Blind Source Separation of Transcranial Direct Current Stimulation from Simultaneous Electroencephalograph Measurement

Brain stimulation is a novel physical therapy promising for treating mental disorders that are not impacted by medication and psychotherapies. Recently, most studies can only investigate the brain state before and after the stimulation period, especially transcranial electrical stimulation (tES). Due to the tES interference, it is a challenging task to investigate the brain state through electroencephalography (EEG) during the stimulation period. This study proposed a blind source separation algorithm to remove the transcranial direct current stimulation (tDCS) from the simultaneous EEG recording and reconstruct the EEG signals. Ten participants were recruited in this study, which needed to apply 5 min tDCS with 1mA intensity. Before and after tDCS stimulation, 2 min resting state was also recorded for comparison purposes. The results indicated that the proposed method, independent component analysis, can be used to reconstruct EEG signals from the interfered mixed signals. Additionally, 5 min tDCS could induce neurophysiology alternation of brain oscillation (i.e., theta and alpha band) and intra-hemisphere connectivity. Conclusively, the proposed method provides a way to assess the brain state and the underlying mechanism of the tDCS in the pre, during, and post period. It will help guide the researcher or clinical doctor to visualize the brain activation during the stimulation and adjust their stimulation protocol to achieve optimal stimulation performance.