Wave Form of Cerebellar Evoked Potentials

¹ From the Department of Anatomy, Wayne State University College of Medicine, Detroit, Michigan

Factors responsible for the waveform of the cerebellar evoked potentials have been studied in cats and monkeys. Such factors include: stimulus strength in anesthetized and nonanesthetized preparations; type of nerve or central tract subject to stimulation, integrity of spino-cerebellar tracts, repetitive stimulation, mode of recording (monobipolar, with needle electrodes). The cerebellar evoked potential consists mainly of a diphasic wave positive negative (potential y), which may or may not be preceded by a faster low amplitude positive deflection (x). The early deflection (x) is more often present when foreleg cutaneous nerves are subjected to stimulation, it can however be found occasionally when other nerves of either fore or hindleg are stimulated. Such early deflection is correlated with the arrival of afferent impulses to the granular layer. When the activation of granular layer is not maximal on the free cortex but presumably occurs in those parts buried in the sulci, the early elevations is not recorded from a surface electrode. In this case, which seems to be very frequent, only the main diphasic deflection (y) is present. The latter is entirely due to cerebellar cortical circuits and follows the arrival of the afferent impulses. It is therefore an index of activation of cerebellar neurons brought about exclusively by afferent inflow and certainly can be taken as a tool for mapping such inflow.

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