Figure 1
Comparison of early and late responses between up- and down-PTAS. (A) Averaged EEG across stimuli (left y-axis) following actual (solid line) and SHAM stimulation (dotted line) in a night with up- (top) and down-PTAS (bottom). EEG data time-locked to the initial stimulus (0 s) of a given stimulation window (ON window) of channel Fz is displayed. The background illustrates the event-related spectral perturbation (ERSP; right y-axis) comparison with SHAM (paired t test). Arrows below the time axis signify time periods utilized for statistical comparisons in (C). The illustrated averaged waveforms and ERSP were computed using data from all windows regardless of the number of stimuli. (B) Displayed is the auditory evoked response (AER, mean ± 95% CI), obtained by, for a given participant, subtracting the mean waveform following SHAM (representing the mean targeted slow wave), from the mean waveform during STIM (reflecting a combined response of the mean targeted slow wave and the AER itself). The AER was first computed for each participant individually and then averaged across all participants. The lines depict the average over participants. The P200, N550 and P900 are indicated with arrows. The illustrated AER was computed using data from all windows regardless of the number of stimuli. Of note, no considerable difference in the shape or amplitude of the AER was observed when considering windows with few or many stimuli only. (C) Mean slow-wave activity (1–4 Hz; left) and sigma activity (12–16 Hz; right) averaged over all channels. Asterisks above box plots indicate statistically significant differences between STIM and SHAM (paired t test, * p < .05, ** p < 0.01, n.s. p \(\ge\) 0.05). The early slow-wave (0.25–1.75 s) and sigma response (0.75–1.25 s) suggest a K-Complex-like response following both up- and down-PTAS. The later slow-wave response (4–6 s) is significantly stronger after up-PTAS compared to down-PTAS (as indicated by the horizontal bar).
