Feeling deeply asleep may not align with actual sleep stages. In a study involving 30 participants (20 good sleepers and 10 with sleep misperception), 787 awakenings revealed that good sleepers often perceived their sleep as lightest during the first two hours of NREM sleep, typically seen as the deepest phase. In contrast, those with sleep misperception frequently felt awake and reported lighter REM sleep. High-density EEG data showed that widespread high-frequency power was inversely related to subjective sleep depth, challenging traditional views on deep sleep perception.
Incomplete awakenings from non-rapid eye movement sleep can produce sleepwalking and related behaviors, which sometimes involve conscious experience and later recall. Using high-density EEG and immediate interviews, the authors found that conscious experiences during these episodes (56% of cases) were preceded by high-amplitude slow waves in anterior brain regions and activation in posterior regions, patterns similar to those seen in dreaming. Recall of the experience (56% of cases) was linked to higher EEG activation in the right medial temporal area before movement. No conscious experience occurred in 19% of episodes, and no recall in 25%. These findings suggest that the brain activity underlying parasomnia experiences resembles that of dreams, pointing to core processes for sleep consciousness.
Conscious experience includes not only awareness of external objects but also a sense of the embodied self, which relies on integrating multisensory stimuli near the body, a process involving the Peripersonal Space (PPS) system. Using high-density EEG in awake participants, a neural marker of PPS—high-beta oscillations in centroparietal regions during audiotactile integration near versus far from the body—was identified. This marker persisted during dreaming and waking conscious states but was absent during dreamless, unconscious states. In patients with disorders of consciousness, the same index predicted behavioral measures of consciousness and clinical outcome, suggesting that multisensory integration within PPS is tightly linked to conscious experience.
A neural marker based on high-beta oscillations measured during a simple audiotactile task can detect consciousness and predict recovery in patients with disorders of consciousness. The marker, derived from the peripersonal space system, was present in healthy participants during wakefulness and dreaming but absent in dreamless sleep. In 72 patients with disorders of consciousness, the marker correlated with behavioral measures of consciousness and predicted recovery at discharge. The marker was also associated with forebrain mesocircuit integrity, suggesting a bedside-compatible tool for detecting covert consciousness and guiding clinical decisions in unresponsive patients.