Objective: To examine EEG functional connectivity (FC) between brain regions during resting wakefulness as a function of cognitive status in PD.

Background: Progressive cognitive decline occurs in many PD patients and is likely to be associated with abnormal communication between distributed brain networks. EEG-based FC may therefore provide a low-cost noninvasive biomarker for cognitive impairment in PD. Measuring EEG during wakeful resting-state is a particularly suitable choice for cognitively impaired individuals.

Method: Patients were recruited from a Movement Disorders Clinic and classified as meeting or not meeting MDS Level II criteria for mild cognitive impairment (PD-MCI, N=25; PD-N, N = 30); there were 27 age-matched healthy controls. EEG from 64 electrodes was recorded during a 10-min resting-wakefulness period (eyes-closed). The surface Laplacian method was used to reduce the effect of volume conduction. FC between pairs of electrodes was estimated by debiased weighted phase lag index (dWPLI) in standard EEG frequency bands to increase connectivity accuracy. Hierarchical Bayesian regressions, accounting for age, sex, and education, were used to examine FC (1) across groups and (2) global cognition score derived from measures across 5 cognitive domains.

Results: In theta, global FC (averaged across all electrodes) was higher by 0.5 (95% credible intervals (CI): 0.02–1.06) in the PD-MCI group than the HC group; The PD-N group had intermediate values with no evidence of a reliable difference to the other groups. Regionally, the increased theta FC in the PD-MCI groups was most evident for the bilateral FC between the posterior and both anterior and central regions. Global FC for theta was negatively associated with global cognition (β=-3.71, 95% CI: -6.94– -0.37). Although group comparisons did not reveal differences for global FC in the alpha band, it was positively associated with global cognition (β=3.09, 95% CI: 0.14–6.09); this association was more prominent between anterior and posterior regions and within the posterior region.

Conclusion: Declining cognition in PD is associated with increased FC for the theta band and decreased FC for the alpha band. Similar to previous findings, these changes are most prominent between frontal and posterior regions rather than localized effects. As a PD-MCI status confers a high risk of conversion to dementia, it would be informative to follow these patients longitudinally.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/resting-state-eeg-functional-connectivity-in-parkinsons-disease/