Fig. 1: Local wake slow waves (LoWS) recapitulate defining features of sleep slow waves.

a, b Properties of sleep slow waves (SWs). After a period of wakefulness, SWs present with increased rate, slope and amplitude, reflecting increased homeostatic sleep pressure. Neuronal activity (black vertical lines) aligns with the up-state of SWs. High-gamma (HG, 45–130 Hz) power, color-coded from blue (low) to red (high), reflects this increased neuronal activity. During the down-state, neurons are silent (low HG power). Synapses (purple) are pruned and neurons move from more (green) to less (gray) excitable. b After a period of sleep, the rate, slope and amplitude of SWs decrease, reflecting the decrease in homeostatic sleep pressure. c Example of identified negative and positive slow waves during wakefulness (nSW and pSW respectively, patient 3, electrode 1, 247 nSW and 207 pSW, mean in blue). nSW and pSW correspond to positive and negative extracellular polarity respectively, the former reflecting hyperpolarization of neurons, a core feature of sleep SW. d Grand average LoWS across participants (mean ± SD). e Normalized HG (45–130 Hz) power during the nSW-associated down-state (averaged between the two 0-crossings of nSW) shows a significant decrease relative to baseline (two-sided permutation paired t-test, p = 0.0004, n = 17 patients, ES: mean and 95% CI). Time-frequency decomposition of nSW (f) and pSW (g) converted into t-statistic values. Black line: grand average nSW and pSW. Note the drop in HG power at nSW trough. In contrast, the drop in HG power precedes pSW and corresponds to the peak of nSW occurrence before pSW. Panels g and i are temporally aligned. Mean ± SD (n = 17) co-occurrence of pSW and nSW (h) and the inverse (i), using true position (blue) and shuffled position (black, control) of nSW and pSW. nSW and pSW thus occur mainly as 3 peaks (1.5 oscillatory cycles). Note the alignment of the peak of nSW occurrence before pSW and the drop of HG power seen in g. Scale: per patient, per nSW and pSW, per unit of time (i.e., percentage of nSW and pSW that is preceded/followed by another wave). ES effect size.