Biology subjects

Crevecoeur, F.

Publications and source records attributed to Crevecoeur, F..

At least 19 recordsLinked to original sources

bioRxiv2026

Behavioral Markers of Essential Tremor Correlate with Distributed Alteration of Brain Functional Connectivity

Essential Tremor (ET) is a common motor disorder characterized by involuntary oscillations of the upper limbs during voluntary movement. Although increasing evidence implicates dysfunction of the cerebello-thalamo-cortical pathway, ET remains a diagnosis of exclusion, as no definitive biological marker currently exists. To better characterize ET, we recently hypothesized that impaired compensation of sensorimotor delays within the long-latency feedback pathways may generate the tremor-like oscillations observed in ET. This theory suggests that the mean spectral amplitude (MSA), derived from limb kinematics, may serve as a potential marker of ET. Here we investigated the relationship between MSA, standard clinical assessment (Fahn Tolosa Marin Tremor Rating Scale; FTM-TRS), and brain connectivity derived from resting state functional magnetic resonance imaging (rs-fMRI). Using seed-based analyses, we replicated previous findings of reduced functional connectivity between the dentate nucleus and components of the cerebello-thalamo-cortical pathway in ET patients compared with neurologically intact (NI) age-matched participants. Graph-theoretical analyses of whole-brain functional networks revealed distributed alterations in network topology across motor-related cortical and subcortical regions. Several graph metrics correlated with FTM-TRS scores and/or MSA, particularly within motor-related cortical and subcortical circuits, including the thalamus, basal ganglia, and cerebellum in ET. These findings indicate that ET is characterized by distributed alterations in functional brain networks beyond reduced connectivity of dentate nucleus and highlights MSA as a candidate quantitative marker linking altered brain connectivity to sensorimotor delay-driven tremor oscillations.

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bioRxiv2026

Phasic arousal sharpens, rather than amplifies, goal-dependent feedback control

Voluntary movements tolerate variability that does not threaten the goal: when reaching toward a wide target the hand can drift sideways, whereas a narrow target demands tighter control. The nervous system enforces this through corrective feedback responses that scale with task demands, yet how this scaling is set remains unclear. Arousal is a candidate, but how it would act is contested: the classical view casts it as a global amplifier that raises neural gain uniformly, whereas a more recent account holds that it is selective, strengthening task-relevant signals while suppressing others. These accounts make opposite predictions for goal-dependent feedback control, which we tested causally. In 27 human participants (24 {+/-} 2.7 years old) reaching toward narrow or wide targets on a KINARM robot, a 4-second pulsed train of transcutaneous auricular vagus nerve stimulation (taVNS) evoked a phasic boost of arousal before each movement, confirmed by pupil dilation. On a subset of trials the robot applied a mechanical perturbation during the reach, and we measured the corrective muscle activity it evoked in the short- and long-latency reflex windows. The results favored the selective account. Phasic arousal sharpened corrections to the goal: it amplified the difference between narrow and wide responses in the long-latency window, the established readout of goal-dependent control, and suppressed the short-latency response, normally insensitive to the goal, specifically for the wide target, where deviations are harmless. Phasic arousal therefore does not energize the motor system indiscriminately but allocates corrective control to where it serves the task, extending the principle of selective gain, established in perception and memory, to the online control of movement.

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bioRxiv2026

When anticipation is not enough: a mixture of robust and adaptive feedback control strategies improve reaching in dynamic environments

Successful goal-directed movements depend on the central nervous systems (CNS) ability to handle diverse physical interactions. The CNS is thought to handle different dynamical contexts through three mechanisms: (i) trial-by-trial adaptation when forces are predictable, (ii) a model-free robust control strategy, and (iii) online adaptation of feedback responses. While each has been studied independently, their relative contributions and the possibility that they are recruited to different extents across contexts is unknown. Here, we quantified all three strategies within the same individuals to examine how CNS exploits them under varying environmental conditions. Participants (19 female, 15 male) performed reaching tasks while interacting with robot-generated force-fields that were either consistent or varied unpredictably. Trial-by-trial adaptation was measured using standard force channels to isolate anticipatory compensation. Robust control was assessed through movement velocity and corrective force magnitude. Online adaptive control was quantified by the temporal alignment between commanded and measured forces within a movement. Results showed that participants improved anticipatory compensation in consistent environments and relied on both robust and online adaptation when perturbations were unpredictable. Crucially, markers of robust control dominated the early movement phase, whereas online adaptation dominated later corrections. This temporal dissociation was confirmed by electromyographic recordings. Markers of robust and online adaptive feedback strategies also statistically predicted participants ability to adapt across trials in consistent environments, revealing a common trait linking online control and adaptation. These findings reveal a rich and flexible combination of control mechanisms, offering a new framework for understanding the neurophysiological bases of reaching control. Significance StatementHuman reaching control is a complex behavior resulting from several mechanisms that orchestrate feedback responses to mechanical perturbations and adaptation to changes in the environment. Here we combine previously studied paradigms to highlight within the same groups of healthy volunteers that three major components are recruited to different extents dependent on the context: unpredictable environment promote concomitant use of robust control and online adaptation whereas predictable environments recruit standard adaptation based on anticipatory compensation. Remarkably, individuals adaptive capabilities correlated across consistent and inconsistent environments, suggesting a key involvement of adaptive mechanisms in both online control and trial-by-trial adaptation. Robust control, online adaptation, and anticipatory compensation are dissociable behaviorally, and are used to varying levels as a result of individual traits.

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bioRxiv2025

Infinite horizon control captures modulation of movement duration in reaching movements

Movement duration, a fundamental aspect of motor control, is often viewed as a pre-programmed parameter requiring dedicated selection mechanisms. An alternative view posits that movement duration emerges from the control policy itself. Here, we demonstrate, using infinite horizon optimal feedback control (IHOFC) and nonlinear limb dynamics that this alternative hypothesis successfully captures diverse aspects of human reaching behavior, including tradeoffs between movement duration and task parameters. Specifically, we reproduced the modulation of movement duration with varying reach distances and accuracy (Fitts law), and extended the infinite horizon framework to include the effect of rewards and biomechanical costs. Furthermore, our model also featured a temporal evolution of feedback responses to perturbations that resembles experimental observations, and naturally accounted for motor decisions observed when participants select one among multiple goals in dynamic environments. Together, these developments show that in many cases, movement duration may not need to be specified a priori, but instead could result from task-dependent control policies. This framework validates a candidate explanation for varied movement durations, which invites to reconsider the nature and strength of evidence for the finite horizon formulation.

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bioRxiv2025

Measured and modelled transitions between self-paced walking and synchronization with rhythmic auditory cues

Constraining gait rhythm with a metronome has been shown to influence gait pattern in many different ways. While rhythmic cues can improve several parameters in some clinical populations, they do alter the long-range autocorrelations naturally exhibited in series of stride durations. However, transitions between walking with and without a metronome (and vice versa) have not been measured; it is therefore unclear how people adapt to such a change in task. To address this gap, a total of 21 healthy volunteers were asked to walk overground under three conditions: one unconstrained control condition, followed by two conditions in which a metronome was activated during either the first or second half of the trial to test both transitions. The long-range autocorrelations were assessed over a sliding window on the stride series to measure their evolution. Our observations were reproduced with a computational model allowing us to relate sudden changes in movement parameters to the long-range autocorrelations, which are typically measured over longer timescales. The results showed a clear transition in both conditions involving a metronome, with long-range autocorrelations of the series of stride durations gradually reduced when the metronome was turned on and recovered when it was turned off. In these two conditions, the change in long-range autocorrelations could be reproduced in the model by an instantaneous switching of the control policy associated with the presence or not of the metronome, suggesting that long-range autocorrelations emerge from a flexible control strategy that rapidly regulates timing and amplitude parameters according to task requirements. Significant statementThrough an experiment involving transitions between walking with and without a metronome, we studied how people adapt to such a change of task by measuring the evolution of long-range autocorrelations (LRA) in the stride series. The results were reproduced in a model by an instantaneous change in the control policy, which validates the hypothesis that LRA emerge from a flexible control that rapidly regulates timing and amplitude parameters according to task requirements.

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bioRxiv2025

Interference between flexible and adaptive reaching control

Humans rapidly update the control of an ongoing movement following changes in contextual parameters. This involves adjusting the controller to exploit redundancy in the movement goal, such as when reaching for a narrow or wide target, and adapting to dynamic changes such as velocity-dependent force fields (FFs). Although flexible control and motor adaptation are computationally distinct, the fact that both unfold within the same movement suggests they may share common neural resources for task-specific adjustments. To test this hypothesis, we conducted a series of experiments combining changes in the target structure and a force field presented separately or in combination. Seventy-six human participants (both sexes) took part in this study, with each experiment involving different participants. They were asked to reach for a target that could change from a narrow square to a wide rectangle between or during trials. Step loads were used to assess whether participants exploited target redundancy. In a separate experiment, we added a force field in addition to target changes and step loads. Our results revealed a reduced ability to exploit target redundancy when sudden target changes occurred concurrently with FF adaptation. Furthermore, the magnitude of adaptation was reduced when step loads were added to the FF. Crucially, this interference emerged specifically when all perturbations impacted motor execution simultaneously. These results indicate that flexible control and motor adaptation interact in a non-trivial manner, suggesting possible overlap between their underlying neural mechanisms, and a clear identification of the timescale at which they are engaged - namely, during movement. Significant statementHumans rapidly adapt to changes in task demands, such as target structure changes or exposure to force fields (FFs). These two types of adjustments occur within a single movement, suggesting potential interactions between them. Our experiments revealed that the combination of FF exposure with online target shape changes selectively reduced participants ability to exploit target redundancy, while the combination of FF and step loads led to a reduced extent of motor adaptation. These findings confirm that motor adaptation occurs not only between trials but also during movement. The selective nature of the observed interference highlights an interplay between flexible control and motor adaptation, underscoring the importance of understanding the timing of these processes to better characterise their underlying neural circuits.

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bioRxiv2025

Neural Population Mechanisms for Flexible Sensorimotor Control

Modern large-scale recordings have revealed that motor cortex activity during reaching follows low-dimensional dynamics, thought to reflect sensorimotor computations underlying muscle activation. However, the origin of these low dimensional patterns, and how they flexibly reorganize across different tasks remain unclear. Here we demonstrate that the key features of neural activity can naturally emerge in a linear model combining a random network with a biomechanical system. Remarkably, this model shows explicitly how a fixed network can achieve flexible control of multiple behaviours through optimal mapping of sensory feedback onto the network. Finally, analytical decomposition of the controller reveals that low-dimensional network dynamics follow directly from the propagation of low-dimensional feedback signals from the biomechanical plant through the network. This formalism provides a computational framework to interpret flexible motor control in the nervous system, which directly links neural population dynamics to sensorimotor behavior.

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bioRxiv2024

Parallel feedback processing for voluntary control: knowledge of spinal feedback in motor cortex

How hierarchical feedback pathways coordinate goal-directed motor corrections remains unknown. We show that systematic increases in spinal reflex responses to applied loads lead to a reciprocal reduction in the neural response in primary motor cortex. We use a neural network model to highlight how knowledge on lower-level feedback processing (i.e. spinal reflexes) can be embedded into a network to generate goal-directed corrections through parallel feedback pathways.

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bioRxiv2024

Erroneous compensation for long-latency feedback delays as origin of Essential Tremor

Essential tremor (ET), a movement disorder characterized by involuntary oscillations of the limbs during movement, remains to date not well understood. It has been recently suggested that the tremor originates from impaired delay compensation, affecting movement representation and online control. Here we tested this hypothesis directly with ET patients (N=24) and neurologically intact (NI) volunteers (N=28) in an upper limb postural perturbation task. After maintaining their hand in a visual target, participants experienced perturbations of unpredictable direction and magnitude, and were instructed to counter the perturbation and steer their hand back to the starting position. In comparison with NI volunteers, ET patients early muscular responses (Short and Long-Latency Responses, 20-50 ms and 50-100 ms respectively) were preserved or even slightly increased. However, they exhibited perturbation-dependent deficits when stopping and stabilizing their hand in the final target supporting the hypothesis that the tremor was generated by the feedback controller. We show in a computational model that errors in delay compensation accumulating over time produced the same small increase in initial feedback response followed by oscillations that scaled with the perturbation magnitude as observed in ET population. Our experimental results therefore validate the computational hypothesis that inaccurate delay compensation in long-latency pathways could be the origin of the tremor. Significance StatementEssential Tremor origin remains poorly understood. In the present study, we focused on motor impairments associated with feedback control. Following a mechanical perturbation applied to their arm, patients short and initial long-latency stretch responses were preserved. However, we observed clear impairments during the stabilization phase that scaled with the perturbation magnitude. These results were reproduced in a computational model where delay compensation was inaccurate, suggesting that the origin of the tremor may lie in an underestimation of the delays impacting the internal monitoring of the motor commands. Conflict of interestThe authors declare no competing financial interests.

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bioRxiv2023

Dissociable effects of urgency and evidence accumulation during reaching revealed by dynamic multisensory integration

When making perceptual decisions, humans combine information across sensory modalities dependent on their respective uncertainties. However, it remains unknown how the brain handles multisensory integration during movement, and which factors besides sensory uncertainty might influence the contribution of different modalities. We performed two reaching experiments on healthy adults to investigate whether movement corrections to combined visual and mechanical perturbations scale with visual uncertainty. To describe the dynamics of multimodal feedback responses, we further varied movement speed and duration of visual feedback during the movement. The results of our first experiment (N=16, 11 females) show that the contribution of visual feedback decreased with uncertainty. Interestingly, we observed a transient phase during which visual feedback responses were stronger during faster movements. In a follow-up experiment (N=16, 10 females), we found that the contribution of vision increased more quickly during slow movements when we presented the visual feedback for a longer time. Using an optimal feedback control model, we show that the increased response to visual feedback during fast movements can be explained by an urgency-dependent increase in control gains. Further, the fact that viewing duration increased the visual contributions suggests that the brain indeed performs a continuous state-estimation as expected in the optimal control model featuring a Kalman filter. Hence, both uncertainty and urgency determine how the sensorimotor system responds to multimodal perturbation during reaching control. We highlight similarities between reaching control and decision-making, both of which appear to be influenced by the accumulation of sensory evidence as well as response urgency. Significance statementThe exact time course of multisensory integration during movement, along with the factors that influence this process, still requires further investigation. Here, we tested how visual uncertainty, movement speed, and visual feedback duration influence corrective movements during reaching with combined visual and mechanical perturbations. Using an optimal feedback control model, we illustrate that the time course of multimodal feedback responses follows the predictions of a Kalman filter which continuously weighs sensory feedback and internal predictions according to their reliability. Importantly, we further show that changes in movement speed led to urgency-dependent modulations of control gains. Our results highlight connections between motor control and decision-making processes, which both depend on the accumulation of sensory evidence and response urgency.

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bioRxiv2023

Task dependent coarticulation of movement sequences

Combining individual actions into sequences is a hallmark of everyday activities. Classical theories propose that the motor system forms a single specification of the sequence as a whole, leading to coarticulation of the different elements. In contrast, recent neural recordings challenge this idea and suggest independent execution of each element specified separately. Here we show that separate or coarticulated sequences can result from the same task-dependent controller, without implying different representations in the brain. Simulations show that planning for multiple reaches simultaneously allows separate or coarticulated sequences depending on instructions about intermediate goals. Human experiments in a two-reach sequence task validated this model. Furthermore, in co-articulated sequences, the second goal influenced long-latency stretch responses to external loads applied during the first reach, demonstrating the involvement of the sensorimotor network supporting fast feedback control. Overall, our study establishes a computational framework for sequence production that highlights the importance of feedback control in this essential motor skill.

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bioRxiv2023

Impairments of motor adaptation in Essential Tremor are linked to movement execution

0.Essential tremor (ET) is a neurological disorder characterized by involuntary oscillations of the limbs. Previous studies have hypothesized that ET was a cerebellar disorder and reported impairments in motor adaptation. However, recent advances have highlighted that motor adaptation involved several components linked to anticipation and control, all dependent on cerebellum, and the specific alteration of adaptation of ET has not been identified. To address this question we investigated behavioural markers of adaptation in ET patients (n=20) and age-matched healthy volunteers (n=20) in saccadic and upper limb adaptation tasks, probing compensation for target jumps and for velocity-dependent force fields, respectively. We found that both groups adapted their movements to the novel contexts, however, ET patients adapted to a lesser extent compared to healthy volunteers. Importantly, we decomposed movements into components linked to anticipation, preserved here, and real-time execution, which were responsible for the adaptation deficit. Altogether, our results suggest that execution deficits may be a specific functional consequence of the alteration of neural pathways associated with ET. Significance StatementWe tested Essential Tremor patients adaptation abilities in classical tasks including saccadic adaptation to target jumps and reaching adaptation to force field disturbances. Patients adaptation was present but impaired in both tasks. Interestingly, the deficits were mainly present during movement execution, while the anticipatory components of movements were similar to healthy volunteers. These findings reinforce the hypothesis of a cerebellar origin for essential tremor and details the motor adaptation impairments previously found in this disorder.

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bioRxiv2022

Continuous monitoring of cost-to-go for flexible reaching control and online decisions

Humans consider the parameters linked to movement goal during reaching to adjust their control strategy online. Indeed, rapid changes in target structure or disturbances interfering with their initial plan elicit rapid changes in behavior. Here, we hypothesize that these changes could result from the continuous use of a decision variable combining motor and cognitive components. We combine an optimal feedback controller with a real-time monitoring of the expected cost-to-go, which considers target- and movement-related costs, in a common theoretical framework. This model reproduces human behaviors in presence of changes in the target structure occurring during movement and of online decisions to flexibly change target following external perturbations. It also predicts that the time taken to decide to select a novel goal after a perturbation depends on the amplitude of the disturbance and on the rewards of the different options, which is a direct result of the continuous monitoring of the cost-to-go. We show that this result was present in our previously collected dataset. Together our developments point towards a continuous monitoring of the cost-to-go during reaching to update control online and make efficient decisions about movement goal. Author summaryThe way humans perform reaching movements is compatible with models considering that they result from the minimization of a task-related cost function. However, these models typically assume a cost function that does not change within movement, which is incompatible with experimental findings highlighting humans ability to adjust reaching control online and change target flexibly. We hypothesized that this later ability relied on the cost-to-go, which integrates task- and body-related information, being evaluated continuously during movement. We show that this model can optimally select and adjust control during movement in a way that reproduces human behavior in a set of tasks involving change in cost function and change in goal target. Our model predicted that decision-time to change target must be postponed when limb displacements and alternative rewards are smaller, which was borne out in our previous experimental dataset. To conclude, our model explains dynamic updates in reach control and suggests the cost-to-go as decision variable linking decision-making and motor control.

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bioRxiv2022

Different control strategies drive interlimb differences in performance and adaptation during reaching movements in novel dynamics

Humans exhibit lateralization such that most individuals typically show a preference for using one arm over the other for a range of movement tasks. The computational aspects of movement control leading to these differences in skill are not yet understood. It has been hypothesized that the dominant and non-dominant arms differ in terms of the use of predictive or impedance control mechanisms. However, previous studies present confounding factors that prevented clear conclusions: either the performances were compared across two different groups, or in a design in which asymmetrical transfer between limbs could take place. To address these concerns, we studied a reach adaptation task during which healthy volunteers performed movements with their right and left arms in random order. We performed two experiments. Experiment 1 (18 participants) focused on adaptation to the presence of a perturbing force field and Experiment 2 (12 participants) focused on rapid adaptations in feedback responses. The randomization of the left and right arm led to simultaneous adaptation, allowing us to study lateralization in single individuals with symmetrical and minimal transfer between limbs. This design revealed that participants were able to adapt control of both arms, and that adaptation was greater in the dominant arm than in the non-dominant. We also observed that the non-dominant arm showed a different control strategy compatible with robust control when adapting to the force field perturbation. EMG data showed that these differences in control were not caused by differences in co-contraction across the arms. Thus, instead of assuming differences in predictive or reactive control schemes, our data show that in the context of optimal control, both arms can adapt, and that the non-dominant arm uses a more robust, model-free strategy likely to compensate for less accurate internal representations of movement dynamics. Significance statementWe studied a reach adaptation task during which volunteers performed the task with their right and left arm randomly. The randomization of the arms allowed us to study lateralization in single individuals with symmetrical and minimal transfer between limbs. We observed a slightly greater adaptation of the dominant arm in the force applied to counter the perturbation. Moreover, the non-dominant arm showed a more robust control strategy when adapting to the force field perturbation, which enabled similar deviations despite faster movements. These interlimb differences were not caused by differences in co-contraction across the two arms. Our results suggest that both arms can adapt to the presence of a force field but the non-dominant arm uses a more robust, model-free strategy.

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bioRxiv2022

Continuous tracking of task parameters tunes reaching control online

A hallmark of human reaching movements is that they are appropriately tuned to the task goal and to the environmental context. This was demonstrated by the way humans flexibly respond to mechanical and visual perturbations that happen during movement. Furthermore, it was previously showed that the properties of goal-directed control can change within a movement, following abrupt changes in the goal structure. Such online adjustment was characterized by a modulation of feedback gains following switches in target shape. However, it remains unknown whether the underlying mechanism merely switches between prespecified policies, or whether it results from continuous and potentially dynamic adjustments. Here, we address this question by investigating participants feedback control strategies in presence of various changes in target width during reaching. More specifically, we studied whether the feedback responses to mechanical perturbations were sensitive to the rate of change in target width, which would be inconsistent with the hypothesis of a single, discrete switch. Based on movement kinematics and surface EMG data, we observed a modulation of feedback response clearly dependent on dynamical changes in target width. Together, our results demonstrate a continuous and online transformation of task-related parameters into suitable control policies. Significance statementHumans can adjust their control policy online in response to changes in the goal structure. However, it was unknown whether this adjustment resulted from a switch between two policies, or from dynamic and continuous adjustments. To address this question, we investigated whether online adjustments were tuned to dynamic changes in goal target which varied at different rates. Our results demonstrated that online adjustments were tuned to the rate of change in target width, suggesting that human reaching control policies are derived based on continuous monitoring of task-related parameters supporting online and dynamic adjustments.

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bioRxiv2022

Separability of Human Motor Memories during Reaching Adaptation with Force Cues

Judging by the breadth of our motor repertoire during daily activities, it is clear that acquiring multiple motor skills is a hallmark of the human motor system. However, for reaching movements the different planning conditions under which this is possible in laboratory settings have remained a challenging question. Considering the sensitivity of limb afferent feedback relative to externally applied forces, we hypothesised that independent cues delivered by means of background loads could support simultaneous formation of different motor memories of various velocity-dependent force fields. We demonstrate in a series of experiments that indeed healthy adults can form internal priors about opposite force fields, independently of the direction of the background force cue. However, when the cue and force field were only related by their magnitude, a separation was still observed but the associated mechanism was subject to interference. Finally, we highlight that this paradigm allows dissociating trial-by-trial acquisition of internal representations from within-trial feedback adaptation, as these two adaptation mechanisms are associated with different time scales that can be measured reliably. Significance StatementThe conditions under which humans can adapt to different contexts in parallel remain the subject of active debates. Mounting evidence highlights that contextual factors linked to movement planning are necessary to form different motor memories. Here we show that background forces indicative of the direction of a force field could play the role of contextual factors, and enable dual adaptation to different force fields. However, we uncovered that when the cue and the force field were in the same direction but of different magnitudes, the motor memories were still distinct but subject to interference. We further show that different timescales of adaptation observed can be explained by offline and online mechanisms in a model of reaching adaptation and control.

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bioRxiv2021

Reward-dependent selection of feedback gains impacts rapid motor decisions

Target reward influences motor planning strategies through modulation of movement vigor. Considering current theories of sensorimotor control suggesting that movement planning consists in selecting a goal-directed control strategy, we sought to investigate the influence of reward on feedback control. Here we explored this question in three human reaching experiments. First, we altered the explicit reward associated with the goal target and found an overall increase in feedback gains for higher target rewards, highlighted by larger velocities, feedback responses to external loads, and background muscle activity. Then, we investigated whether the differences in target rewards across multiple goals impacted rapid motor decisions during movement. We observed idiosyncratic switching strategies dependent on both target rewards and, surprisingly, the feedback gains at perturbation onset: the more vigorous movements were less likely to switch to a new goal following perturbations. To gain further insight into a causal influence of the feedback gains on rapid motor decisions, we demonstrated that biasing the baseline activity and reflex gains by means of a background load evoked a larger proportion of target switches in the direction opposite to the background load associated with lower muscle activity. Together, our results demonstrate an impact of target reward on feedback control and highlight the competition between movement vigor and flexibility. Significance statementHumans can modulate their movement vigor based on the expected reward. However, a potential influence of reward on feedback control has not been documented. Here we investigated reaching control strategies in different contexts associated with explicit rewards for one or multiple goals, while exposed to external perturbations. We report two strategies: reward could either increase feedback gains, or promote flexible switches between goals. The engagement of peripheral circuits in the modulation of feedback gains was confirmed by the application of a background load that biased feedback vigor directionally, evoking differences in switching behavior in the opposite direction. We conclude that feedback vigor and flexible changes in goal are two competing mechanisms to be selected when interacting with a dynamic environment.

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bioRxiv2021

Fast grip force adaptation to friction relies on localized fingerpad strains

AO_SCPLOWBSTRACTC_SCPLOWHumans can quickly adjust their grip force to a change in friction at the object-skin interface during dexterous manipulation in a precision grip. To perform this adjustment, they rely on the feedback of the mechanoreceptive afferents innervating the fingertip skin. Because these tactile afferents encode information related to skin deformation, the nature of the feedback signaling a change in friction must somehow originate from a difference in the way the skin deforms when manipulating objects of different frictions. To better characterize the origin of the underlying sensory events, we asked human participants to perform a grip-lifting task with a manipulandum equipped with an optical imaging system. This system enabled to monitor fingertip skin strains through transparent plates of glass that had different levels of friction. We observed that, following an unexpected change in friction, participants adapted their grip force within 370ms after contact with the surface. By comparing the deformation patterns when unexpectedly switching from a high to a low friction condition, we found a significant increase in skin deformation inside the contact area arising over 100ms before the motor response, during the loading phase, suggesting that local and partial deformation patterns prior to lift-off are used in the nervous system to adjust the grip force as a function of the frictional condition.

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