Role of EMG Rectification for Corticomuscular and Intermuscular Coherence Estimation of Spinocerebellar Ataxia Type 2 (SCA2)

Abstract

Corticomuscular and intermuscular coherence are established methods to study connectivity between activity of neurons in sensorimotor cortex measured with electroencephalography (EEG) and muscle measured with electromyography (EMG), or between muscles, in a variety of neurological conditions. However, there is a debate on the importance of EMG signal rectification before coherence estimation. This paper studies the effects of EMG rectification in corticomuscular and intermuscular coherence estimation from SCA2 patients and prodromal SCA2 gene mutation carriers in comparison to healthy controls. EEG and EMG were recorded from 20 SCA2 patients, 16 prodromal SCA2 gene mutation carriers and 26 healthy control subjects during a motor task in upper or lower limbs. Coherence estimations were carried out using the non-rectified raw EMG signal vs. the rectified EMG signal. The results showed that EMG rectification impairs the level of significance of the differences in corticomuscular and intermuscular coherence between SCA2 patients and prodromal SCA2 gene mutation carriers vs. healthy controls in the beta-band, and also results in overall lower coherence values.