Multimodal Sensory Modulation and Human Motor Control

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In order to interact in our environment during everyday activities, the central nervous system (CNS) must identify and extract relevant sensory information from a vast array of concurrent inputs from many sources. Such processing is essential for accurately controlling movements, learning new motor skills leading to adaptation in the brain, and successfully relearning movement patterns following brain injury. Sensory inputs initially arrive and are processed at very distinct, modality-specific areas of the brain (cortex) before being integrated in higher-order sensory association cortical areas. Previous research has provided detailed mechanistic information regarding how sensory inputs within a specific modality are represented during movement at a relatively early cortical level. For example, our ongoing research suggests that selection of somatosensory information begins to occur at the very earliest stage of cortical processing, the primary somatosensory cortex, during sensory-guided movement and perceptual discrimination. Highly selective mechanisms appear to be involved, including inhibition of early cortical representations of task-irrelevant, unattended information, with facilitation of task-relevant, attended information. The specific regions that control this selection are unclear, however interactions between multiple brain regions including the prefrontal and parietal cortex, as well as the thalamus and cerebellum appear to play an important role. Much less is known about how these mechanisms of control are altered when the CNS is presented with multiple sources of sensory inputs, as is usually the case during natural movement. Our current work suggests that the cortical representations of competitive visual and tactile (touch) input change substantially depending on the relevance and temporal relationship between the stimuli. As such the proposed research program will focus on developing fundamental understanding of the interactions and integration of sensory inputs from multiple modalities (vision, position sense of the limbs, touch) at a cortical level and the role this plays in the acquisition and control of normal limb movement. Three themes of inquiry are proposed that include experiments to study neural mechanisms of (1) selection of relevant stimuli among multiple sensory inputs, (2) integration of relevant multimodal stimuli, and (3) experience-dependent adaptations in the brain. The themes of experiments in the research program will provide important training opportunities for several trainees, including the use of advanced human electrophysiological technologies to study sensorimotor function. The proposal will inform potential strategies that can enhance the brain's dynamic adaptations to improve motor performance in healthy individuals and strengthen rehabilitation strategies and lessen disability following brain injury.