Differential cortical activation during saccadic adaptation.

The human saccadic system can dynamically adjust its gain if errors occur after saccade execution. Although this ability has long been studied, the underlying neural mechanisms and its functional purpose remain as of yet unclear. Using functional magnetic resonance imaging coupled with gaze-contingent visual stimulation, we compared brain activation before and after subjects adapted to a gaze-contingent shift in the target location (inward step). This comparison suggests the existence of a predictive signal related to the gain adjustment of upcoming saccades to decrease saccadic gain. Contrary to previous studies, we were able to identify activation differences in the supplementary eye fields that vary with the amount of saccadic gain decrease. In addition to signal amplitude differences in saccade-related eye fields, we also found active cortical regions in the temporal lobe and the posterior insula, which have been functionally related to vestibular processing and to the representation of head position and head motion. The results might point to new directions for research on saccadic adaptation pointing to the functional role of this mechanism.