Subjective perception of sleep is not necessarily consistent with electroencephalography (EEG) indications of sleep. The mismatch between subjective reports and objective measures is often referred to as "sleep state misperception." Previous studies evince that this mismatch is found in both patients with insomnia and in normal sleepers, but the neurophysiological mechanism remains unclear. The aim of the study is to explore the neurophysiological basis of this mechanism, from the perspective of both EEG power and functional magnetic resonance imaging (fMRI) fluctuations. Thirty-six healthy young adults participated in the study. Simultaneous EEG and fMRI recordings were conducted while the participants were trying to fall asleep in an MRI scanner at approximately 9:00 pm. They were awakened after achieving stable N1 or N2 sleep, or after 90 min without falling into stable sleep. Next they were asked to recall their conscious experiences from the moment immediately prior to awakening. Sixty-one instances of scheduled awakenings were collected: 21 of these after having achieved stable stage N2 sleep; 12, during stage N1 sleep; and, 20 during the waking state. Relative to those awakenings without subjective-objective discrepancy (n = 27), these awakenings with discrepancy (n = 14) were associated with lower θ power, as well as higher α, β, and γ power. Moreover, we found that participants who exhibited the discrepancy, compared with those who did not, evinced a higher amplitude of low-frequency fluctuation levels in the prefrontal cortex. These results lend support to the conjecture that the subjective-objective discrepancy is associated with central nervous system hyperarousal.
The function of sleep in humans has been investigated using simultaneous electroencephalography (EEG) and functional magnetic resonance imaging recordings to provide accurate sleep scores with spatial precision. Recent studies have demonstrated that spontaneous brain oscillations and functional connectivity dissociate during nonrapid eye movement (NREM) sleep; this leads to spontaneous cognitive processes, such as memory consolidation and emotional modulation. However, variations in network connectivity across the sleep stages or between sleep/wake transitions require further elucidation. We observed changes in the connectivity of the sensorimotor and default-mode networks (DMN) mediated by midnight sleep among 18 healthy participants. The results indicated that (1) functional connectivity in both networks showed increasing dissociation as NREM sleep deepened, whereas hyperconnectivity occurred during rapid eye movement (REM) sleep; and (2) compared with connectivity before sleep, the DMN presented a comparable connectivity pattern immediately after awakening, whereas the connectivity of the sensorimotor network remained disrupted. These findings showed that connectivity patterns dissociate and reconnect coherently in both cortical networks during NREM and REM sleep, respectively. After the person awakened, the DMN connectivity was re-established before the sensorimotor reconnection. These dynamic sleep-related dissociations and reconnections between sleep/wake conditions might provide the key to understanding cognitive modulations in sleep. If so, connectivity changes might serve as an alternative indicator beyond the EEG signature to unveil the spontaneous processes that occur during sleep.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.