Effects of Transcranial Direct Current Stimulation on EEG Power and Brain Functional Network in Stroke Patients

Transcranial direct current stimulation (tDCS) has become a new method of rehabilitation treatment for stroke and is gradually gaining acceptance. However, the neurophysiological mechanisms of tDCS in the treatment of stroke still need to be further explored. In our research, we aimed to investigate the effects of tDCS on neural oscillation power and brain functional network (BFN) connectivity in stroke patients based on electroencephalogram (EEG). Fifteen patients with ischemic stroke attended two experimental sessions in a randomized crossover trial and received real and sham tDCS. Resting-state EEG signals were acquired before and after stimulation. First, the power of EEG delta, theta, alpha, beta, and gamma bands were analyzed before and after stimulation. Then, BFNs in different bands were constructed, and network characteristic parameters such as degree, clustering coefficient, characteristic path length, global efficiency, and small-world attribute were analyzed. The results showed that the delta power decreased significantly ( ${P}< {0.05}$ ) and the alpha power increased significantly ( ${P}< {0.05}$ ) after real tDCS, whereas the theta, beta, and gamma power did not change significantly ( ${P}>{0.05}$ ). The degree and global efficiency of the delta band BFN decreased significantly after real tDCS ( ${P}< {0.05}$ ), the characteristic path length increased significantly ( ${P}< {0.05}$ ), and the clustering coefficient and small-world attribute decreased but not statistically significant ( ${P}>{0.05}$ ). The degree, clustering coefficient, global efficiency, and small-world attribute of the alpha band BFN increased significantly after real tDCS ( ${P}< {0.05}$ ), and the characteristic path length decreased significantly ( ${P}< {0.05}$ ). The BFN characteristic parameters in theta, beta, and gamma bands did not change significantly after real tDCS ( ${P}>{0.05}$ ). There was no significant difference in sham tDCS group ( ${P}>{0.05}$ ). Our study found that the power of delta oscillations decreased and the global connectivity of delta band BFN weakened after tDCS in stroke patients, whereas the power of alpha oscillations increased and the global and local connectivity of alpha band BFN was enhanced. The findings implied that one of the neurophysiological mechanisms of tDCS treatment in stroke patients may be the modulation of the power of delta and alpha oscillations, as well as the improvement of the connectivity of delta and alpha oscillation networks.