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

BackgroundSequential 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). ObjectivesThe aim of this study is to evaluate the sequential working memory in patients with YOPD. MethodsSixty-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). ResultsThe 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. ConclusionsThese 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.