THE SENSORY GUIDANCE OF MOVEMENT - A COMPARISON OF THE CEREBELLUM ANDBASAL GANGLIA

We used positron emission tomography (PET) to compare the contribution of the cerebellum and basal ganglia to the sensory guidance of moveme nt. In one condition the subjects used a computer mouse to draw a seri es of Lines on a computer screen (DRAW). In the second condition the s ame lines were presented to the subjects, and they had to track the li nes with a mouse pointer on the screen (COPY). In a third condition th e subjects were again presented with the same lines, and they simply f ollowed movements of the pointer with their eyes (EYES). In the fourth condition, the subjects fixated a central point, ignoring the sequenc e of presented lines (FIX). The pens and cerebellum were activated mor e during visually guided tracking than in freely generated drawing (CO PY vs DRAW). The basal ganglia were activated equally in both DRAW and COPY. The prefrontal and inferior temporal cortex were activated more when subjects drew lines freely (DRAW) than when they copied them (CO PY). We conclude that the cerebellum is specialized for using sensory information to correct movements, but that the basal ganglia are invol ved both in movements that are self-generated and in movements that ar e guided by external cues.