EEG activity related to preparation and suppression of eye movements in three-dimensional space

Eight normal subjects made visually guided eye movements to four LED targets placed at two different distances (20 and 70 cm) and on either side (+/-10 degrees ) at 70 cm. Four types of eye movements were elicited: pure saccades, convergence, divergence, and combined (divergent saccades). EEG activity was recorded from 62 electrodes and was aligned to stimulus onset. A negativity peaked after 140 ms and was modulated according to the location of the stimulus in space and the type of movement prepared, mainly in central and posterior cortex. For saccade targets, we confirmed a stimulus-related negativity in the posterior and central cortical area, contralateral to target direction. For convergence and divergence targets, this negativity was bilaterally distributed; convergence targets activated a rather extended cortical network in the central and posterior area, while divergence targets activated a more confined posterior area, spreading ventrally from the occipital cortex. Cortical activity for combined targets was lateralised contralaterally to stimulus direction but its topography resembled more closely that after the divergence stimulus. When observers suppressed the relevant eye movement to the stimulus, EEG activity was enhanced on the right hemisphere, showing the more pronounced effect on the right occipital-temporal and central-parietal electrode sites.