Effects of cerebellectomy on the cat's vertical vestibuloocular reflex.

The effects of cerebellectomy on the semicircular canal evoked responses recorded from individual vertical and oblique eye muscles were studied in cats anesthetized with Ketamine. The phase lag relative angular acceleration of the electromyographic response was consistently smaller over the frequency range tested (0.02--1.0 Hz) in cerebellectomized than in intact animals. This finding indicates that the time constant of the central, neural integrator was shifted towards smaller values by the lesion. This was also suggested when the vertical eye movements generated by rotation about the pitch axis were recorded in the fully alert animal. In addition, the EOG data show that the phase of the VOR in the low frequency range was not altered following cerebellectomy suggesting that the macular influences were still present. When the EMG responses of the superior oblique (SO) and superior rectus (SR) muscles were studied in their presumed main mode, i.e. roll-canal and pitch-canal, respectively, no difference was noted in hemicerebellectomized animals when compared to intact control animals. However, when SO and SR were studied in pitch-canal and roll-canal rotation, respectively, dramatic changes in the response pattern were noted in lesioned animals.