Activation of frontoparietal cortices during memorized triple-step sequences of saccadic eye movements: an fMRI study

To determine the cortical areas controlling memory-guided sequences of sacc adic eye movements, we performed functional magnetic resonance imaging (fMR I) in six healthy adults. Subjects had to perform a memorized sequence of t hree saccades in darkness, after a triple-step stimulus of successively fla shed laser targets. To assess the differential contribution of saccadic sub functions, we applied several control conditions, such as central fixation with or without triple-step visual stimulation, self-paced saccades in dark ness, visually guided saccades and single memory-guided saccades. Triple-st ep saccades strongly activated the regions of the frontal eye fields, the a djacent ventral premotor cortex, the supplementary eye fields, the anterior cingulate cortex and several posterior parietal foci in the superior parie tal lobule, the precuneus, and the middle and posterior portion of the intr aparietal sulcus, the probable location of the human parietal eye field. Co mparison with the control conditions showed that the right intraparietal su lcus and parts of the frontal and supplementary eye fields are more involve d in the execution of triple-step saccades than in the other saccade tasks. In accordance with evidence from clinical lesion studies, we propose that the supplementary eye field essentially controls the triggering of memorize d saccadic sequences, whereas activation near the middle portion of the rig ht intraparietal sulcus appears to reflect the necessary spatial computatio ns, including the use of extraretinal information (efference copy) about a saccadic eye displacement for updating the spatial representation of the se cond or third target of the triple-step sequence.