Fig. 3

EEG source signals in the hippocampus. Due to data quality issue, only a part of the participants was included in the EEG analysis (n = 34). (a) The changes of theta-gamma coupling from baseline to the end of the intervention were contrasted between the tACS group (n = 16) and the sham group (n = 18). The results are displayed for the left and right hippocampus within the range of theta phase (4–8 Hz) and gamma power (30–50 Hz). (b) A statistically significant correlation was observed between the change of theta-gamma coupling at 5.5–41.5 Hz and the change of MMSE (left, n = 34). There was also a statistically significant correlation between the theta-gamma coupling at 6.5–30 Hz and the delayed recall score in the tACS group (n = 16) at the end of intervention (right)

TGC, theta-gamma coupling