Afterdischarges elicited by electrical thalamic stimulation in the hemicerebellectomized baboon

Electrical stimulation of the ventrolateral (VL) nucleus of the thalamus was performed on hemicerebellectomized baboons. Stimulation was delivered in volleys of 40 to 60 Hz lasting 5 to 25 sec, and at intensities ranging from 1 to 6 mA (width of shock 0.5 to 5 msec). Similar parameters of stimulation produced asymmetrical motor and electrocortical responses. When the normal VL nucleus was stimulated, these responses were tonic or tonic-clonic. When the VL nucleus deprived of its cerebellar afferents was stimulated, the tonic-clonic responses were followed by afterdischarges appearing in the EEG which persisted after cessation of stimulation. The role of the cerebellum in the lowering of the excitability threshold of some structures, particularly the VL nucleus, is discussed, as are the systems likely to play a role in producing various clinical responses.