Steady potential of cerebellar cortex. Results of direct, olivo- and ponto-cerebellar activation

Abstract

Evoked responses were recorded from cerebellar cortex in 68 cats. Surface records were compared with those from graded depths of penetration. Potentials were either evoked directly by surface stimulation or by stimuli applied to the inferior olive or pericruciate cortex for activation of the cerebro-ponto-cerebellar path. Single stimuli and 1 sec trains at 6/sec and 20/sec were used. As evoked by a single shock, the early component of each record shows a somewhat different configuration but is usually diphasic in character. With vertical penetration of cortex this early diphasic potential inverts at 0.3–0.4 mm, corresponding to the position of Purkinje cell somata. All such records also show a slow negativity which follows upon the early diphasic complex. Upon repetitive stimulation the slow components summate to produce a prolonged negative shift which significantly outlasts the stimulus period. Such shifts also reverse to positive upon penetration of the electrode below the level of the Purkinje somata. The evidence suggests that the shift is principally a summation of the slow negativities which are attributed to EPSPs arising along the Purkinje dendritic arborization. Differences were noted between the olivocerebellar responses of vermis and paramedian lobule, the latter being closely akin in form and dispersion to that which is seen in the cerebro-ponto-cerebellar activation. Convulsive activity was elicited from stimulation of the two afferent sources, but not from stimulation at the cerebellar surface. These discharges were relatively prolonged (about 10 min), showed a significant post-ictal depression, and were notable for the magnitude of the negative SP shift which accompanies the train of convulsive discharge.