On the origin of the climbing fibres of the cerebellar cortex.

Unitary climbing fibre activity has been systematically recorded in the rabbit cerebellar cortex at the level of the Purkinje cell layer every 100 micron along the longitudinal axis of the folium. In one group of animals, spontaneous activity was identified in 197 out of 204 (96.6%) explored layers, and was uninterruptedly present up to 2,400 micron along the folia. In a second group of animals, stimulating electrode were placed in the inferior olive and it was found that spontaneous or evoked climbing fibre activity was absent in only 19 out of 422 explored layers: 377 (89.3%) showed a spontaneous and 396 (93.8%) a short latency evoked activity. If some limitations of the method are considered, it can be concluded that all Purkinje cells receive climbing fibre innervation from cells of the inferior olive. The present experiments support the conclusion that the inferior olive is the unique source of climbing fibres.