Assessing sleep consciousness within subjects using a serial awakening paradigm

Abstract

Dreaming—a particular form of consciousness that occurs during sleep—undergoes major changes in the course of the night. We aimed to outline state-dependent features of consciousness using a paradigm with multiple serial awakenings/questionings that allowed for within as well as between subject comparisons. Seven healthy participants who spent 44 experimental study nights in the laboratory were awakened by a computerized sound at 15–30 min intervals, regardless of sleep stage, and questioned for the presence or absence of sleep consciousness. Recall without content (“I was experiencing something but do not remember what”) was considered separately. Subjects had to indicate the content of the most recent conscious experience prior to the alarm sound and to estimate its duration and richness. We also assessed the degree of thinking and perceiving, self- and environment-relatedness and reflective consciousness of the experiences. Of the 778 questionings, 5% were performed during wakefulness, 2% in stage N1, 42% in N2, 33% in N3, and 17% in rapid eye movement (REM) sleep. Recall with content was reported in 34% of non-REM and in 77% of REM sleep awakenings. Sleep fragmentation inherent to the study design appeared to only minimally affect the recall of conscious experiences. Each stage displayed a unique combination of characteristic features of sleep consciousness. In conclusion, our serial awakening paradigm allowed us to collect a large and representative sample of conscious experiences across states of being. It represents a time-efficient method for the study of sleep consciousness that may prove particularly advantageous when combined with techniques such as functional MRI and high-density EEG.

Stratification of unresponsive patients by an independently validated index of brain complexity

“…Here we consider PCI, a measure that gauges the ability of thalamocortical circuits to integrate information irrespectively of the integrity of sensory processing, motor behavior, and subject participation. To validate PCI, we chose benchmark conditions15 in which subjects could provide a report about the absence or presence of conscious experience, including delayed reports upon awakening from sleep27 and anesthesia 9. Retrospective reports, either immediate or delayed, are the current gold standard for assessing the presence and content of subjective experience16 and therefore for validating objective measures of consciousness 9.…”

Activation of the motor cortex during phasic rapid eye movement sleep

“…Dreams are frequently reported by subjects awakened from rapid eye movement (REM) sleep 1, 2. In our dreams, we can move and perform various complex motor behaviors while being completely motionless due to an atonia of postural muscles 3.…”

Occipital long-interval paired pulse TMS leads to slow wave components in NREM sleep

“…However, although phenomenal content clearly exists in the NREM state (e.g. Noreika et al, 2009;Siclari et al, 2013) NREM state is definitely a state closer to unconsciousness than consciousness. Indeed, in roughly 30% of the awakenings from NREM sleep subjects report having no conscious experience (Noreika et al, 2009;Siclari et al, 2013).…”

“…Noreika et al, 2009;Siclari et al, 2013) NREM state is definitely a state closer to unconsciousness than consciousness. Indeed, in roughly 30% of the awakenings from NREM sleep subjects report having no conscious experience (Noreika et al, 2009;Siclari et al, 2013). Moreover, indisputably the fullness, steadiness and richness of contents in a conscious state considerably exceeds the hypothetical conscious contents retrospectively assessed for NREM sleep.…”

“…Our working assumption is that although NREM sleep cannot be considered a completely unconscious state (e.g. Noreika, Valli, Lahtela, & Revonsuo, 2009;Siclari, LaRocque, Postle, & Tononi, 2013), the contrast between NREM sleep and wakefulness nevertheless is a good proxy for the comparison of unconscious and conscious states. In other words, NREM sleep is a state close to unconsciousness (e.g.…”