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Probing somatosensory representations in the cuneate nucleus of awake primates

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? DESCRIPTION (provided by applicant): The cuneate nucleus (CN) of the brainstem receives ascending input from somatosensory afferents that innervate the skin, joints, and muscles as well as descending input from sensorimotor cortex. While the tactile and proprioceptive response properties of primary afferents and of neurons in primary somatosensory cortex (S1) have been extensively characterized, virtually nothing is known of the response properties of CN neurons. Multiple types of cutaneous afferents innervate the glabrous skin of the hand and play different albeit overlapping roles in tactile perception. Tactile afferents exhibit highly patterned, repeatable responses when their receptive fields are touched. Likewise, receptors in muscles and tendons provide signals related to muscle length, length change, and force. Within S1, the properties of neurons have been extensively characterized and are very different from their peripheral counterparts. First, S1 neurons receive convergent input from multiple somatosensory submodalities. Second, neurons in S1 convey high-level, processed information about stimulus features (edge orientation, surface texture, direction of limb movement). Third, S1 responses can be strongly modulated by the behavioral state of the animals. We propose to characterize, for the first time, the response properties of CN neurons in awake primates and assess (1) the degree to which signals from different somatosensory submodalities converge onto single CN neurons; (2) the extent to which the feature selectivity observed in S1 begins to emerge in CN; (3) the degree to which the state-dependence of S1 responses stems from CN. We anticipate that the present study will have important implications for our understanding of somatosensory processing and may inform the development of subcortical interfaces for brain-machine interfaces used to restore somatosensation in patients with spinal cord injury or who have lost a limb.
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