RETINOTOPIC AND DIRECTIONAL DEFICITS OF SMOOTH PURSUIT INITIATION AFTER POSTERIOR CEREBRAL HEMISPHERIC LESIONS

We investigated the initiation of ocular smooth pursuit with horizontal ramp targets in 16 patients with unilateral posterior cerebral lesions. Four of the 16 patients had directional pursuit asymmetry, in which smooth eye movement velocities were reduced toward the lesion, independent of target location on the retina. Of seven patients with normal visual fields for the target, two had a retinotopic eye movement deficit consisting of impaired smooth pursuit of targets moving in both horizontal directions in the hemifield contralateral to their lesion. Patients with retinotopic deficits and normal visual fields, and those with directional deficits, had impairment of smooth pursuit similar to that caused by unilateral lesions of cortical areas MT (middle temporal) and MST (medial superior temporal) in monkeys. All but one patient with either of these defects had a lesion near the junction of Brodmann's areas 19, 37, and 39, providing evidence that this region includes the human homologues of monkey areas MT and MST. One patient with a retinotopic pursuit defect and normal visual fields had a lesion of the rostral superior temporal sulcus, which may have included the homologue of the superior temporal polysensory area of monkeys.