Processing of somatosensory information in striatum of behaving cats.

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Abstract
Unit activity was recorded from the striatum of behaving, partially restrained cats. The processing of facial somatosensory information in this component of the basal ganglia was assessed. Responsive cells were treated for ability to encode such stimulus parameters as magnitude, location and direction of movement. Of striatal cells 25% were responsive to somatosensory stimuli applied to the face. On the basis of optimal stimulus type, cells could be grouped in 1 of 3 categories: 47% of responsive cells were influenced exclusively by short rise time, short-duration indentation of the skin; 39% were affective exclusively by rapid brushing of the hair or vibrissae, and 14% were influenced by both skin indentation and rapid brushing. Receptive fields varied from moderate in size (e.g., front lower lip) to quite large (e.g., entire face). Most responsive cells (99%) had receptive fields that included some perioral tissue. The probability that a portion of the face would be included in a receptive field increased progressively as the front of the mouth was approached. The majority (73%) of striatal neurons showed no evidence of encoding stimulus magnitude. In the remaining cells, only large changes in stimulus magnitude evoked significantly different changes in firing rate. In contrast, units were highly sensitive to changes in stimulus location. As a stimulus was brought closer to the front of the mouth, it evoked increasingly larger, shorter latency responses. In addition, some cells that were activated by brushing showed most pronounced responses to stimuli that moved toward the front of the jaw or mouth. The sensory properties of striatal neurons suggest that they encode the location of a tactile stimulus with respect to the front of the jaw and mouth. Findings from the clinical, anatomical and electrophysiological literatures indicate a primary basal ganglionic involvement in actions mediated by axial muscles. Facial somatosensory information may be processed by the striatum to influence axial muscles for head-positioning movements.