Spontaneous discharge rates of cat cerebellar purkinje cells in sleep and waking

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1. 1. Purkinje cells in the posterior vermian cerebellum, which identified themselves in extracellular micro-electrode recording, showed significant decreases in rate of both simple and comples spike discharge when cats went from waking to synchronized sleep. This result was interpreted as consistent with the rest hypothesis of sleep. Because such decreases in rate appeared to be independent of movement, muscle tone and posture, it seemed unlikely that they were the result of feedback from the peripheral motor components of the behavioral change. The fact that presumed granule cells also decreased in rate during synchronized sleep suggested that a decrease in excitatory drive via the mossy fiber pathway might contribute to the decrease in simple spike rate. The decrease in complex spike rate must also be extra-cerebellar in origin since the climbing fibers originate from cells in the olivary brain stem. In the case of both simple and complex spikes, a decrease in activity of brain-stem reticular neurons could account for the results. 2. 2. During the desynchronized phase of sleep, mean rates of both simple and complex spikes were at higher levels than those in waking or in synchronized sleep. This result was interpreted as inconsistent with the rest hypothesis of sleep. Both kinds of discharge were more frequent at the time of the rapid eye movements and associated phasic activity, but simple spikes also showed a tonic increase in rate that was independent of small movements. The increase in complex spike rate could be entirely accounted for by firing associated with eye movement. Since muscle tone was invariably lower during desynchronized sleep, it would be assumed that the tonic increase in rate of simple spikes was not the result of excitation from spino-cerebellar inputs of muscular origin. An increase in excitatory input from reticular neurons is a likely cause of the observed change in levels of simple and complex spike activity in desynchronized sleep.