Fig. 4.

Evoked activity to repeated noise snippets during sleep. a Target-locked memory-evoked potentials (MEPs) in NREM2 (left), NREM3 (middle), and REM (right) stages of sleep for RefRN (orange) or RN (blue) trials compared to N trials. Central electrodes were used (circles on scalp topographies) and all targets but the first one from a given trial were used (9 targets per trial). Note the resemblance between the NREM2 MEPs and the MEPs observed in wakefulness (Fig. 2b). Horizontal bars show significant clusters (NREM2: ([305, 405] ms; NREM3: ([130, 300] ms; REM: [280, 390] ms; P _cluster < 0.05) for the RefRN vs. N difference (orange; no RN vs. N difference). Dotted lines denote the standard error of the mean across participants (N = 20). Insets: scalp distribution of t-values (RefRN vs. N, paired t-tests) over temporal windows corresponding to the abovementioned clusters. The gray contour shows the scalp distribution of the MEPs observed in wakefulness (Fig. 2b). MEPs were temporally smoothed using a 50 ms-wide Gaussian kernel. b Inter-trial phase coherency (ITPC) extracted over the entire night recordings (N = 20) on windows of 20 consecutive RefRN (orange bars) or RN (blue bars) trials. The corresponding windows were aggregated across participants (NREM2: N = 3698 and 3683; NREM3: N = 2480 and 2478; REM: N = 1190 and 1218 for RefRN and RN trials, respectively). ITPC was extracted around 2 Hz ([1.5, 3.5] Hz) and during stimulus presentation ([0.8, 5.5]s). Mixed-effects models revealed a significant interaction between sleep stages and stimulus condition (see Methods for details). Stars atop boxes indicate the results of post hoc statistical tests (t-tests against 0, P < 0.001: ***; P < 0.01: **; P < 0.05: *, NS: P ≥ 0.05). Note the significant increase in ITPC for RefRN compared to RN trials in stages NREM2 and REM but not in NREM3