Movement Control
movement control
sensorimotor control, mouvement, touch, EEG
Traditionally, touch is associated with exteroception and is rarely considered a relevant sensory cue for controlling movements in space, unlike vision. We developed a technique to isolate and measure tactile involvement in controlling sliding finger movements over a surface. Young adults traced a 2D shape with their index finger under direct or mirror-reversed visual feedback to create a conflict between visual and somatosensory inputs. In this context, increased reliance on somatosensory input compromises movement accuracy. Based on the hypothesis that tactile cues contribute to guiding hand movements when in contact with a surface, we predicted poorer performance when the participants traced with their bare finger compared to when their tactile sensation was dampened by a smooth, rigid finger splint. The results supported this prediction. EEG source analyses revealed smaller current in the source-localized somatosensory cortex during sensory conflict when the finger directly touched the surface. This finding supports the hypothesis that, in response to mirror-reversed visual feedback, the central nervous system selectively gated task-irrelevant somatosensory inputs, thereby mitigating, though not entirely resolving, the visuo-somatosensory conflict. Together, our results emphasize touch’s involvement in movement control over a surface, challenging the notion that vision predominantly governs goal-directed hand or finger movements.
A balancing act: goal-oriented control of stability reflexes by visual feedback
During the course of an animal’s interaction with its environments, activity within central neural circuits is orchestrated exquisitely to structure goal-oriented movement. During walking, for example, the head, body and limbs are coordinated in distinctive ways that are guided by the task at play, and also by posture and balance requirements. Hence, the overall performance of goal-oriented walking depends on the interplay between task-specific motor plans and stability reflexes. Copies of motor plans, typically described by the term efference copy, modulate stability reflexes in a predictive manner. However, the highly uncertain nature of natural environments indicates that the effect of efferent copy on movement control is insufficient; additional mechanisms must exist to regulate stability reflexes and coordinate motor programs flexibly under non-predictable conditions. In this talk, I will discuss our recent work examining how self-generated visual signals orchestrate the interplay between task-specific motor plans and stability reflexes during a self-paced, goal-oriented walking behavior.
Neural manifolds for the stable control of movement
Animals perform learned actions with remarkable consistency for years after acquiring a skill. What is the neural correlate of this stability? We explore this question from the perspective of neural populations. Recent work suggests that the building blocks of neural function may be the activation of population-wide activity patterns: neural modes that capture the dominant co-variation patterns of population activity and define a task specific low dimensional neural manifold. The time-dependent activation of the neural modes results in latent dynamics. We hypothesize that the latent dynamics associated with the consistent execution of a behaviour need to remain stable, and use an alignment method to establish this stability. Once identified, stable latent dynamics allow for the prediction of various behavioural features via fixed decoder models. We conclude that latent cortical dynamics within the task manifold are the fundamental and stable building blocks underlying consistent behaviour.