SUCCESSIVE ROLES OF THE CEREBELLUM AND PREMOTOR CORTICES IN TRAJECTORIAL LEARNING

THE structures of the human brain engaged during learning of unilatera l trajectorial hand movements were mapped by measurements of regional cerebral blood flow. Trajectorial movement velocity accelerated modera tely after short-term training p < 0.025 and increased further after l ong-term training p < 0.01. During the early phase of learning there w as a significant activation p < 0.001 of the ipsilateral dentate nucle us. By contrast, after overlearning the premotor cortical areas in bot h cerebral hemispheres were maximally activated p < 0.001, while the d entate nucleus was no longer activated. It is suggested that learning of new movement trajectories involves the cerebellum, while overlearne d trajectorial movements engage the premotor cortex.