Modulation effect of transcranial direct current stimulation on phase synchronization in motor imagery brain-computer interface

Transcranial direct current stimulation (tDCS) has been demonstrated that it can enhance the cortex excitability and modulate the event-related desynchronization (ERD) in motor imagery (MI). Phase synchronization is an important signature in the brain that reflects the neural interaction and integration, which has been adopted as an important EEG pattern for Brian-Computer Interface (BCI) control. In this study, we designed an experiment paradigm and investigated whether the tDCS can modulate the phase synchronization between the primary motor cortex (M1) and the supplementary motor area (SMA) in MI. Ten healthy subjects were selected and separated into two groups randomly. They performed the left and right hand MI task in two successive sessions. According to the different groups, anodal or sham stimulation were administrated to the right side of the M1. The phase locking value (PLV), which is a reliable measurement of phase synchronization in MI, was calculated. The pre and post-stimulation normalized PLV in the left hand MI task were compared. The result manifests that the normalized PLV of the entire subjects in anodal stimulation group increases after the stimulation, which shows a statistically significant difference (paired t-test p = 0.0371, n = 5). Our study reveals that the tDCS can impact the neural coupling between different brain regions and modulate phase synchronization in MI. Moreover, intervention of phase synchronization by tDCS might contribute to the rehabilitation of people with motor disorder and neurological disorders.