Impaired Sequential Working Memory in Patients With Young Onset Parkinson's Disease

Background: Sequential working memory refers to the cognitive ability to maintain and/or manipulate a set of ordered representations within a short period. It remains unclear whether sequential working memory is impaired in patients with young onset Parkinson's disease (YOPD).

Objectives: The aim of this study is to evaluate the sequential working memory in patients with YOPD.

Methods: Sixty-three YOPD patients (29 women) and one hundred age- and education-matched healthy controls participated in three well-established sequential working memory tests. The YOPD patients were categorized into akinetic rigid type (PD-ART) and non-akinetic rigid type (PD-NART). Participants were asked to maintain digit sequences in mind in the digit span forward (DST-F) and to maintain and manipulate digit sequences in mind in the digit span backward (DST-B) and adaptive digit ordering tests (DOT-A).

Results: The PD-ART group scored lower and had higher ordering costs (difference between the DST-F and DOT-A scores) than the healthy control group in the DOT-A. Moreover, in the PD-ART group, the daily levodopa equivalent dose for dopamine D2/3 receptor agonists positively correlated with the DOT-A score and negatively correlated with the DOT-A ordering cost, suggesting that patients who took a greater dose of dopamine D2/3 receptor agonists tended to have higher DOT-A scores and lower DOT-A ordering costs.

Conclusions: These results indicated that the impaired sequential working memory may be one of markers of identifying early cognitive impairment in patients with YOPD, especially in PD-ART patients. The dopamine D2/3 receptor agonists can recover this impairment to some extent.