Converging eye movements evoked by microstimulation of the fastigial nucleus of macaque monkeys

Stimulation of the dorsal part of the fastigial nucleus in macaques is known to evoke ipsilateral saccades, while those of the ventral part produce contralateral saccades. It was found that stimulation of the transitional zone moved the visual axis (eyes) to converge at an area (focus) in the oculomotor range, regardless of the initial eye position. These saccades were designated as ‘converging saccades’. Converging saccades were directed to the focus, but the eyes did not attain the focus in one motion. Only the repetition of stimuli brought the eyes near the focus. When stimulation is applied to the transitional zone at progressively more ventral sites, the focus gradually shifted, starting from the ipsilateral hemifield to the contralateral hemifield by taking various routes.