The oscillatory features of non-REM sleep states have been a subject of intense research over many decades. However, a systematic spatial characterization of the spectral features of cortical activity in each sleep state is not available yet. Here, we used magnetoencephalography (MEG) and electroencephalography (EEG) recordings during night sleep. We performed source reconstruction based on the individual subject's anatomical magnetic resonance imaging (MRI) scans and spectral analysis on each non-REM sleep epoch in eight standard frequency bands, spanning the complete spectrum, and computed cortical source reconstructions of the spectral contrasts between each sleep state in comparison to the resting wakefulness. Despite not distinguishing periods of high and low activity within each sleep stage, our results provide new information about relative overall spectral changes in the non-REM sleep stages. Brain activity both during wakefulness and sleep is characterized by fluctuations in neuronal responses and rhythmic activation at various time scales. Sleep occurs periodically following a rather strict circadian rhythm and is itself a highly dynamic event, characterized by re-occurring and alternating phases of circa 80-120 minutes each, during which different polysomnographic events can be recorded 1. In each sleep stage, the brain is characterized by specific patterns of oscillatory activity. These oscillatory patterns of the sleeping brain have been described mostly using EEG. Our aim is to exploit the higher localization accuracy of magnetoencephalography (MEG) to shed new light on the spatial distribution of oscillatory features in non-REM sleep stages. The first light sleep stage (N1) is a state of drowsiness and of early loss of consciousness, physiologically characterized by a decreasing low voltage EEG frequency (2-7 Hz) 2. The following, second sleep stage (N2) is characterized by the occurrence of sleep spindles and K-complexes in the EEG signal. Spindles are rhythmic bursts of EEG activity that oscillate at a frequency between 12-15 Hz (classically named as sigma band). They have a waxing and a waning component and last for about 1 sec at a time 3,4. K-complexes are variable patterns of sudden bursts consisting mostly of a high voltage diphasic slow wave, especially in N2. Their brief negative peak in the EEG seems to be a signature of neuronal hyperpolarization, while its initial positive component depends on excitation of neurons. Often K-complexes co-occur with sleep spindles or may even trigger them 5. They are either spontaneous or occur in response to sudden sensory stimuli 6. As sleep deepens, subjects enter a third sleep stage, N3. This is characterized by a reduction of sleep spindles and by the emergence of low-frequency, high-amplitude fluctuations (delta waves) 7,8. In the past, some studies further distinguished between N3 and another N4 state, based on some arbitrary percentage of slow wave oscillations (e.g., >20% and >50%, respectively), but for the purpose of this study we consider them...

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Introduction Sleep deprivation (SD) impairs cognitive performance but its impact on metacognition – i.e. the ability to introspect about cognitive performance – is less clear. A few studies have assessed metacognitive accuracy after acute sleep deprivation in tasks of executive functions and found no impairments. However, whether SD has no influence on metacognition of other cognitive domains such as perception has not been investigated. In this study, we examined how metacognitive accuracy in perceptual decision tasks is affected by 32 hours of sustained wakefulness. Methods 14 participants (3 males, aged 20-32) repeated four visual psychophysical tasks (orientation discrimination, two-flicker fusion, vernier acuity and a novel face/house discrimination in noise) at regular intervals during 32 hours of sustained wakefulness and once after 8 hours recovery sleep. In each task, we concurrently measured quantitative indices of perceptual threshold, confidence rating and metacognitive accuracy (i.e. how well confidence ratings discriminate correct vs incorrect perceptual judgements). Results We observed a gradual increase of perceptual threshold in all tasks with increased time awake. Furthermore, metacognitive accuracy gradually decreased during sustained wakefulness in all tasks. Specifically, the decrease in metacognitive accuracy was driven by over-estimated confidence in trials when participants made incorrect perceptual judgements. After recovery sleep, perceptual thresholds were reset to baseline for all tasks, while metacognitive accuracy was reset to baseline for the orientation discrimination and two-flicker fusion tasks only. Conclusion We showed that sustained wakefulness up to 32 hours increasingly impairs metacognitive accuracy in perceptual decision tasks. These results are consistent across different perceptual tasks, but are in contrast to previous studies showing preserved metacognition of executive functions after SD. Overall, this suggests that the fundamental mechanisms of perceptual metacognition may be similarly affected by sleep deprivation, but that SD selectively impacts different domains of metacognition, such as perceptual metacognition and metacognition of executive functions. Support (if any) MB - Cardiff University PhD Funding CS - Wellcome Trust 209192/Z/17/Z

We examined the effect of sleep deprivation (SD) on human brain white matter（WM） using advanced fixel-based analysis. MRI data collected at four morning time points (7-8am, before and after SD, one night recovery and 3 days recovery). Compared to the session before SD, several WM tracts involving in sleep and wakefulness regulation, memory consolidation and emotion response showed varied fiber density (FD), fiber cross-section (FC) and the combined measure of FD and FC (termed FDC) at different time points. These findings demonstrated the heterogeneous sensitivity of WM tracts in response to SD and the microstructural homeostasis.