Visuo-motor adaptation during inactivation of the cerebellar nuclei: A preliminary report

The cerebellum is well suited for controlling visually guided movements and for asserting a role in visuo-motor transformations. We are assessing the contribution of the cerebellum to these processes by testing a monkey's ability to adapt to alterations in the visual or motor aspects of a visually guided tracking task during reversible lignocaine of the dentate or interposed nuclei. A rhesus monkey was trained to track a visual target displayed on a computer monitor using a joystick. Motor aspects of the task were altered by increasing joystick gain so that the required arm excursion was reduced while visual inputs remained unchanged (GAIN). Visual aspects were altered by increasing the excursion of the visual display of both target and cursor while the required arm movement remained unchanged (SCALE). Adaptation to the GAIN change was impaired by inactivation of the dentate nucleus but adaptation to the SCALE change was unaffected. Inactivation of the interpositus nuclei affected both tasks but the SCALE change was more severely affected. These results suggest that the cerebellum is involved in visuo-motor transformations and that the visual and motor aspects of adaptation processes may be differentially controlled.