# Correlation between brain symmetry index and motor function in Parkinson’s disease: a cross-sectional study

## TL;DR

This study finds that brain asymmetry measured by EEG correlates with motor function decline in Parkinson’s disease patients.

## Contribution

The study introduces a brain symmetry index (pdBSI) derived from EEG as a potential biomarker for hemispheric asymmetry in Parkinson’s disease.

## Key findings

- PD patients showed higher pdBSI levels in central and posterior brain regions compared to healthy individuals.
- β2-pdBSI in central and posterior regions correlated with gait impairment severity in advanced PD patients.
- Early PD patients exhibited the highest pdBSI levels, suggesting a stage-dependent shift in brain asymmetry.

## Abstract

Parkinson’s disease (PD) present with asymmetric motor impairments in the different stages. The study aims to explore the pair-wise derived brain symmetry index (pdBSI) of electroencephalography (EEG) for the stage in PD.

96 early Stage (ePD), 85 advanced Stage (aPD) and 67 healthy individuals were recruited. EEG and MDS-UPDRS Scale were applied to the study. pdBSI of EEG was calculated and divided into the frontal, the central and the posterior regions.

The PD Group exhibited significant differences in pdBSI across the full-frequency band in the whole-brain, especially in the central region. The PD groups showed higher levels of α-pdBSI, β1-pdBSI, and β2-pdBSI in the whole-brain than the healthy group. Furthermore, the ePD group showed higher levels of θ-pdBSI, α-pdBSI, β1-pdBSI and β2-pdBSI in the central region than the healthy group. The same tendency was observed between the aPD and healthy group. The β2-pdBSI of the posterior regions in ePD and aPD was higher than the healthy group. The results showed that ePD had the highest pdBSI level, followed by the aPD and healthy group. There was a positive correlation between β2-pdBSI of the central and posterior regions with the gait sub-score of the UPDRS-III in the aPD group.

There were hemispheric asymmetry in the PD patients. The pdBSI was a potential electrophysiological biomarker for hemispheric asymmetry in the PD. β2-pdBSI in the central and posterior region was significantly associated with the severity of gait impairment in aPD patients. In addition, the stage-dependent gradient elucidates the dynamic shift from unilateral to bilateral network involvement. Our findings underscore that quantifying interhemispheric asymmetry, beyond examining power in isolated regions, provides unique insights into the pathophysiology and clinical progression of PD.