Clues to the Pathophysiology of Cognitive Decline in Parkinson’s Disease

Hypothesis

Hypothesis

Hypothesis:
Working memory for objects and working memory for spatial relations have dissociable neural substrates in young healthy participants. This pattern of localization is altered in early Parkinson's disease (PD) because patients have a selective deficit in working memory for spatial relations.

Methods:
The researchers have performed fMRI studies in young healthy participants, patients with PD, and control participants matched to the PD patients in age, sex, and educational level.

Findings:
Healthy older adults and PD patients recruited a left frontoparietal network during performance of the spatial working memory and object working memory tasks, consistent with previous reports. The predominance of left-hemisphere activation suggests that both groups were using a verbal strategy to perform the spatial working memory and object working memory tasks. By this view, phonological working memory operations were recruited to rehearse the location or identity of visual stimuli, and thereby to maintain an on-line representation of specific spatial locations and objects held in memory in posterior parietal cortex. Overall, significant activation in the PD group was less extensive and less robust than that in the CON group, even though the behavioral performance of the two groups did not differ. Perhaps the PD patients were more variable than CON in the particular neural resources recruited to perform the task. For spatial working memory, CON seemed to rely on visuospatial processes localized in posterior parietal cortex. PD patients, however, consistent with their previously documented deficit in spatial working memory, may have resorted to verbal mediation. For object working memory, CON showed greater recruitment of a left frontoparietal network than did PD patients, consistent with previous reports. Low performers, regardless of group membership, recruited a larger neural substrate for both tasks, indicating increased effort or additional strategies.