Patterns of spontaneous Purkinje cell complex spike activity in the awake rat

The olivocerebellar system is known to generate periodic synchronous discha rges that result in synchronous (to within 1 msec) climbing fiber activatio n of Purkinje cells (complex spikes) organized in parasagittally oriented s trips. These results have been obtained primarily in anesthetized animals, and so the question remains whether the olivocerebellar system generates su ch patterns in the awake animal. To this end, multiple electrode recordings of crus 2a complex spike activity were obtained in awake rats conditioned to execute tongue movements in response to a tone. After removal of all mov ement- and tone-related activity, the remaining data were examined to chara cterize spontaneous complex spike activity in the alert animal. Spontaneous complex spikes occurred at an average firing rate of 1 Hz and a clear appr oximate to 10 Hz rhythmicity. Analysis of the autocorrelograms using a rhyt hm index indicated that the large majority of Purkinje cells displayed rhyt hmicity, similar to that in the anesthetized preparation. In addition, the patterns of synchronous complex spike activity were also similar to those o bserved in the anesthetized preparation (i.e., simultaneous activity was fo und predominantly among Purkinje cells located within the same parasagittal ly oriented strip of cortex). The results provide unequivocal evidence that the olivocerebellar system is capable of generating periodic patterns of s ynchronous activity in the awake animal. These findings support the extrapo lation of previous results obtained in the anesthetized preparation to the waking state and are consistent with the timing hypothesis concerning the r ole of the olivocerebellar system in motor coordination.