Interaction of extracerebellar and cerebellar cortical inputs in dentate neurons of the cat.

Interaction of afferent influences from pontine nuclei (NRTP, NPL and NPM) and inferior olive (IO) with influences from the cortex of neocerebellum (Crus I and II of hemisphere) was studied in dentate neurons (ND) in anesthetized and immobilized cats. Interaction of converging influences was tested with regard to response latencies. Activation of pontine nuclei (NP) and IO as well as cerebellar cortex affected all varieties of nuclear neurons regardless of their localization within the nucleus and their type (efferent or intranuclear). Stimulation of precerebellar nuclei (NP and IO) evoked in ND neurons an activity similar in firing patterns, displayed as bursts of excitation (S + S) lasting up to 10 ms. Initial excitation with following inhibition (S+-S), or excitation changed into inhibition with "rebound" [S+ - +(2)S] were also observed. Similar patterns of evoked activity were in neighboring nuclear neurons. Stimulation of lateral parts of Crus I and Crus II was most effective for ND. Influences from different parts of stimulated cortex have points of maximal action onto the given nuclear neuron (discrete action); divergence and convergence of influences were also observed. Cerebellar cortex stimulation depressed background impulse activity of ND neuron with gradual return to an initial level (S-S) or through a "rebound" [S- + (2)S]. Interaction of cortical and precerebellar nuclei influences was determined by algebraic summation of excitatory and inhibitory converging actions and the spontaneous activity. The latter persistently decreased in the course of repeated stimulation of the cerebellar cortex. The data show some peculiarities of that interaction and the role of the nuclear activity proper in forming the signals at the "output" of the cerebellum.