Offline, EEG data recorded immediately after HD-tACS administration were re-referenced to the average of the left and right mastoids, high-pass filtered at 0.1 Hz, and low-pass filtered at 170 Hz. Segments were cut −2000 to 5000 ms with respect to target onset. Using large segments allowed us to avoid edge artifacts caused by wavelet convolution during the memory maintenance period (i.e., 500 to 3000 ms post-target onset). Of note, although the comparison of data between memory and control blocks (described below under Statistics) allowed us to better isolate working memory related neural activity and reduce the influence of evoked activity and stimulus-driven processes, we nonetheless confirmed the statistical significance of all primary EEG results using the more conservative analytic window of 1000 to 3000 ms post-target onset. Visual inspection was initially used to remove large muscle artifacts, followed by an independent component analysis 71 to remove blink and noise artifacts 72. This resulted in an average 13.8 ± 5.8 components rejected.
