Evoked Alpha Power is Reduced in Disconnected Consciousness During Sleep and Anesthesia

Matthieu Darracq,Olivia Gosseries,Jean-Francois Brichant,Daniel Polyakov,Jaakko O Nieminen,Vincent Bonhomme,Steven Laureys,Robert D Sanders,Chadd M Funk,Giulio Tononi,Brady Riedner,Melanie Boly

doi:10.1038/s41598-018-34957-9

Abstract

Sleep and anesthesia entail alterations in conscious experience. Conscious experience may be absent (unconsciousness) or take the form of dreaming, a state in which sensory stimuli are not incorporated into conscious experience (disconnected consciousness). Recent work has identified features of cortical activity that distinguish conscious from unconscious states; however, less is known about how cortical activity differs between disconnected states and normal wakefulness. We employed transcranial magnetic stimulation–electroencephalography (TMS–EEG) over parietal regions across states of anesthesia and sleep to assess whether evoked oscillatory activity differed in disconnected states. We hypothesized that alpha activity, which may regulate perception of sensory stimuli, is altered in the disconnected states of rapid eye movement (REM) sleep and ketamine anesthesia. Compared to wakefulness, evoked alpha power (8–12 Hz) was decreased during disconnected consciousness. In contrast, in unconscious states of propofol anesthesia and non-REM (NREM) sleep, evoked low-gamma power (30–40 Hz) was decreased compared to wakefulness or states of disconnected consciousness. These findings were confirmed in subjects in which dream reports were obtained following serial awakenings from NREM sleep. By examining signatures of evoked cortical activity across conscious states, we identified novel evidence that suppression of evoked alpha activity may represent a promising marker of sensory disconnection.

Highlights

Conscious experience is reversibly altered by sleep and anesthesia
To assess whether alpha-band responses were reduced in disconnected conscious states following transcranial magnetic stimulation (TMS), we performed time–frequency analysis on EEG data recorded over posterior cortex of data collected in wake compared to rapid eye movement (REM) sleep (n = 7) or ketamine anesthesia (n = 6)
When restricted to the alpha band from 8–14 Hz, we found significant differences between 8–11 Hz for ketamine anesthesia and 10–12 Hz REM sleep

Summary

Introduction

During deep non-rapid eye movement (NREM) sleep or following administration of anesthetics such as propofol, consciousness may be transiently abolished In other states, such as rapid eye movement (REM) sleep and ketamine anesthesia, conscious experience occurs but most external stimuli are not incorporated into what the subject is experiencing. In conscious states including wake, REM sleep, and ketamine anesthesia, cortical responses exhibit rich spatiotemporal responses that persist in time and space, reflecting a capacity for entering a large repertoire of cortical states that is likely a prerequisite for consciousness[4,5] These and other studies have established common features of conscious states, but the question of how cortical function differs between disconnected and connected states remains. We hypothesized that evoked alpha power could be a marker of sensory disconnection

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Conclusion