Variability in how people perceive the same sensory stimulus from one moment to the next may stem from ongoing fluctuations in baseline brain activity. This review examines evidence that activity levels in sensory brain areas before a stimulus predict whether that stimulus will be consciously perceived. The findings are discussed in the context of recent discoveries about the structure of spontaneous BOLD signal fluctuations in the awake human brain, and possible sources of these baseline fluctuations are considered.
Lucid dreaming occurs when a person realizes they are dreaming while still asleep, often involving vivid images and unusual bodily sensations like flying. A new multicomponent framework proposes that lucid dreaming arises from prediction error signals during sleep, which are resolved by creating a superordinate self-model that integrates ambiguous sensory inputs from both the body and higher brain regions. Multisensory integration maintains lucidity and contributes to kinesthetic experiences, while attentional control balances top-down mental models and bottom-up sensory precision. This framework links neural correlates of lucid dreaming to sleep and arousal regulation, generating testable predictions about individual differences and neurocognitive mechanisms that induce lucid dreams.
Mind-wandering, where attention shifts from the present to internal thoughts, is more likely after nights with less REM and N2 sleep and less intense dream experiences. Over 7 nights, 67 healthy participants wore mobile sleep EEG headbands and completed self-reports, yielding about 400 analyzable nights. Nights with more wakefulness and shorter REM and slow wave sleep were linked to poorer subjective sleep quality. Reduced REM and N2 sleep, along with less vivid dreams, predicted increased mind-wandering the following day. The findings highlight that night-to-day variations in specific sleep stages influence both perceived sleep quality and daytime mind-wandering intensity.
Dreaming and the forgetting of dreams are not meaningless byproducts of sleep but are integral to the brain's homeostatic functions, which both restore and anticipate future needs. Mental activity during sleep, especially in the second half of the night, is a self-focused, future-oriented cognitive process. Waking up shifts the brain to a constrained, goal-directed mode of thinking that competes for neural resources with dream production and recall, contributing to dream amnesia. Cortisol is highlighted as a potential factor in predictive homeostasis and forgetting dreams. This theoretical proposal reframes dreaming as part of a reactive and predictive homeostatic system.