Magnetic source imaging during a visually guided task.

The cerebellum is heavily involved in the control of accurate eye movements. Cerebellar lesions typically results in nystagmus and dysmetria, inability to stop the eyes at the end of a conjugate movement. Up to now, no cerebellar activity has been identified from non-invasive electrophysiological data. Here we report on neuromagnetic signals of eight healthy subjects in association with visually guided horizontal saccades. The signals were averaged with respect to electrically recorded saccade onsets and their topography revealed activation of the cerebellar vermis starting about 30 ms before and peaking about 170 ms after the saccade onset. In darkness, the cerebellar signals, possibly arising from the cerebellum, were suppressed less than the coinciding signals from the posterior parietal lobe.