Direct Evidence for Cortical Suppression of Somatosensory Afferents during Visuomotor Adaptation

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Abstract
Upon exposure to novel visuomotor relationships, the information carried by visual and proprioceptive signals becomes discrepant, often disrupting motor execution. It has been shown that degradation of the proprioceptive sense (arising either from disease or experimental manipulation) enhances performance when drawing with mirror-reversed vision. Given that the central nervous system can exert a dynamic control over the transmission of afferent signals, reducing proprioceptive inflow to cortical areas could be part of the normal adaptive mechanisms deployed in healthy humans upon exposure to novel visuomotor environments. Here we address this issue by probing the transmission of somatosensory afferents throughout the course of adaptation to a visuomotor conflict, by recording median nerve somatosensory evoked potentials. We show that early exposure to tracing with mirror-reversed vision is accompanied by substantial proprioceptive suppression occurring in the primary somatosensory cortex (S1). This proprioceptive gating is gradually alleviated as performance increases with adaptation, returning to baseline levels. Peripheral and spinal evoked potentials were not modulated throughout, suggesting that the gating acted to reduce cortico-cortico excitability directly within S1. These modulations provide neurophysiological evidence for flexibility in sensory integration during visuomotor adaptation, which may functionally serve to reduce the sensory conflict until the visuo-proprioceptive mapping is updated.

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