Peripheral neural representation of the spatial frequency of a grating moving across the monkey's finger pad.

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Abstract
Responses in the mechanoreceptive afferent fibers innervating the monkey''s finger pads were examined by moving a ridged surface (grating) across the fiber''s receptive field with a specified velocity and applied force. The temporal frequency of the moving grating (stimulus temporal frequency = velocity of moving surface/spatial period) represented the stimulus feature in single field responses; the spatial period of the grating was represented equivocally. Peripheral neural representation of the grating''s spatial period (or spatial frequency) depended on information signalled by the responding fiber population rather than by individual fibers. The 3 mechanoreceptive fiber populations responded differentially to a grating moving across the finger pad. Slowly adapting fibers coded stimulus combinations with a stimulus temporal frequency in the range of 20-60 Hz best; rapidly adapting fiber coded frequencies of 60-200 Hz best; and Pacinian fibers defined stimuli with a high temporal frequency (100-300 Hz) best. Applying the moving grating to the skin with varying radial forces from 20-60 g did not greatly modify the pattern of discharge in the responding fiber populations.