Spatial distribution of afferent information to the anterior lobe of the cat's cerebellum.

In the decerebrate cat discharges of Purkinje cells with simple and complex spikes as well as granule cell discharges in the c1-zone of lobules Va, b and c of the cerebellar anterior lobe were analyzed during a passive movement of the cat's forepaw. Penetrations were made 50 micrometers apart along the mediolateral and parasagittal directions, the depth never exceeding 500 micrometers. The response of the Purkinje cells to the climbing fiber input was surprisingly constant, while simple spike responses of the same cells showed a great variability to the same input. The variability between granule cell discharges recorded at a 50 micrometer distance from each other was similar to that of the simple spikes of the Purkinje cell. It is assumed that because of a patchy distribution of excited granule cells, two neighbouring Purkinje cells may receive a different information via their parallel fiber inputs. This difference is considered to be responsible for the great variability of their responses to mossy fiber inputs.