Objective: Our study designed to (1) measure working memory via verbal Digit Span in Parkinson’s patients without mild cognitive impairment (MCI) (2) determine how dopaminergic medications interact with Digit Span’s performance.

Background: Parkinson’s disease (PD) is a neurodegenerative disease that causes debilitating cognitive deficiencies in addition to motor impairments. Although dopaminergic medications are designed to improve motor symptoms, there is evidence that they also affect cognitive ability in various domains, such as working memory. However, the interaction of dopamine and working memory has been complex. Recent studies have used verbal Digit Span as a tool to study working memory in PD patients and have shown that Digit Span Backward can be used as a screening tool for MCI in PD¹. Also, it can reveal how dopamine affects working memory in PD patients with cognitive impairment. Our goal was to push this finding one step further and reveal how PD affects working memory in the pre-MCI stage.

Method: Initially, 25 PD patients ON and OFF dopaminergic medication, as well as 25 age-matched healthy controls (HCs) performed a Montreal Cognitive Assessment (MoCA) test in which they needed to score above or equal 26, assuring they do not have any cognitive impairment. Consequently, they performed Digit Span Backward and Digit Span Forward ON and OFF dopaminergic medication, while HCs performed these tasks only once.

Results: Digit Span forward successfully identified PD patients from HCs, both ON and OFF medications. PD patients had an improved performance in Digit Span forward compared to HCs. Performance in Digit Span backward was not different between PD patients and HCs. However, we found that dopamine significantly improved performance on Digit Span Backward, but not Forward. When divided the PD patients into Low and high baseline working memory groups, we found this dopaminergic improvement was restricted to the Low but not High baseline working memory group.

Conclusion: This study reveals that PD affects working memory even in the pre-MCI stage and offers evidence that the Digit Span test can be used to measure baseline working memory in this cohort of patients. Furthermore, our study elicited that dopaminergic medication can improve Digit Span based on patients’ working memory baseline and task difficulty.

References: Warden C, Hwang J, Marshall A, Fenesy M, Poston K.The effects of dopamine on digit span in Parkinson’s disease. Journal of Clinical Movement Disorders, 2016 Mar 7; 3:5

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