The Increase of Theta Power and Decrease of Alpha/Theta Ratio as a Manifestation of Cognitive Impairment in Parkinson's Disease

Abstract

In this study, we aim to assess and examine cognitive functions in Parkinson's Disease patients using EEG recordings, with a central focus on characteristics associated with a cognitive decline. Based on neuropsychological evaluation using Mini-Mental State Examination, Montreal Cognitive Assessment, and Addenbrooke's Cognitive Examination-III, 98 participants were divided into three cognitive groups. All the particpants of the study underwent EEG recordings with spectral analysis. The results revealed an increase in the absolute theta power in patients with Parkinson's disease dementia (PD-D) compared to cognitively normal status (PD-CogN, p=0.00997) and a decrease in global relative beta power in PD-D compared to PD-CogN (p=0.0413). An increase in theta relative power in the left temporal region (p=0.0262), left occipital region (p=0.0109), and right occipital region (p=0.0221) were observed in PD-D compared to PD-N. The global alpha/theta ratio and global power spectral ratio significantly decreased in PD-D compared to PD-N (p = 0.001). In conclusion, the increase in relative theta power and the decrease in relative beta power are characteristic changes in EEG recordings in PD patients with cognitive impairment. Identifying these changes can be a useful biomarker and a complementary tool in the neuropsychological diagnosis of cognitive impairment in Parkinson's Disease.

Keywords: Parkinson’s disease; dementia; mild cognitive impairment; quantitative EEG; spectral analysis.

Figure 1

Flow chart of patients selection.

Figure 2

Relative beta power in the different areas between patient’s groups with statistical significance highlighted (* $p<0.05$, ** $p<0.01$).

Figure 3

Relative theta power in the different areas between patient’s groups with statistical significance highlighted (* $p<0.05$).

Figure 4

Alpha/theta ratio in the different areas between patient’s groups with statistical significance highlighted (* $p<0.05$, ** $p<0.01$, *** $p<0.001$).

Figure 5

Spectral PowerRatio in the different areas between patient’s groups with statistical significance highlighted (* $p<0.05$, ** $p<0.01$).

Figure 6

Average topographic maps of Alpha/Theta ratio in patient’s groups.

Figure 7

Average topographic maps of SPR in groups.

Figure 8

Linear regression of global alpha/theta ratio (a) and global SPR (b) versus PD duration in PD-MCI group.

Figure 9

Linear regression of absolute global low alpha (a) and absolute global theta (b) versus age in PD-CogN group.

Figure 10

Distributions of theta PLI between selected regions which are significantly different between patient’s groups (* $p<0.05$, ** $p<0.01$).