Relations among climbing fiber responses of nearby Purkinje Cells.

ACIWITY PATTERNS in the cerebellar cortex may be studied by simultaneously recording from two or more cells whose spatial separation and orientation are known. Appropriate statistics such as the cross-correlogram may then be used to describe the temporal relationships. Further computational and experimental methods some times permit an interpretation of the temporal relationships in terms of the underlying anatomical connections (20, 23, 24). Two quite different types of discharges may be recorded from cerebellar Purkinje cells, simple spikes and complex spikes. Simple spikes are similar to nerve impulses recorded elsewhere in the central nervous system and are evoked primarily through parallel fiber activation. Complex spikes have the same sharp initial component, but this is followed by a slow wave lasting 10-15 msec on which ripples or small spikes are superimposed. The complex spike has been shown to be the response of the Purkinje cell to a single spike or a brief burst of spikes in the climbing fiber axon (11), and is also referred to as a climbing fiber response (CFR). In our previous work (6) we found that the simple spikes of nearby Purkinje cells were often correlated in time. It was suggested that the temporal relationship between two such discharges depended on the parallel fiber input shared by the two cells and consequently could be related rather precisely to their spatial separation and orientation on the cerebellar sheet. Freeman (14) has made the same suggestion and provided experimental support for it. The present experiments also used the method of statistically analyzing simultaneous recordings from two or more cells