Mechanoreceptive submodality channel interactions: single unit analysis of afferent inhibition in the primary somatosensory cortex of the cat

Abstract

This study examined whether afferent inhibition generated by activation of one mechanoreceptive submodality influences the response of neurons of the other submodality tested. Response properties of quickly adapting hair and Pacinian neurons in primary somatosensory cortex of the cat were evaluated to assess afferent inhibition generated by single-cycle sinusoidal mechanical stimuli. Animals were lightly anesthetized with sodium thiopental. Stimulation at 20 Hz (low-velocity stimulus) was used to activate hair cells, the receptive fields of which were located in the skin; stimulation at 200 Hz (high-velocity stimulus) was used to activate Pacinian cells, the receptive fields of which were located in the deeper tissues. The skin was partially dissected from the deeper tissue in order to uncouple mechanically the effective receptive surfaces and to achieve greater selectivity. Hair and Pacinian cell test responses were paired with single-cycle 20 and 200 Hz conditioning stimuli. A 20 Hz stimulus, more effective in activating hair cells than Pacinian cells, strongly inhibited the test response of hair cells only and a 200 Hz stimulus, which is more effective in activating Pacinian cells than hair cells, markedly inhibited the test response of Pacinian cells only. Our data indicate that afferent inhibition generated by activation of one submodality channel is largely confined to that submodality channel and is not distributed to the other.