Assessment of Changes in Brain Waves of Patients with Depression Under the Treatment of Transcranial Direct Current Stimulation (tDCS) Using Event Related Potential (ERP)

The main goal of this study is to present a proper index to assess the changes in brain activities of patients with severe depression by applying Transcranial Direct Current Stimulation (tDCS), using Event Related Potentials (ERPs).
Seven patients with severe depression (four males, with mean age 34.85±4.25), participated in this study. First, the participants were asked to fill out Hamilton’s anxiety and Beck’s depression questionnaires. Simultaneous to recording their brain signals, subjects were asked to participate in Stroop test. This test entails 360 stimulations which include 120 congruent, 120 incongruent, and 120 neutral stimulations lasting for 12 minutes. After recording the brainwaves, the Dorso Lateral Prefrontal Cortex (DLPFC) in patients’ left hemisphere is stimulated using tDCS, with 1mA current for 20 minutes, each session.
To analyze the data, ERP components were extracted using synchronous averaging. Then, five features proportional to Wavelet coefficients of each frequency band in every stimulation types were extracted from ERP components. Correlation between percentages of changes and the subjects’ Stroop test results were calculated before and after applying tDCS and the stimulation period. The results showed that the latency period of N400 component after applying tDCS was decreased significantly. Furthermore, a significant correlation was observed between congruent and incongruent stimulations and the increase in the Wavelet coefficients of alpha band in Pz channel with p=0.0128, r=0.9060 and p=0.0037, r=0.95 respectively.
Consequently, the alpha band power spectrum of parietal lobe will be significant correlation with the depression level by applying tDCS.