Postsynaptic responses of motor cortex neurons of cats to sensory stimulation of different modalities.

In the last few years the processes underlying the multisensory convergence at the cortical level have been studied by many authors (3, 5, 6, 15-17). It is well known that light chloralose narcosis enables revealing the responses of the motor cortex neurons to sensory stimulations of hfferent modalities (1, 5-7, 10, 15-1 7). So far, the synaptic mechanisms of these reactions have remained obscure, especially those in response to activation of nonspecific afferent inputs (16). Some advance has been made only in the analysis of effects of electrical and natural stimulation of skin and extremity Perves (1, 2, 6, 10, 11, 17). The present paper is devoted to the description of the PSP's of neu-rons of the cat motor cortex in response to the stimulation of different mlodalities: flashes of 50 msec duration and 0.3 J intensity, clicks of 0.5 msec duration and 70 db intensity and electrical shocks produced by rectangular pulses of 0.5 msec duration and suprathreshold intensity. Electrical shocks were applied to the sole of a contralateral forepaw by means of needle electrodes. Acute experiments were performed in 26 cats weighing 2.5-3.8 kg. The animals were operated under mixed anesthesia (35-45 mg!kg a-chlo-ralcse + 15 mgikg pentobarbitone) administrated i.p. and immobilized by d-tubocurarine or diplacine, administrated i.v. as needed. Intracellu-lar recordings were obtained laterally in the anterior and posterior sig-moid gyri. The microelectrodes were filled with 2M potassium citrate solution according to Tasaki and co-workers (14). The stimulations with polarizing current were performed with a bridge-circuit (4). A bipolar