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Predicting the timing of motor commands in a synchronization task: a PET study

We used positron emission tomography to examine the neural substrate underlying self-initiated (SI) versus externally triggered (ET) synchronized movements. Seven healthy subjects performed synchronized right hand and foot movements in SI and ET conditions. Behaviourally, subjects exhibited a precession of finger initiation over foot dorsi-flexion in the ET condition, and precession of foot over finger onset in the SI condition. When compared to ET movements, the preparation of SI synchronized movements showed activation of the dorsolateral prefrontal cortex, pre-supplementary motor area and lateral premotor cortex. These cortical regions were thought to be associated to the internal movement triggering for the dorsolateral prefrontal cortex and to the motor preparation for both pre-supplementary motor area and dorsal premotor cortex. Our main finding was a prominent activation of the left posterolateral hemi-cerebellum in the SI condition when compared to the ET condition. These results provide anatomical data supporting the timing and predictive roles of the cerebellum in motor control.