Interpositus and fastigial unit activity during sleep and waking in the cat.

Fine wire microelectrodes were used to record single unit activity from two of the intracerebellar nuclei, the interpositus and fastigius, during the sleep-waking cycle. The mean rates, interspike interval distributions and patterns of firing as revealed by autocorrelograms, were investigated. For each stage of the sleep-waking cycle and for as many units as possible the constancy of these measures was examined throughout several sleep cycles. Twenty-four interpositus units were recorded throughout at least one complete sleep-waking cycle. The firing rate of these units in paradoxical sleep without REM was equal to that in quiet wakefulness and greater than that occurring during slow wave sleep. The highest firing rates occurred during REM periods. Some interpositus units were found to have apparent eye movement related activity during REM periods but there was no correlation with waking eye movements. Eleven fastigial units were investigated throughout the sleep-waking cycle. At least half of these units were found to have rhythmic bursting activity during paradoxical sleep which did not appear to be tightly linked with REM periods. Fastigial and interpositus units were found to have slow shifts in their 'background' level of firing which occurred independently of the sleep-waking cycle. The results of these experiments are discussed in relation to the known inputs to the nuclei and in relation to previous studies on other groups of neurons during sleep and waking.