Role of cortical inhibition in heterosensory interaction of neurons of the sensomotor cortex of the cat

: Background and evoked neuronal activity of the sensorimotor cortex was studied in cats under chloralose anaesthesia. Click, flashes and shocks applied to the contralateral forepaw were used as stimuli. Paired heteromodal stimuli were presented with interstimulus intervals of 0, 100, 200, 300 and 400 ms. Stimuli of different modality completely or partly blocked the response to the testing stimulus when the interstimulus interval was 100-200 ms. The maximum response to the second stimulus followed 200-300 ms after the first stimulus. To study the intercortical mechanisms of heterosensory interaction picrotoxin (antagonist of inhibitory neurotransmitter) was locally applied to the studied neuron. Picrotoxin application produced reduction of the blocking period after the conditioning stimulus and appearance of a response to the testing stimulus at shorter interstimulus intervals compared with those observed before application. In some cells an increase in the number of spikes in a burst at one interstimulus interval or an even rise in the response at several interstimulus intervals were observed. The question about the role of intracortical inhibitory influences on the mechanisms of heterosensory interaction on neurons of the sensorimotor cortex is discussed on the basis of the obtained data.