Event‐Related Delta Oscillations are Diminished in Parkinson’s Disease with Different Cognitive Status: A Longitudinal EEG Study

Abstract

AbstractBackgroundThe neurophysiological differences between Parkinson’s disease mild cognitive impairment (PD‐MCI) and cognitively normal Parkinson’s disease (PD‐CN) have been poorly understood, covering limited electrophysiological interpretation. Delta event‐related oscillations (ERO) are recognized as a useful electrophysiological indicator of cognitive decline (Güntekin et al., 2018; Yener et al., 2019). The aim of the present study was to investigate baseline and follow‐up delta EROs of individuals with PD‐CN and PD‐MCI in comparison with healthy controls (HC).MethodsThirty one PD‐CN, 23 PD‐MCI, and 30 demographically‐matched HC were included. All examinations were applied to participants in a time period of 12.50±0.80 months. A comprehensive neuropsychological test battery was used for the PD‐MCI classification (Litvan et al., 2012). EEGs were recorded during visual oddball paradigm. The maximum peak‐to‐peak event‐related delta (0.5‐3.5 Hz) responses of the groups to the target stimulus were measured. Repeated measures ANOVA included Group (3 levels: HC, PD‐CN, PD‐MCI) as a between‐subject factor, Time (2 levels: baseline, follow‐up), and Anterior‐Posterior Electrode Location [AP (6 levels: frontal, central, temporal, temporoparietal, parietal, occipital)] as a within‐subject factor.ResultsThere was an interaction effect for Group x Time on event‐related delta responses [F(2,81)=3.650, p=0.030], indicating follow‐up delta EROs were reduced only in PD‐CN group (Figure 1). Further analyses revealed that there was an interaction effect for AP x Group on baseline delta responses [F(10,405)=11.629, p<0.001], and follow‐up delta [F(10,405)=9.569, p<0.001] responses. At baseline, PD‐MCI had reduced delta EROs in all electrode locations except occipital than both PD‐CN and HC, while PD‐CN had reduced delta responses than HC over frontal and central areas (for all; p<0.030) (Figure 2). At follow‐up, higher delta responses were detected in HC compared to both PD‐CN and PD‐MCI over all locations except occipital area (for all; p<0.001) (Figure3).ConclusionsThe current study revealed that longitudinal delta ERO reduction was apparent only in PD‐CN group. Individuals with PD‐MCI demonstrated decline at both baseline and follow‐up assessments. These findings may be interpreted as diminished delta EROs can be a successful indicator of subtle cognitive alterations in PD‐CN before neuropsychological assessments.