[Electrophysiologic study of conduction of afferent impulses through the medial geniculate body]

In experiments carried out on cats immobilzed with d-tubocurarine 280 neurons located in pars principalis of the medial geniculate body and 408 auditory cortical neurons located in AI were studied extra- and intracellularly in response to stimulation of the brachium of the inferior colliculus and geniculocortical fibres. It was shown that the initial stage of the reaction observed in the medial geniculate body neurons response to stimulation of the brachium of the inferior colliculus continue for 13.0 ms. Excitation of 72% of neurons participating in the reaction occurs during the first 3 ms after stimulation. 84% of IPSPs arouse in the same period of time. It is found that some medial geniculate neurons have axons entering the inferior colliculus. Substantial part of fibres in the brachium of the inferior colliculus comes to the auditory cortex without synaptic switching in the medial geniculate body. 76% of medial geniculate neurons from the group excited monosynaptically are thalamocortical relay neurons and the rest are interneurons. 90% of relay neurons in the medial geniculate body are excited monosynaptically. Many medial geniculate neurons respond to stimulation of the brachium of the interior colliculus by EPSP-IPSP sequence or by primary IPSPs. About 20% of primary IPSPs develop monosynaptically. The maximal amount of IPSPs comes into being disynaptically with the participation of inhibitory interneuron located at the input to the medial geniculate body. The inhibition observed in this case is direct afferent one.