The EEG Correlates of Sleep Misperception

Introduction Sleep misperception (SMP), the impression of being awake despite polysomnographically documented sleep, is sometimes observed in healthy individuals and to an extreme degree in patients with paradoxical insomnia. The mechanisms underlying the subjective perception of sleep are not well understood. Here we asked whether high-density (hd) EEG, a technique with a refined spatial resolution, could identify local wake-like brain activity related to SMP. Methods 14 healthy subjects (age 33.6 ± 8.5 yrs, 10 females) underwent a serial awakening paradigm in the sleep lab while recorded with hdEEG (256 electrodes). 969 awakenings were performed across all sleep stages. At each awakening, subjects were asked to describe what was going through their mind and to estimate if immediately prior to the awakening they had been asleep or awake. Results SMP occurred in 10 subjects (15.92 ± 8.76% per subject, total of n=99 episodes of SMP). 70.83% of SMP episodes occurred in N1, 18.77% in N3, 9.79% in N2 and 3.57% in REM sleep. Only SMP in stages N2 and N3 was further considered. Compared to correct sleep perception (CSP), SMP occurred earlier in the night (147 ± 79 min after lights off vs 231 ± 25 min; p=0.0038). The presence of conscious experiences during sleep did not distinguish SMP from CSP, but experiences associated with SMP tended to be more thought-like and less perceptual compared to CSP (Score: 0.52 ± 1.17 for SMP; -1.00 ± 1.84 for CSP; p=0.076). SMP was associated with increased alpha (8−12 Hz) and sigma power (12−16 Hz) in central and posterior brain regions in the 20s before the awakening. No significant differences were observed for other frequency bands. Conclusion The preferential occurrence of SMP early in the night, its quasi-absence in REM sleep and its association with increased alpha power in sensorimotor regions may indicate that the subjective perception of sleep depends on the degree of sleep-related environmental disconnection. Further analyses are needed to determine whether these findings also apply to patients with paradoxical insomnia. Support (If Any) Swiss National Science Foundation, Divesa Foundation, Fondation Pierre Mercier pour la Science, Bourse pro-femmes de l’Université de Lausanne.