Temporal patterning in simple spike discharge of Purkinje cells and its relationship to climbing fiber activity.

Abstract

The characteristics of the temporal patterning present in the spike train of [cat] Purkinje cells and the relationship between this patterning and the occurrence of climbing fiber inputs to the same neuron were examined. Two different methods were used: the generalized autocorrelation function (GACF). Two classes of Purkinje cell activity were revealed using the standard autocorrelograms. Type 1 pattern was characterized by a strong positive correlation at short lag times, which decayed to base line over periods greater than 50 ms. The type 2 autocorrelation exhibited a positive correlation at short lag times, but, in the simple spike activity, rapidly decayed to base line within 10-15 ms. These 2 types of autocorrelations do not appear in 2 distinct populations of Purkinje cells. Type 1 and type 2 correlograms can be generated by the same cell under different conditions. The use of GACF allowed an examination of the relationship between the occurrence of a climbing fiber input and the patterning present in the simple spike discharge of Purkinje cells. This technique showed the long-duration positive correlation occurring in the simple spike activity of Purkinje cells possessing a type 1 autocorrelogram to occur preferentially in the simple spike activity following a climbing fiber response. This was demonstrated by comparing the GACF of the simple spike activity constructed by triggering on the occurrence of climbing fiber inputs and the GACF of the same simple spike activity constructed by triggering on randomly occurring simple spikes. For those Purkinje cells with a type 2 autocorrelogram, the GACF constructed by triggering on the climbing fiber input did not have a long-duration positive correlation in the simple spike activity following this input. The short-duration positive correlation that was present in these GACF was similar to that observed in the GACF triggered on the simple spike activity of these cells. In some animals the effects of synchronously activating the climbing fiber input to the cerebellar cortex by olivary stimuli were examined. This procedure usually augmented the long-duration positive correlation occurring in the simple spike activity for type 1 autocorrelations and could convert type 2 autocorrelation patterns into type 1. These alterations could occur independent of the effect of the stimuli on the excitability of the cell as determined by poststimulus time histograms (PSTH).