Interaction of converging peripheral and cerebellar cortical inputs on interpositus neurons of the cat.

Anesthetized and immobilized cats were used. The interval between the peripheral (conditioning) and the cortical (testing) stimulation equalled the latency of the response to effective peripheral input. Efferent nuclear neurons were identified by antidromic stimulations from contralateral brainstem nuclei. Various sequences of excitation and inhibition of different duration were induced by peripheral inputs. Initial excitation was observed in efferent neurons in cases of selective reactions to one of the peripheral stimulations. In some neurons both initial excitation and inhibition were observed. Besides selective reactions, in neurons with background activity a convergence of different peripheral inputs was seen. Responses to converging peripheral influences had usually a similar pattern of PSTH, with the shortest latent period to the dominant afferent input. Effects of cerebellar cortical stimulation were observed in nuclear neurons, both efferent and intranuclear. Effects of cortical stimulation were evoked from a limited area of the stimulated cortical surface; convergence and divergence of influences were observed. Peripheral and cortical stimulations induced various patterns of impulse activity of nuclear neurons. Interaction of converging peripheral and cortical inputs on a nuclear neuron was determined by the level of excitation or inhibition evoked by the peripheral stimulus and the phase of the cortical action (inhibition or "disinhibition"). Besides its participation in integrative processes at the nuclear level, the cerebellar cortex determines the duration and frequency of successive onsets of excitatory bursts at the "output" of the cerebellum, thus playing a decisive role in the coding of information to other structures of the brain.