Brain activation related to retrosaccades in saccade experiments.

In saccade experiments, each trial (e.g. prosaccade/antisaccade) is by definition followed by a saccade, which returns the gaze back to the center (retrosaccade). This event can complicate brain-imaging results when using a simple block-design. We used an event-related functional magnetic resonance imaging design involving prosaccades and antisaccades (testsaccades) to examine brain activation associated with retrosaccades. Testsaccades activated visual and oculomotor-related brain areas. During retrosaccades, these areas were less active than during testsaccades. In the supplementary eye fields, the insula, and striatum, the retrosaccades gave rise to negative blood oxygenation level-dependent responses. In the striatum, these negative responses were equal in size to the positive responses of the testsaccades. This could mask brain activity of testsaccades when not taken into account.