Figure 5.
Local modulations of sleep rhythms in association to stimuli. a, Time-frequency decomposition of the EEG signal recorded at Cz in response to stimuli. The time-frequency decomposition was extracted for each trial in NREM sleep (light and deep) and averaged across participants (N = 18) (see Materials and Methods). Right after stimulus onset, a large increase in the low-frequency range (<6 Hz) and spindle range ([11, 16] Hz) can be observed, which correspond to slow waves and spindles evoked by stimuli. Interestingly, these sleep rhythms were suppressed later on, at the time during which a LRP was observed in light NREM sleep (Fig. 2). This decrease was confirmed in b by examining the modulation of the power (at Cz) in these 2 frequency bands (<6 Hz: slow-wave range, black curve; [11, 16] Hz: spindle range, gray curve). Horizontal bars represent the significant clusters determined across participants (pcluster < 0.05). Shaded areas represent the SEM computed across participants. Insets, Scalp topographies of the power within the slow-wave and spindle ranges at trial onset ([0, 2] s) and during the LRP window ([2.9, 3.8] s). Power was z-scored across sensors to emphasize regional differences. The decrease associated with the LRP is centrally distributed for slow waves and sleep spindles despite their originally frontal distribution, suggesting a local suppression of sleep rhythms. c, d, Same as a, b, except for REM sleep. Note the initial broadband increase in the higher frequency range (>12 Hz) and the decrease within the theta range ([4, 8] Hz). Scalp topographies were computed by averaging power over the significant clusters (pcluster < 0.05).