Abstract

Mechanisms of spatial working memory and eye movement control were investigatedin eight mild to moderate Parkinsons disease patients (PDs). Subjects were presented with asequence of four targets which had to be memorized and then recalled by moving their eyes tofixate the four locations in the correct order. Two variations on this procedure were used inwhich either a different sequence of lights was presented on each trial, or an identical sequenceof lights was repeated on each trial. In both conditions subjects made memory-guided eyemovements in the dark, without any visual cues to eye movement accuracy or the locations of thepreviously illuminated lights. Analysis of the amplitude of the primary eye movement and finaleye position for each step in the sequence showed that PDs made several discrete saccadic eyemovements of reduced amplitude before reaching the final eye position (multi-stepping). When anovel target sequence had to be memorized on each trial, the final eye position reached by PDsfor each location was also found to undershoot relative to controls. In contrast, when an identicalsequence of targets was repeated on each trial, PDs final eye position was found to be normal,although primary movement amplitudes were still reduced. PDs showed no multi-stepping andnormal final eye position gain under conditions for which the target lights in the sequence wereilluminated during movement execution. PDs also made an increased proportion of overt errorsin target sequence recall. Parallel neuropsychological testing in PDs and controls revealed thaterror rates in the sequential memory-guided saccade task were significantly correlated withperformance in a task thought to be sensitive to spatial working memory dysfunction. Thefindings suggest that short-term spatial memory representations are disrupted in the early stagesof PD. Copyright (C) 1998 Elsevier Science B.V.