In 1979, Brozoski et al first demonstrated that dopamine depletion from the striatum to the prefrontal cortex in monkeys led to severe impairment on a delayed response task. In the clinic, motor symptoms are treated with dopaminergic medications that alleviate the chronic dopamine depletion that defines PD however, the effects of these medications on cognition are still poorly understood. Although cognitive impairment is one of the strongest predictors of quality of life, there are limited treatments targeting PD cognitive symptoms. WM is the ability to hold and manipulate information in short-term storage for task-relevant purposes WM is crucial to many higher level cognitive processes such as learning, language comprehension, and reasoning. One common, early impairment is a working memory (WM) deficit. Parkinson’s disease (PD) patients are at an elevated risk of developing cognitive impairment and dementia. Moreover, it reveals a partial beneficial effect of dopamine on Digit Span in Parkinson’s disease patients. This study provides evidence for Digit Span Backward as a screening tool for working memory impairment in Parkinson’s disease and for its utility in measuring baseline working memory. In a secondary analysis, we found this dopaminergic improvement was restricted to the Low baseline working memory group the High baseline working memory group was unaffected. Combining patients with and without cognitive impairment, we found that dopamine significantly improved performance on Digit Span Backward, but not Forward. Resultsĭigit Span Backward successfully identified mild cognitive impairment in Parkinson’s disease, both ON and OFF medications. All participants were categorized by cognitive diagnosis using level-II consensus criteria. Parkinson’s patients completed Digit Span Backward and Digit Span Forward ON and OFF medications, while healthy controls completed them once. We recruited 64 Parkinson’s disease patients and 22 age-and education-matched controls. Our study seeks to: (1) determine the validity of verbal Digit Spans for detecting cognitive impairment in Parkinson’s disease patients both ON and OFF medications and (2) ascertain the effects of dopaminergic medications on verbal Digit Span. Research indicates that the interaction between dopamine and working memory follows an Inverted-U shaped curve, but the effect of dopamine on Digit Span has not been well studied. Moreover, Digit Span Backward was recently validated as a screening tool for mild cognitive impairment in Parkinson’s disease when participants were medicated. Verbal digit span tasks offer a potentially straightforward and quick assessment of baseline working memory. It is therefore critical for movement disorders physicians to understand the potential dopaminergic effects on working memory when prescribing these medications. However, there is substantial evidence that dopamine also impacts cognition, in particular working memory. Although cognitive impairment is one of the strongest predictors of quality of life, dopaminergic anti-parkinsonian medications are designed to target motor symptoms. Parkinson’s disease patients are at an elevated risk of developing cognitive impairment.
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