Objective: To investigate the relationship between the asymmetric dopaminergic degeneration and the attentional resources in a group of patients with PD.

Background: In order to bypass the impaired habitual motor-behavioural control, PD patients may exploit the network of goal-directed mode of action. The frontostriatal connections underline this functioning, that is based on attention. Since the cognitive processes are related with dopamine, the asymmetrical degeneration of the dopaminergic system affects differently the right side affected (RPD) and the left side affected (LPD) PD patients.

Methods: 95 early PD patients without cognitive impairment (53 RPD and 42 LPD) underwent four reaction time (RTs) tasks: visual (V) and auditory (A) RTs were assessed to evaluate alertness; Go-NoGo (GnG) and multiple choices (MC) RTs aimed to explore focused and sustained attention. These tasks were performed before and after a 4-week intensive, motor-cognitive rehabilitation treatment (MIRT). UPDRS III and Timed Up and Go test (TUG) were assessed at the enrolment and at the end of MIRT to evaluate the effectiveness of treatment.

Results: Age was 64±10 and 67±9 for LPD and RPD patients, respectively (p=0.33). Males were 57% and 54% respectively (p=0.06). Before MIRT, no differences between LPD and RPD patients were observed in RTs (p=0.20), UPDRS III (p=0,60) and TUG (p=0,38). After MIRT, LPD patients showed a significant reduction in GnG RTs (p=0.04), MC RTs (p=0.05) and V RTs (p=0.02), while A RTs did not change (p=0.25). No changes were observed in RTs tasks for RPD patients. No differences in levodopa-equivalent dosage were found between groups before (p=0.44) and after MIRT (p=0.66). A significant association between improvement in GnG, MC RTs, V RTs and improvements in UPDRS III and TUG was observed in LPD patients (Pearson R ranging from 0.49, p=0.004 for GnG RTs vs UPDRS III to 0.39 p=0.03 for MC RTs vs TUG).

Conclusions: We did not find differences between groups on tasks measuring attention and their executive components. However, after MIRT we observed an improvement in attentive functions only in LPD patients. This is consistent with the concept that the left nigrostriatal system is more susceptible to early degeneration than the right. This lateralization in the left cortico-basal ganglia network could mean an asymmetry in neruoplasticity, providing some insight into the design of new rehabilitative protocols.

References: Verreyt N et al., Neuropsychol Rev (2011) 21:405–424. Classe n DO et al., Brain and Behavior 2016; 6: e00573.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/relationship-between-dopaminergic-asymmetric-degeneration-and-attentional-resources-in-parkinsons-disease/