Observations on cerebrocerebellar evoked potentials in the cat

Abstract The responses elicited in lobuli VI, VIIA, and VIIB of the cerebellar vermis have been studied in cats anesthetized with chloralose following single shock stimulation of auditory and somatosensory cerebral cortical areas. Recorded from the surface, the responses consisted of two main components, a shortlatency (3–6 msec) relatively slow, positive wave, and a long-latency (12–20 msec), sharper, positive deflection. By double shock stimulation, it was shown that the short-latency activity may be blocked selectively, thus indicating that the long-latency deflection was independent of the nervous activity from which the short-latency part of the response originated. When recorded with a penetrating microelectrode, two sharp negative deflections occurred, with maximal amplitude close to the layer of Purkinje-cell bodies. The first interrupted the descending limb of the initial positive wave after a latency of 6 to 8 msec, the second corresponded in time to the sharp, surface positive, long-latency deflection. These two deflections are ascribed to activity in the Purkinje cells. Following conditioning local cerebellar stimulation, the early Purkinje-cell activity was blocked for 60 to 80 msec, whereas the long-latency activity exhibited a short (8 msec) period of subnormality. These results suggest that the Purkinje cells may be excited via two different pathways following cerebral cortical stimulation. The one is presumably an activation by way of the granule cells, which are excited by the afferent mossy fibers. This activity is recorded as the early “Purkinje-cell deflection.” The other is a direct activation of the Purkinje cells by way of the climbing-fiber system. This gives rise to the long-latency component of the cerebrocerebellar evoked responses. Furthermore, single-unit activity exhibiting inactivation responses following cerebral cortical stimulation is demonstrated.