Lower delayed but comparable working memory performance in patients with Parkinson disease

IntruductionThe present study examined nature of memory deficits and its associations with MRI structural metrics in patients with Parkinson disease (PD). MethodsNineteen PD and 23 matched controls underwent two memory experiments. In experiment 1 (delayed memory task), subjects were asked to remember an array of colored rectangles with varying memory set sizes [Low-Load (2 items), Low-Load with distractors, & High-Load (5 items)]. After a 7s delay period, they reported whether the orientation of any relevant figures had changed (test period). In experiment 2 (working memory task), memory arrays were presented in varying set sizes (2 to 6 items) but with no distractors and they were followed by a 2s delay period and subsequent test period. Brain MRI data were acquired to assess morphological differences (volumes and cortical thickness) in brain areas related to attentional filtering (middle frontal gyrus and basal ganglia) and memory storage and consolidation (intraparietal sulcus and medial temporal corticies). ResultsCompared to controls, PD patients had lower memory capacity scores in all memory conditions for the experiment 1 (p <0.021) whereas there were no memory score group differences in any memory set sizes for the experiment 2 (p>0.06). In addition, there were no group differences in structural metrics for any ROI and no asccociations of strucrutal metrics with delayed memory scores (p>0.056). DiscussionThe present findings suggest that both lower attentional filtering and memory storage may contribute to lower delayed memory scores in PD. Memory storage capacity for visuospatial working memory in PD, however, appeared to be comparable to that of controls at least in the absence of apparent distractors. In addition, lower delayed memory in PD may partly be associated with early brain structural or functional changes that may occur before morphological changes.