Objective: To determine the interactions between dopamine, Working Memory(WM) and Attentional Control(AC) in Parkinson’s disease(PD) patients.

Background: WM impairment is common in PD. Studies have shown a differential effect of dopamine on WM, where low WM PD patients improve with dopamine replacement and those with high WM worsen(i.e. an Inverted-U model). AC, the ability to attend to and encode relevant information, is crucial for WM. Studies suggest WM deficits in PD are due to both reduced storage capacity and an impaired ability to filter irrelevant information. Thus, the interaction between dopamine and WM is confounded by a possible effect of dopamine on AC. Therefore, we aimed to determine the interaction between WM, AC, and dopamine in PD.

Methods: We studied 36 PD patients ON and OFF dopaminergic meds and 29 age-, gender- and education-matched healthy controls(HC). Using a Sternberg task, participants encoded 5 numbers, maintained them during a delay, and responded whether a single probe matched an item from the memory set. To isolate AC from WM, we incorporated trials with and without letter Distractors(D, ND) during the encoding phase.

Results: 8 PD and 9 HC were excluded due to performing at chance levels. We first analyzed distractibility(Accuracy on D vs ND) within each group(paired t-test). We found HC performed similarly on D and ND trials(p=.89) while PD, both ON and OFF meds, trended towards worse Accuracy on D trials(p=.066, p=.073). To investigate a possible Inverted-U effect of dopamine, we divided our PD cohort into High and Low WM using the WM section of the MoCA; High WM = 6/6(n=19) and Low WM < 6/6(n=9). We used a mixed measures ANOVA; within-subject factors of Dopamine(ON, OFF) and Distractors(D, ND), and between-subjects factor Baseline WM(High, Low). We found a Main effect of Distractors(p=.019) and an Interaction effect of Dopamine, Distractors, and Baseline WM(p=.025). Post-hoc t-tests further revealed that dopamine affected High and Low WM groups differently. Specifically, High WM PD had worse Accuracy on D than ND trials ON meds(p=.043), but not OFF(p =.76). By contrast, Low WM PD had worse Accuracy on D than ND trials OFF meds(p=.04), but not ON(p =.84).

Conclusions: Our findings reveal an interaction between dopamine and attention in PD. Notably, the effect of dopamine on AC appears to depend upon a patient’s baseline WM capacity, with High WM individuals becoming more distractible ON dopamine.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/attention-and-dopamine-increased-distractibility-in-parkinsons-disease/