Transcranial Alternating Current Stimulation at the Individual Alpha Frequency Shows Potential Value in Improving Working Memory in Healthy Participants

OBJECTIVE: To clarify the promoting effect of transcranial alternating current stimulation (tACS) at the individual alpha frequency (IAF) of the left posterior parietal cortex (PPC) on working memory (WM) using combined behavioral and electroencephalography (EEG) detection techniques. METHODS: This study is a single-blind, randomized, crossover, controlled trial with three groups: the IAF group, the IAF-1 group, and the sham group. WM was assessed using the n-back task, while EEG signals were simultaneously collected. Behavioral and EEG-related indicators pre and post stimulation were compared. RESULTS: Compared with pre-stimulation, the average reaction time (RT) in the n-back task significantly decreased (p < 0.001) and the d' value significantly increased (p < 001) in all participants post-stimulation. No significant local or whole-brain statistical differences in event-related desynchronization/synchronization(ERS/ERD) were found post-stimulation. However, event-related potential (ERP) analysis showed that the P200 amplitude (Fz: p = 0.023, F3: p = 0.017) and P300 amplitude (Fz: p = 0.009, Cz: p = 0.025) in the 3-back task of the IAF group significantly increased after stimulation. In the IAF group, a significant negative correlation was found between ΔP300 and ΔRT (Fz: r = -0.465, p = 0.039; Cz: r = -0.677, p = 0.001). No significant correlation was found between IAF amplitude and behavioral changes (ΔRT and Δd) or ERP changes (ΔP200 and ΔP300) (p > 0.05). No significant correlations were found in the IAF-1 group or the sham group (p > 0.05). CONCLUSION: IAF-tACS specially improved the high-load WM performance in healthy participants through increased P300 amplitude in the frontocentral region, which provides a brand-new strategy for precise regulation in the future. Further research are needed to confirm its clinical application.