG approximation (lower residuals), but with higher AEs. Finally, we showed that the number of synergies required to approximate the optimal muscle pattern for an arbitrary biomechanical system increases with task-space dimensionality, which indicates that the capacity of synergy decomposition to explain behavior depends critically on the scope of the original database. These results have implications regarding the viability of muscle synergy as a putative neural control mechanism, and also as a control algorithm to restore movements.
Frontiers in Computational Neuroscience 01/2013; 7:19. · 2.15 Impact Factor
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ABSTRACT: Previous research using a loud acoustic stimulus (LAS) to investigate motor preparation in reaction time (RT) tasks indicates that responses can be triggered well in advance of the presentation of an imperative stimulus (IS). This is intriguing given that high levels of response preparation cannot be maintained for long periods (≈ 200 ms). In the experiments reported here we sought to assess whether response related activation increases gradually over time in simple RT tasks. In Experiment 1, a LAS was presented at different times just prior to the presentation of the IS to probe the level of activation for the motor response. In Experiment 2, the same LAS was presented at different times after the presentation of the IS. The results provide evidence that response related activation does increase gradually in anticipation of the IS, but it remains stable for a short time after this event. The data display a pattern consistent with the response being triggering by the LAS, rather than a reaction to the IS.
Journal of Neurophysiology 11/2012; · 3.32 Impact Factor
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ABSTRACT: Current methods to reconstruct muscle contributions to joint torque usually combine electromyograms (EMG) with cadaver based estimates of biomechanics, but both are imperfect representations of reality. Here we describe a new method that enables online force reconstruction in which we optimize a "virtual" representation of muscle biomechanics. We first obtain tuning curves for the five major wrist muscles from the mean rectified EMG during the hold-phase of an isometric aiming task, when a cursor is driven by actual force recordings. We then apply a custom, gradient-descent algorithm to determine the set of "virtual pulling vectors" that best reach the target forces when combined with the observed muscle activity. When these pulling vectors are multiplied by the rectified and low-pass filtered (1.3 Hz) EMG of the five muscles online, the reconstructed "force" provides a close spatiotemporal match to the true force exerted at the wrist. In three separate experiments, we demonstrate that the technique works equally well for surface and fine wire recordings, and is sensitive to biomechanical changes elicited by a modification of the forearm posture. In all conditions tested, muscle tuning curves obtained when the task was performed with feedback of reconstructed force were similar to those obtained when the task was performed with real force feedback. This online force reconstruction technique provides new avenues to study the relationship between neural control and limb biomechanics, since the "virtual biomechanics" can be systematically altered at will.
Journal of Neurophysiology 09/2012; · 3.32 Impact Factor
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ABSTRACT: The primate wrist is an ideal model system for studying the reference frames in which movements are coded within the CNS, as a simple rotation of the forearm allows dissociation between extrinsic and body-referenced coordinates. Important information regarding coordinate frame transformations has been obtained using this system, particularly from studies involving extracellular cortical and spinal recordings from monkeys. Because preferred directions of muscle use were reported to rotate by less than half of the joint rotation, the system was considered to dissociate three reference frames: extrinsic (direction of movement in space), muscle (activity of muscles), and joint (angle of the wrist joint). However, given the relatively minor changes in reported muscle biomechanics with human forearm rotation, the reported distinction between joint-space and muscle-space is surprisingly large. Here, we re-assessed patterns of wrist muscle activity with changes in forearm posture in humans, during an isometric force aiming task with a device that enabled stringent control of the musculoskeletal configuration. Results show that the preferred directions for wrist muscle activation closely follow forearm orientation (i.e., by 88%). Control experiments confirmed this whether the hand was clamped passively by a device or grasped a handle. Furthermore, the remaining 12% discrepancy between intended changes in wrist orientation and muscle use also occurred for muscle pulling directions obtained by intramuscular electrical stimulation. The findings prompt reconsideration of data based on the previously reported dissociation between joint-space and muscle-space, and have critical implications for future investigations of sensorimotor transformations and their adaptation using the wrist.
Journal of Neurophysiology 09/2012; · 3.32 Impact Factor
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ABSTRACT: When sharing load among multiple muscles, humans appear to select an optimal pattern of activation that minimizes costs such as the effort or variability of movement. How the nervous system achieves this behavior, however, is unknown. Here we show that contrary to predictions from optimal control theory, habitual muscle activation patterns are surprisingly robust to changes in limb biomechanics. We first developed a method to simulate joint forces in real time from electromyographic recordings of the wrist muscles. When the model was altered to simulate the effects of paralyzing a muscle, the subjects simply increased the recruitment of all muscles to accomplish the task, rather than recruiting only the useful muscles. When the model was altered to make the force output of one muscle unusually noisy, the subjects again persisted in recruiting all muscles rather than eliminating the noisy one. Such habitual coordination patterns were also unaffected by real modifications of biomechanics produced by selectively damaging a muscle without affecting sensory feedback. Subjects naturally use different patterns of muscle contraction to produce the same forces in different pronation-supination postures, but when the simulation was based on a posture different from the actual posture, the recruitment patterns tended to agree with the actual rather than the simulated posture. The results appear inconsistent with computation of motor programs by an optimal controller in the brain. Rather, the brain may learn and recall command programs that result in muscle coordination patterns generated by lower sensorimotor circuitry that are functionally "good-enough."
Journal of Neuroscience 05/2012; 32(21):7384-91. · 7.11 Impact Factor
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ABSTRACT: We investigated the role of visual feedback of task performance in visuomotor adaptation. Participants produced novel two
degrees of freedom movements (elbow flexion–extension, forearm pronation–supination) to move a cursor towards visual targets.
Following trials with no rotation, participants were exposed to a 60° visuomotor rotation, before returning to the non-rotated
condition. A colour cue on each trial permitted identification of the rotated/non-rotated contexts. Participants could not
see their arm but received continuous and concurrent visual feedback (CF) of a cursor representing limb position or post-trial visual feedback (PF) representing the movement trajectory. Separate groups of participants who received CF were
instructed that online modifications of their movements either were, or were not, permissible as a means of improving performance.
Feedforward-mediated performance improvements occurred for both CF and PF groups in the rotated environment. Furthermore,
for CF participants this adaptation occurred regardless of whether feedback modifications of motor commands were permissible.
Upon re-exposure to the non-rotated environment participants in the CF, but not PF, groups exhibited post-training aftereffects, manifested as greater angular deviations from a straight initial trajectory,
with respect to the pre-rotation trials. Accordingly, the nature of the performance improvements that occurred was dependent
upon the timing of the visual feedback of task performance. Continuous visual feedback of task performance during task execution appears critical in realising automatic visuomotor adaptation through a recalibration of the visuomotor mapping
that transforms visual inputs into appropriate motor commands.
KeywordsVisuomotor adaptation-Visual feedback-Sensory information-Motor learning-Contextual (colour) cues
Experimental Brain Research 04/2012; 201(2):191-207. · 2.39 Impact Factor
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ABSTRACT: To intercept or avoid moving objects successfully, we must compensate for the sensorimotor delays associated with visual processing and motor movement. Although straightforward in the case of constant velocity motion, it is unclear how humans compensate for accelerations, as our visual system is relatively poor at detecting changes in velocity. Work on free-falling objects suggests that we are able to predict the effects of gravity, but this represents the most simple, limiting case in which acceleration is constant and motion linear. Here, we show that an internal model also predicts the effects of complex, varying accelerations when they result from lawful interactions with the environment. Participants timed their responses with the arrival of a ball rolling within a tube of various shapes. The pattern of errors indicates that participants were able to compensate for most of the effects of the ball acceleration (∼85%) within a relatively short practice (∼300 trials). Errors on catch trials in which the ball velocity was unexpectedly maintained constant further confirmed that participants were expecting the effect of acceleration induced by the shape of the tube. A similar effect was obtained when the visual scene was projected upside down, indicating that the mechanism of this prediction is flexible and not confined to ecologically valid interactions. These findings demonstrate that the brain is able to predict motion on the basis of prior experience of complex interactions between an object and its environment.
Journal of Neurophysiology 11/2011; 107(3):766-71. · 3.32 Impact Factor
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ABSTRACT: Although rhythmic coordination has been extensively studied in the literature, questions remain about the correspondence of constraints that have been identified in the related contexts of inter-limb and intra-limb coordination. Here we used a 2-DOF robot arm which allows flexible manipulation of forces to investigate the effect on coordination stability of intra-limb coordination of: (i) the synchrony of force requirements and (ii) the involvement of bi-functional muscles. Ten subjects produced simultaneous rhythmic flexion-extension (FE) and supination-pronation (SP) elbow movements in two coordination patterns: (1) flexion synchronized with supination/extension with pronation (in-phase pattern) and (2) flexion synchronized with pronation/extension with supination (anti-phase pattern). The movements were produced with five different settings of the robot arm: a neutral setting that imposed balanced force requirements, and four other settings that increased the force requirements for one direction in both DOF. When combined with specific coordination patterns, these settings created conditions in which either synchronous or alternate patterns of forcing were necessary to perform the task. Results showed that synchronous tasks were more stable than asynchronous tasks (P < 0.05). Within the synchronous tasks, some robot settings were designed to either increase or decrease the use of bi-functional muscles. Although there was no difference for the bi-functional muscle biceps brachii, the coordination was more stable for the condition in which the greatest force requirements corresponded to the mechanical action of the bi-functional pronator teres (P < 0.05). In conclusion, force synchrony increases the stability of rhythmic intra-limb coordination, but further research is needed to clarify the role of bi-functional muscles in this effect.
Experimental Brain Research 08/2011; 213(1):117-24. · 2.39 Impact Factor
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ABSTRACT: Here we investigated the influence of angular separation between visual and motor targets on concurrent adaptation to two opposing visuomotor rotations. We inferred the extent of generalisation between opposing visuomotor rotations at individual target locations based on whether interference (negative transfer) was present. Our main finding was that dual adaptation occurred to opposing visuomotor rotations when each was associated with different visual targets but shared a common motor target. Dual adaptation could have been achieved either within a single sensorimotor map (i.e. with different mappings associated with different ranges of visual input), or by forming two different internal models (the selection of which would be based on contextual information provided by target location). In the present case, the pattern of generalisation was dependent on the relative position of the visual targets associated with each rotation. Visual targets nearest the workspace of the opposing visuomotor rotation exhibited the most interference (i.e. generalisation). When the minimum angular separation between visual targets was increased, the extent of interference was reduced. These results suggest that the separation in the range of sensory inputs is the critical requirement to support dual adaptation within a single sensorimotor mapping.
Experimental Brain Research 07/2011; 212(2):213-24. · 2.39 Impact Factor
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Aymar de Rugy
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ABSTRACT: Reaching to visual targets engages the nervous system in a series of transformations between sensory information and motor commands to muscles. We recently showed that visuomotor adaptation requiring modulation of the activity of the same muscles is more efficient than adaptation requiring a transition to different muscles. Here I specifically tested for adaptation at the level of the final transformation into muscle activation by assessing generalization to unpracticed areas of the workspace, and propose a computational model with modulation of muscle synergies. In the experiment, a visuomotor rotation was applied during a center-out isometric torque production task carefully configured such that adaptation and generalization could be achieved either by only rescaling the contribution of the same muscles, or by additionally requiring the recruitment of different muscles. Consistent with our previous finding, the time course of directional errors revealed that the degree of adaptation was substantially lower (by 28.1%) for the latter case. More importantly, directional error obtained for generalization that required, in principle, to recruit different muscles from these implicated in the adaptation was more than twice that of other generalization areas. Taken together, these results suggest that modulation within an original muscle synergy contributed to visuomotor adaptation, and that synergy recomposition imposed a limitation on both adaptation and generalization. I reproduced these results with a model of the sensorimotor transformation which includes two population codes, one for the sensory network and one for the motor network. Muscle synergies are defined as linear combination of muscles by connections of the motor network, and modulation of these synergies are elicited by adaptation of the weight of these connections. Finally, I speculate that the limitation imposed on synergy recomposition originates in the balance of inhibitory and excitatory mechanisms that operate at different levels of the nervous system, and that contribute to the functional organization of muscle recruitment by focusing activity on relevant muscles.
Human movement science 10/2010; 29(5):684-700. · 2.15 Impact Factor
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ABSTRACT: This manuscript describes how motor behaviour researchers who are not at the same time expert roboticists may implement an experimental apparatus, which has the ability to dictate torque fields around a single joint on one limb or single joints on multiple limbs without otherwise interfering with the inherent dynamics of those joints. Such an apparatus expands the exploratory potential of the researcher wherever experimental distinction of factors may necessitate independent control of torque fields around multiple limbs, or the shaping of torque fields of a given joint independently of its plane of motion, or its directional phase within that plane. The apparatus utilizes torque motors. The challenge with torque motors is that they impose added inertia on limbs and thus attenuate joint dynamics. We eliminated this attenuation by establishing an accurate mathematical model of the robotic device using the Box-Jenkins method, and cancelling out its dynamics by employing the inverse of the model as a compensating controller. A direct measure of the remnant inertial torque as experienced by the hand during a 50 s period of wrist oscillations that increased gradually in frequency from 1.0 to 3.8 Hz confirmed that the removal of the inertial effect of the motor was effectively complete.
Human movement science 10/2010; 29(5):701-12. · 2.15 Impact Factor
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ABSTRACT: When people learn to reach in a novel sensorimotor environment, there are changes in the muscle activity required to achieve task goals. Here, we assessed the time course of changes in muscle directional tuning during acquisition of a new mapping between visual information and isometric force production in the absence of feedback-based error corrections. We also measured the influence of visuomotor adaptation on corticospinal excitability, to test whether any changes in muscle directional tuning are associated with adaptations in the final output components of the sensorimotor control system. Nine right-handed subjects performed a ballistic, center-out isometric target acquisition task with the right wrist (16 targets spaced every 22.5 degrees in the joint space). Surface electromyography was recorded from four major wrist muscles, and motor evoked potentials induced by transcranial magnetic stimulation were measured at baseline, after task execution in the absence of the rotation (A1), after adaptation to the rotation (B), and after a final block of trials without rotation (A2). Changes in the directional tuning of muscles closely matched the rotation of the directional error in force, indicating that the functional contribution of muscles remained consistent over the adaptation period. In contrast to previous motor learning studies, we found only minor changes in the amount of muscular activity and no increase in corticospinal excitability. These results suggest that increased muscle co-activation occurs only when the dynamics of the limb are perturbed and/or that online error corrections or altered force requirements are necessary to elicit a component of the adaptation in the final steps of the transformation between motor goal and muscle activation.
Experimental Brain Research 06/2010; 203(4):701-9. · 2.39 Impact Factor
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ABSTRACT: We investigated the role of visual feedback of task performance in visuomotor adaptation. Participants produced novel two degrees of freedom movements (elbow flexion-extension, forearm pronation-supination) to move a cursor towards visual targets. Following trials with no rotation, participants were exposed to a 60 degrees visuomotor rotation, before returning to the non-rotated condition. A colour cue on each trial permitted identification of the rotated/non-rotated contexts. Participants could not see their arm but received continuous and concurrent visual feedback (CF) of a cursor representing limb position or post-trial visual feedback (PF) representing the movement trajectory. Separate groups of participants who received CF were instructed that online modifications of their movements either were, or were not, permissible as a means of improving performance. Feedforward-mediated performance improvements occurred for both CF and PF groups in the rotated environment. Furthermore, for CF participants this adaptation occurred regardless of whether feedback modifications of motor commands were permissible. Upon re-exposure to the non-rotated environment participants in the CF, but not PF, groups exhibited post-training aftereffects, manifested as greater angular deviations from a straight initial trajectory, with respect to the pre-rotation trials. Accordingly, the nature of the performance improvements that occurred was dependent upon the timing of the visual feedback of task performance. Continuous visual feedback of task performance during task execution appears critical in realising automatic visuomotor adaptation through a recalibration of the visuomotor mapping that transforms visual inputs into appropriate motor commands.
Experimental Brain Research 10/2009; 201(2):191-207. · 2.39 Impact Factor
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ABSTRACT: Reaching to visual targets engages the nervous system in a series of transformations between sensory information and motor commands. That which remains to be determined is the extent to which the processes that mediate sensorimotor adaptation to novel environments engage neural circuits that represent the required movement in joint-based or muscle-based coordinate systems. We sought to establish the contribution of these alternative representations to the process of visuomotor adaptation. To do so we applied a visuomotor rotation during a center-out isometric torque production task that involved flexion/extension and supination/pronation at the elbow-joint complex. In separate sessions, distinct half-quadrant rotations (i.e., 45 degrees ) were applied such that adaptation could be achieved either by only rescaling the individual joint torques (i.e., the visual target and torque target remained in the same quadrant) or by additionally requiring torque reversal at a contributing joint (i.e., the visual target and torque target were in different quadrants). Analysis of the time course of directional errors revealed that the degree of adaptation was lower (by approximately 20%) when reversals in the direction of joint torques were required. It has been established previously that in this task space, a transition between supination and pronation requires the engagement of a different set of muscle synergists, whereas in a transition between flexion and extension no such change is required. The additional observation that the initial level of adaptation was lower and the subsequent aftereffects were smaller, for trials that involved a pronation-supination transition than for those that involved a flexion-extension transition, supports the conclusion that the process of adaptation engaged, at least in part, neural circuits that represent the required motor output in a muscle-based coordinate system.
Journal of Neurophysiology 03/2009; 101(5):2263-9. · 3.32 Impact Factor
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ABSTRACT: How the CNS deals with the issue of motor redundancy remains a central question for motor control research. Here we investigate the means by which neuromuscular and biomechanical factors interact to resolve motor redundancy in rhythmic multijoint arm movements. We used a two-df motorized robot arm to manipulate the dynamics of rhythmic flexion-extension (FE) and supination-pronation (SP) movements at the elbow-joint complex. Participants were required to produce rhythmic FE and SP movements, either in isolation, or in combination (at the phase relationship of their choice), while we recorded the activity of key bi-functional muscles. When performed in combination, most participants spontaneously produced an in-phase pattern of coordination in which flexion is synchronised with supination. The activity of the Biceps Brachii (BB), the strongest arm muscle which also has the largest moment arms in both flexion and supination was significantly higher for FE and SP performed in combination than in isolation, suggesting optimal exploitation of the mechanical advantage of this muscle. In a separate condition, participants were required to produce a rhythmic SP movement while a rhythmic FE movement was imposed by the motorized robot. Simulations based upon a musculoskeletal model of the arm demonstrated that in this context, the most efficient use of the force-velocity relationship of BB requires that an anti-phase pattern of coordination (flexion synchronized with pronation) be produced. In practice, the participants maintained the in-phase behavior, and BB activity was higher than for SP performed in isolation. This finding suggests that the neural organisation underlying the exploitation of bifunctional muscle properties, in the natural context, constrains the system to maintain the "natural" coordination pattern in an altered dynamic environment, even at the cost of reduced biomechanical efficiency. We suggest an important role for afference from the imposed movement in promoting the "natural" pattern. Practical implications for the emerging field of robot-assisted therapy and rehabilitation are briefly mentioned.
Experimental Brain Research 07/2008; 189(4):421-34. · 2.39 Impact Factor
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ABSTRACT: It is well established that the in-phase pattern of bimanual coordination (i.e. a relative phase of 0 degrees ) is more stable than the antiphase pattern (i.e., a relative phase of 180 degrees ), and that a spontaneous transition from antiphase to in-phase typically occurs as the movement frequency is gradually increased. On the basis of results from relative phase perception experiments, Bingham (Proceedings of the 23rd annual conference of the cognitive science society. Laurence Erlbaum Associates, Mahwah, pp 75-79, 2001; Ecol Psychol 16:45-53, 2004; Advances in psychology 135: time-to-contact. Elsevier, Amsterdam, pp 421-442, 2004) proposed a dynamical model that consists of two phase driven oscillators coupled via the perceived relative phase, the resolution of which is determined by relative velocity. In the present study, we specifically test behavioral predictions from this last assumption during a unimanual visuo-motor tracking task. Different conditions of amplitudes and frequencies were designed to manipulate selectively relative phase and relative velocity. While the known effect of phase and frequency were observed, relative phase variability was not affected by the different conditions of relative velocity. As such, Bingham's model assumption that instability in relative phase coordination is brought about by relative velocity that affects the resolution of the perceived relative phase has been invalidated for the case of rhythmic unimanual visuo-motor tracking. Although this does not rule out the view that relative phase production is constrained by relative phase perception, the mechanism that would be responsible for this phenomenon still has to be established.
Experimental Brain Research 02/2008; 184(2):269-73. · 2.39 Impact Factor
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ABSTRACT: The tendency for movements of the upper limbs to be drawn systematically toward one another and to follow similar spatiotemporal trajectories is well known. Although suppression of this tendency is integral to tasks of daily living, its exploitation may prove to be critical in the rehabilitation of acquired hemiplegias. In general, however, the task-related factors that determine the degree of coupling between the upper limbs and the mechanisms that mediate bilateral interactions between neural pathways projecting to the muscles of the arm and hand are not yet well understood. We present evidence that the postural context in which human participants perform upper limb movements determines the relative stability of patterns of bimanual coordination. Manipulation of the axes of rotation of forearm movements reversed the relative stability of simultaneous and alternating patterns of bimanual coordination. Transcranial magnetic stimulation of motor cortex revealed that these manipulations of postural context altered the crossed modulation of excitability in corticospinal pathways that arises from movement of the opposite limb. Furthermore, modulation of responses to electrical stimulation of the cervicomedullary junction indicated that crossed modulation was also expressed at the level of the spinal motoneurons. Our data support the view that crossed modulation of excitability in corticospinal pathways mediates the stability of bimanual coordination. Furthermore, task-related factors that are sufficient to give rise to changes in the stability of bimanual coordination are accompanied by crossed modulation of excitability at multiple levels of the neuraxis, indicative of a failure of inhibitory control.
Journal of Neurophysiology 04/2007; 97(3):2016-23. · 3.32 Impact Factor
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ABSTRACT: In this study we investigate the coordination between rhythmic flexion-extension (FE) and supination-pronation (SP) movements at the elbow joint-complex, while manipulating the intersegmental dynamics by means of a 2-degrees of freedom (df) robot arm. We hypothesized that constraints imposed by the structure of the neuromuscular-skeletal system would (1) result in predominant pattern(s) of coordination in the absence of interaction torques and (2) influence the capabilities of participants to exploit artificially induced interaction torques. Two experiments were conducted in which different conditions of interaction torques were applied on the SP-axis as a function of FE movements. These conditions promoted different patterns of coordination between the 2-df. Control trials conducted in the absence of interaction torques revealed that both the in-phase (supination synchronized with flexion) and the anti-phase (pronation synchronized with flexion) patterns were spontaneously established by participants. The predominance of these patterns of coordination is explained in terms of the mechanical action of bi-articular muscles acting at the elbow joint-complex, and in terms of the reflexes that link the activity of the muscles involved. Results obtained in the different conditions of interaction torques revealed that those neuromuscular-skeletal constraints either impede or favor the exploitation of intersegmental dynamics depending on the context. Interaction torques were indeed found to be exploited to a greater extent in conditions in which the profiles of interaction torques favored one of the two predominant patterns of coordination (i.e., in-phase or anti-phase) as opposed to other patterns of coordination (e.g., 90 degrees or 270 degrees). Those results are discussed in relation to recent studies reporting exploitation of interaction torques in the context of rhythmic movements.
Experimental Brain Research 12/2006; 175(3):439-52. · 2.39 Impact Factor
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ABSTRACT: The present study investigates the coordination between two people oscillating handheld pendulums, with a special emphasis on the influence of the mechanical properties of the effector systems involved. The first part of the study is an experiment in which eight pairs of participants are asked to coordinate the oscillation of their pendulum with the other participant's in an in-phase or antiphase fashion. Two types of pendulums, A and B, having different resonance frequencies (Freq A=0.98 Hz and Freq B=0.64 Hz), were used in different experimental combinations. Results confirm that the preferred frequencies produced by participants while manipulating each pendulum individually were close to the resonance frequencies of the pendulums. In their attempt to synchronize with one another, participants met at common frequencies that were influenced by the mechanical properties of the two pendulums involved. In agreement with previous studies, both the variability of the behavior and the shift in the intended relative phase were found to depend on the task-effector asymmetry, i.e., the difference between the mechanical properties of the effector systems involved. In the second part of the study, we propose a model to account for these results. The model consists of two cross-coupled neuro-mechanical units, each composed of a neural oscillator driving a wrist-pendulum system. Taken individually, each unit reproduced the natural tendency of the participants to freely oscillate a pendulum close to its resonance frequency. When cross-coupled through the vision of the pendulum of the other unit, the two units entrain each other and meet at a common frequency influenced by the mechanical properties of the two pendulums involved. The ability of the proposed model to address the other effects observed as a function of the different conditions of the pendulum and intended mode of coordination is discussed.
Biological Cybernetics 07/2006; 94(6):427-43. · 1.59 Impact Factor
