Simple spike firing patterns of cat cerebellar purkinje cells in sleep and waking

Abstract

1. 1. Previous studies of neuronal activity during sleep have indicated that the pattern of firing of neurons was altered as a function of behavioral state (waking, synchronized sleep and desynchronized sleep). Although not evaluated quantitatively, this change in pattern has been assumed to be independent of changes in firing rate and has formed the basis for postulates of physiological mechanism (such as disinhibition) acting differentially in sleep. In a population of identifiable units, we have examined quantitatively the relationship between firing pattern (as measured by interspike interval histograms and by auto-correlation techniques) and firing rate to see if alterations in firing rate could explain differences in firing pattern observed during behavioral state changes. 2. 2. Simple spikes of 39 Purkinje cells in the cerebellar vermis were recorded by extracellular micro-electrodes during natural sleep and waking in unrestrained, unanesthetized cats. 3. 3. An analysis of covariance demonstrated that characteristics of the form of interspike interval histograms (variance, third moment, fourth moment, percentage of intervals at the mode) were a function of the firing rate of the unit. All units firing with the same mean interspike interval duration tended to have the same histogram form; behavioral state was not an important determinant of histogram form except insofar as the unit firing rate was altered. 4. 4. Auto-correlation analysis demonstrated a tendency toward rhythmic firing with period duration near the modal interval. A high degree of rhythmicity was associated with a high firing rate, and a low degree of rhythmicity was associated with a low firing rate, suggesting that this aspect of firing pattern, like that of histogram characteristics, was also a function of firing rate. 5. 5. These findings indicate that, for simple spikes of cerebellar Purkinje cells, changes in firing rate account for differences in firing patterns observed with behavioral state changes.