Biology subjects

Chib, V. S.

Publications and source records attributed to Chib, V. S..

10 recordsLinked to original sources

bioRxiv2026

Instrumental-Motor Transfer: The Relative Value of Competing Movement Goals Modulates Implicit Motor Learning

Motor learning depends on the integration of several, often competing signals, including reward and punishment (which guide learning the value of actions via reinforcement learning) and sensorimotor errors (which refine the execution of actions via motor adaptation). If and how these signals interact remains controversial. Here we show that the learned value of actions can fundamentally alter how the motor adaptation system learns from errors. Human participants learned the reward values of different movement targets and subsequently underwent implicit motor learning at those targets. Across several experiments, motor learning was robustly attenuated when it brought the limb toward previously punished movement directions. Moreover, learning was globally suppressed when punished targets were themselves the movement goal. Learning was not reciprocally enhanced when it pushed movements toward previously rewarded directions, revealing a valence asymmetry. Using computational modeling, we present a novel mechanism to explain our effects: the motor adaptation system tunes its error sensitivity according to a movement-specific value gradient. Our findings point to a close interaction between reinforcement learning and motor memory -- a kind of "instrumental-motor transfer" -- where learned action values modulate error-based motor adaptation.

neuroscience↗

bioRxiv2026

Transformations of cognitive maps for sensorimotor control

Adaptive embodied behavior involves transforming structured knowledge about the relationship between environment and action into motor signals, but how these transformations are coordinated across brain networks remain unknown. Participants learned associations between visual cues and isometric exertions that varied in force and duration, forming a two-dimensional cognitive map of a force-time space. During behavior, this force-time space was expressed in several cortical regions using grid-like coding schemes, indicating sensorimotor cognitive maps. Importantly, while mnemonic regions such as the entorhinal cortex maintained an unwarped, task-relevant representation, the primary motor cortex encoded a force-time space distorted by perceived effort during motor execution. Dynamic causal modeling showed inhibitory motor-to-mnemonic coupling that predicted the transformation of effort-weighted motor signals into sensorimotor maps. Furthermore, individual differences in learning and navigating the force-time space independently shaped mnemonic map geometry and perceived effort. These findings demonstrate that sensorimotor cognitive maps emerge from dynamic interactions between motor and mnemonic systems and are shaped by individual differences during the learning and execution of movement.

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bioRxiv2025

Neuromuscular Signals Shape Fatigue and Effort-Based Decision-Making in Humans

Physical fatigue influences our willingness to undertake effortful actions, yet the physiological signals driving this process are not well understood. We created a biofeedback paradigm to distinguish the effects of reduced muscle-force capacity from compensatory increases in neuromuscular activity on effort-based decision-making. Human participants made risky choices about prospective physical effort before and after repeated fatiguing exertions under two biofeedback conditions: force biofeedback, which required increased neuromuscular drive, and EMG biofeedback, which constrained the increase in neuromuscular drive. Both biofeedback conditions led to similar reductions in muscle strength and feelings of fatigue. However, we found that the Force biofeedback condition, which required compensatory neuromuscular activation, produced a significantly greater increase in the subjective cost of effort, thereby altering individuals effort-based decision-making more than EMG biofeedback. These findings demonstrate how muscle physiological processes influence feelings of fatigue and decisions to exert effort. Suggesting that fatigue may consist of separate components that collectively motivate behavior while simultaneously protecting and restoring bodily homeostasis during physical challenge.

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bioRxiv2025

Increased Exertion Variability is Linked to Disruptions in Effort Assessment in Multiple Sclerosis

Accurate assessment of exertion is crucial for determining whether to continue or rest during physical activity. Individuals with multiple sclerosis (MS) often report fatigue and motor impairments, yet the mechanisms underlying their assessments of effortful exertion remain poorly understood. Recent work with healthy individuals suggests that motor variability can distort judgments of effort; however, this relationship has not been explored in individuals with MS. In this study, we investigated how variability in physical exertion affects effort assessment in individuals with MS compared to healthy participants. We had participants exert varying levels of physical effort and retrospectively assess the effort they exerted. Individuals with MS exhibited increased exertion variability and tended to overreport their levels of exertion compared to healthy participants. Increased exertion variability was associated with less accurate effort assessment, and this effect was more pronounced in individuals with more advanced MS. These results suggest a possible mechanism through which motor variability may be associated with inflated perceptions of effort in MS, highlighting a potential account of why efforts feel particularly costly to those individuals living with MS and identifying a promising target for treatment and rehabilitation.

neuroscience↗

bioRxiv2025

Striatal and cerebellar interactions during reward-based motor performance

Goal-directed motor performance relies on the brains ability to distinguish between actions that lead to successful and unsuccessful outcomes. The basal ganglia (BG) and cerebellum (CBL) are integral to processing performance outcomes, yet their functional interactions remain underexplored. This study scanned participants brains with functional magnetic imaging (fMRI) while they performed a skilled motor task for monetary rewards, where outcomes depended on their motor performance and also probabilistic events that were not contingent on their performance. We found successful motor outcomes increased activity in the ventral striatum (VS), a functional sub-region of the BG, whereas unsuccessful motor outcomes engaged the CBL. In contrast, for probabilistic outcomes unrelated to motor performance, the BG and CBL exhibited no differences in activity between successful and unsuccessful outcomes. Dynamic causal modeling revealed that VS-to-CBL connectivity was inhibitory following successful motor outcomes, suggesting that the VS may suppress CBL error processing for correct actions. Conversely, CBL-to-VS connectivity was inhibitory after unsuccessful motor outcomes, potentially preventing reinforcement of erroneous actions. Additionally, interindividual differences in task preference, assessed by having participants choose between performing the motor task or flipping a coin for monetary rewards, were related to inhibitory VS-CBL connectivity. These findings highlight a performance-mediated functional network between the VS and CBL, modulated by motivation and subjective preferences, supporting goal-directed behavior.

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bioRxiv2024

Neural mechanisms underlying the effects of cognitive fatigue on physical effort-based decision-making

Fatigue is a state of exhaustion that influences our willingness to engage in effortful tasks. While both physical and cognitive exertion can cause fatigue, there is a limited understanding of how fatigue in one exertion domain (e.g., cognitive) affects decisions to exert in another (e.g., physical). We use functional magnetic resonance imaging (fMRI) to measure brain activity while human participants make decisions to exert prospective physical effort before and after engaging in a cognitively fatiguing working memory task. Using computational modeling of choice behavior, we show that fatiguing cognitive exertion increases participants subjective costs of physical effort compared to a baseline rested state. We describe how signals related to fatiguing cognitive exertion in the dorsolateral prefrontal cortex influence physical effort value computations instantiated by the insula, thereby increasing an individuals subjective valuation of prospective physical effort while cognitively fatigued. Our results support the idea of a general fatigue signal that integrates exertion-specific information to guide effort-based choice.

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bioRxiv2024

The Neurobiology of Cognitive Fatigue and Its Influence on Effort-Based Choice

Feelings of cognitive fatigue emerge through repeated mental exertion and are ubiquitous in our daily lives. However, there is a limited understanding of the neurobiological mechanisms underlying the influence of cognitive fatigue on decisions to exert. We use functional magnetic resonance imaging to examine brain activity while participants make choices to exert effort for reward, before and after bouts of fatiguing cognitive exertion. We found that when participants became cognitively fatigued, they were more likely to choose to forgo higher levels of reward that required more effort. We describe a mechanism by which signals related to cognitive exertion in dlPFC influence effort value computations, instantiated by the insula, thereby influencing an individuals decisions to exert while fatigued. Our results suggest that cognitive fatigue plays a critical role in decisions to exert effort and provides a mechanistic link through which information about cognitive state shapes effort-based choice.

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bioRxiv2024

Neural substrates underlying the expectation of rewards resulting from effortful exertion

Decisions to exert effort for reward are often conceptualized as reflecting a trade-off between anticipated benefits and effort costs. However, economic theories propose that valuation is reference-dependent, such that behavior is shaped relative to expected outcomes rather than absolute reward magnitude. Whether reward expectations influence effort expenditure through such reference-dependent mechanisms, and how these computations are represented in the brain, remains unclear. Using an incentivized grip-force task during functional magnetic resonance imaging, we experimentally manipulated reward expectations independently of reward outcomes. Behavioral results showed that effort exertion varied systematically with reward expectations, indicating that individuals evaluated exertion relative to a reference point. Neural activity in the ventral striatum tracked both prospective reward expectations and deviations between expected and realized earnings. Moreover, these neural signals predicted individual differences in reference-dependent modulation of effort. Together, these findings identify ventral striatal representations associated with reference-dependent effort valuation and suggest that reference-dependent computations contribute to motivated behavior. Significance statementDecisions to exert effort are commonly described as reflecting a trade-off between reward and effort cost. However, whether effort valuation is shaped by reward expectations rather than absolute incentives remains unclear. Using functional magnetic resonance imaging and an incentivized grip-force task, we show that reward expectations serve as a reference point that systematically influences effort expenditure. Neural signals in the ventral striatum tracked both reward expectations and deviations between expected and realized outcomes, and these signals predicted individual differences in reference-dependent effort behavior. These findings suggest that reference-dependent valuation contributes to the neural control of motivated action.

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bioRxiv2023

Motivation upregulates the adaptive response in sensorimotor learning

Motivational state plays a critical role in our ability to learn new motor skills; however, the mechanisms by which motivation influences motor learning are poorly understood. Using a motor learning paradigm in which motivation was varied in a trial-by-trial manner, we found that motivation affects learning by upregulating the rate of the adaptive response, increasing individuals speed of learning. This unveils previously unidentified evidence for a mechanism through which motivation shapes error-based motor learning.

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bioRxiv2018

Motor Cortex Excitability Reflects the Subjective Value of Reward and Mediates its Effects on Incentive Motivated Performance

Performance-based incentives tend to increase an individuals motivation, resulting in enhancements in behavioral output. While much work has focused on understanding how the brains reward circuitry influences incentive motivated performance, fewer studies have investigated how such reward representations act on the motor system. Here we measured motor cortical excitability with transcranial magnetic stimulation (TMS) while female and male human participants performed a motoric incentive motivation task for prospective monetary gains and losses. We found that individuals performance increased for increasing prospective gains and losses. While motor cortical excitability appeared insensitive to prospective loss, temporal features of motor cortical excitability for prospective gains were modulated by an independent measure of an individuals subjective preferences for incentive (i.e., loss aversion). Those individuals that were more loss averse had a greater motor cortical sensitivity to prospective gain, closer to movement onset. Critically, behavioral sensitivity to incentive and motor cortical sensitivity to prospective gains were both predicted by loss aversion. Furthermore, causal modeling indicated that motor cortical sensitivity to incentive mediated the relationship between subjective preferences for incentive and behavioral sensitivity to incentive. Together our findings suggest that motor cortical activity integrates information about the subjective value of reward to invigorate incentive motivated performance.\n\nSIGNIFICANCE STATEMENTIncreasing incentives tend to increase motivation and effort. Using a motoric incentive motivation task and transcranial magnetic stimulation, we studied the motor cortical mechanisms responsible for incentive motivated motor performance. We provide experimental evidence that motor cortical sensitivity to incentive mediates the relationship between subjective preferences for incentive and incentive motivated performance. These results indicate that, rather than simply being a reflection of motor output, motor cortical physiology integrates information about reward value to motivate performance.

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