2026 Distinguished Career Award Winner

Friday, April 24: 17:00 – 18:00

Abstract

Evolving thoughts on motor cortex

How does the human motor system produce goal-directed movements given multiple feedback pathways: spinal, subcortical, and cortical? This question occupied much of my career. Early on, as a graduate student studying cat locomotion, I viewed motor control through the traditional Jackson/Sherrington hierarchical framework, where supraspinal regions influence the spinal cord, which generates muscle activity. This model is straightforward to simulate using engineering principles. However, during my postdoctoral work on voluntary control in non-human primates, this strict hierarchy seemed less convincing. Primates have corticospinal projections targeting both spinal interneurons and motoneurons, indicating more complex interactions. Later, approaching the problem with optimal feedback control theory, our research emphasized the importance of transcortical feedback for goal-directed actions, with spinal feedback playing a limited role. Still, I found it challenging to explain such shifts in feedback processing across species and behaviors. Modeling multiple parallel pathways often felt speculative, with strong but conflicting views about the dominance of each level. Our recent work offers fresh insight by making one feedback pathway trainable, allowing it to learn the contributions of the other non-trainable pathway—effectively one part of the motor system modeling another. As predicted, increased spinal feedback during mechanical disturbances corresponded with reduced motor cortex activity. This suggests that goal-directed movements arise from the combined contributions of multiple feedback pathways, with transcortical feedback providing motor commands that are the difference between what is generated by subcortical pathways and what is required for goal-directed behaviour.

Abstract

How reward sculpts human movement

Movement, like perception and cognition, is fundamentally shaped by the pursuit of reward. Across species, reward is known to be a powerful modulator of action, guiding action selection, movement invigoration and reinforcing successful behavior. Most work on reward has leveraged decision-making paradigms, in which agents have to learn to select among a discrete number of actions through reinforcement. Yet growing evidence indicates that reward is also instrumental in tasks with richer motor demands, such as motor learning, where individuals refine movement kinematics through practice. Despite the clear potential of incorporating reward into motor rehabilitation, the precise behavioral and neural mechanisms by which reinforcement shapes motor learning remain underexplored.

In this talk, I will first present evidence that specific properties of reinforcement feedback such as its extrinsic value, timing, and the quality of concurrent sensory feedback profoundly influence how humans control, learn, and retain motor skills. I will also discuss the feasibility, efficiency, and constraints of delivering personalized reinforcement in real time during continuous motor control in healthy adults and patients with chronic stroke.

In the second part, I will present work investigating the causal role of the striatum in motor and reinforcement learning, using transcranial Temporal Interference Stimulation (tTIS)—a non-invasive method for deep-brain neuromodulation in humans—in combination with fMRI. In particular, I will discuss data supporting the causal involvement of specific striatal rhythms in reinforcement and sensory-based motor learning, and highlight their possible implications for neuropsychiatric disorders that impact the motor and reward systems. Overall, these results illustrate the breadth of mechanisms by which reward shapes movement and delineate the promise—as well as the potential limitations—of reward-based approaches to motor rehabilitation.