Although the cortical circuitry underlying saccade execution has well been specified by neurophysiological and functional imaging studies, the temporal dynamics of cortical activity predicting the occurrence of voluntary or reflexive saccades in humans are largely unknown. Here, we examined electrophysiological activity preceding the onset of correct (i.e., voluntary) or error (i.e., reflexive) saccades in an oculomotor capture task. Participants executed saccades to lateralized visual targets while attempting to inhibit reflexive glances to abruptly appearing distracters. Since the visual display was identical for both types of saccades, different electrophysiological patterns preceding correct and error saccades could not be explained by low-level perceptual differences. Compared to correct saccades electrophysiological activity preceding error saccades showed significant differences of the scalp electric field and of voltage amplitudes at posterior electrodes. In addition, though error saccades had significantly shorter latency than correct saccades a prolonged topographic configuration of electric potentials prior to error saccades was found ∼120-140 ms following target onset. In agreement with the known asymmetry in hemispheric dominance for spatial attention, distinct electrophysiological patterns were only found for leftward saccades. While error saccades were associated with stronger activity in the right Frontal Eye Field, correct saccades were preceded by stronger activity in the inferior parietal lobule. These findings suggest that selection of the saccade target in a conflicting situation is determined by early top-down biases originating in frontal and parietal cortical regions critical for spatial attention and saccade programming.
Copyright © 2010 Wiley-Liss, Inc.