Objective:

To investigate short-term changes in saccade performance associated with repeated performance of oculomotor tasks in various neurological disorders and to elucidate the underlying neural mechanism

Background: Saccade performance undergoes systematic variation with oculomotor task repetition and mixing. The change in performance may reflect the functional modulation of the oculomotor system, both including the cortical and subcortical areas, but the responsible neural mechanism is unknown

Methods: Patients with various neurological disorders were studied, including focal brain lesions (35 cases), cerebellar ataxia (26 cases), and parkinsonism (70 cases). The patients performed two blocks each of the visually guided saccade (VGS) and memory guided saccade (MGS) tasks, in an alternate order (VGS-MGS-VGS-MGS). One block consisted of 25 trials. Each trial started when the subjects fixated the central fixation spot. The VGS task required the subjects to saccade on appearance of a peripheral target, presented randomly to the left or right of it, while at the same time the central fixation point was extinguished. The MGS task required the subjects to make a saccade to the remembered location of target, indicated by a brief flash of light (“cue”) which was extinguished shortly afterwards. The subjects were required to make a saccade on disappearance of the central fixation point. The performance was compared with those of 50 age-matched control subjects. We measured the latency, amplitude and peak velocity of saccades in each trial. For MGS, the ability to inhibit unwanted reflexive saccades was also measured.

Results: In normal subjects, VGS latency in the second block was longer than that in the first block, whereas MGS latency was shorter in the second block than in the first. Overall, the same trend was noted for neurological patients, except that the prolongation of VGS latency in the second session was not observed in patients with focal lesions in the parietal cortex to the posterior limb of the internal capsule. Patients with parkinsonism did not show the shortening of MGS latency in the second block.

Conclusions: The changes in oculomotor performance may result from the short-term functional modulation of the oculomotor system. The lack of this modulation may suggest abnormal function of the system caused by the respective pathology.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/changes-in-saccade-performance-with-oculomotor-task-repetition-in-neurological-disorders/