Spatial and temporal features of afferent inhibition of thalamocortical relay cells.

1. The temporal and spatial features of the afferent inhibition of thalamocortical relay (TCR) cells in the ventrobasal complex of the thalamus have been examined using paired conditioning and test air jets. 2. The response of TCR units to air jets may be divided into three parts: a) an early response of 1--6 impulses, which begins after a latency of 8--10 ms and lasts for 10--25 ms; b) a period of 70--80 ms following the early response, during which the spontaneous activity is inhibited; and c) a period of late activity, which follows the inhibitory period. 3. The inhibition of TCR units generated by an air jet lasts about 80 ms. The time course of inhibition is the same in hair units and in units activated by Pacinian corpuscles. Evidence is presented that suggests that inhibition decays at the same rate throughout the inhibitory receptive field. 4. The spatial features of inhibition demonstrated in this study are: a) that the excitatory and inhibitory receptive-field centers coincide; b) that these fields have different shape; and c) that there is a significant area in which the inhibitory receptive field surrounds the excitatory receptive field.