Interaction of peripheral and cerebellar inputs to red nucleus neurons.

In chloralose anesthetized cats responses of red nucleus neurons to cerebellar cortical or peripheral stimulation are described. Interactions between cerebellar (conditioning) and peripheral (test) stimulations were studied at various interstimulus intervals. Peripheral stimulation alone typically evoked a complex response consisting of an early (15 ms latency) burst, a period of depression of activity (inhibition, lasting up to 300 ms) and a late, long-lasting (on an average 300 ms) excitation. Cerebellar cortical stimulation resulted in a similar pattern of response; but it was composed predominantly of only two phases, an initial inhibition followed by a prolonged late discharge. With conditioning- testing intervals in a range of 10-150 ms, depending on the cell, there was a conspicuous depression of the sh0i.t-latency test excitation, followed by a prominent potentiation of this component. An occlusion of the inhibitory or late excitatory responses occurred when conditioning-testing stimuli were applied with an interval shorter than 0.5 s. It is suggested that the early excitation and the subsequent late components are generated in the red nucleus by independent mechanisms. The initial depression of the early test response is explained as an effect of Purkinje cell inhibition, and the later potentiation as a result of temporary blockage of the cerebellar cortex to afferent input.