Foundations of human consciousness: Imaging the twilight zone

Annalotta Scheinin, Oskari Kantonen, Michael Alkire, Jaakko Långsjö, Roosa E. Kallionpää, Kaike Kaisti, Linda Radek, Jarkko Johansson, Nils Sandman, Mikko Nyman, Mika Scheinin, Tero Vahlberg, Antti Revonsuo, Katja Valli, Harry Scheinin

Research output: Contribution to journalArticleScientificpeer-review

2 Citations (Scopus)
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What happens in the brain when conscious awareness of the surrounding world fades? We manipulated consciousness in two experiments in a group of healthy males and measured brain activity with positron emission tomography. Measurements were made during wakefulness, escalating and constant levels of two anesthetic agents (experiment 1, n=39), and during sleep-deprived wakefulness and non-rapid eye movement sleep (experiment 2, n=37). In experiment 1, the subjects were randomized to receive either propofol or dexmedetomidine until unresponsiveness. In both experiments, forced awakenings were applied to achieve rapid recovery from an unresponsive to a responsive state, followed by immediate and detailed interviews of subjective experiences during the preceding unresponsive condition. Unresponsiveness rarely denoted unconsciousness, as the majority of the subjects had internally generated experiences. Unresponsive anesthetic states and verified sleep stages, where a subsequent report of mental content included no signs of awareness of the surrounding world, indicated a disconnected state. Functional brain imaging comparing responsive and connected versus unresponsive and disconnected states of consciousness during constant anesthetic exposure revealed that activity of the thalamus, cingulate cortices, and angular gyri are fundamental for human consciousness. These brain structures were affected independent from the pharmacologic agent, drug concentration, and direction of change in the state of consciousness. Analogous findings were obtained when consciousness was regulated by physiological sleep. State-specific findings were distinct and separable from the overall effects of the interventions, which included widespread depression of brain activity across cortical areas. These findings identify a central core brain network critical for human consciousness.

Original languageEnglish
Pages (from-to)1769-1778
Number of pages10
JournalJournal of Neuroscience
Issue number8
Publication statusPublished - 24 Feb 2021
Publication typeA1 Journal article-refereed


  • Anesthesia mechanisms
  • Consciousness
  • Dexmedetomidine
  • Positron emission tomography
  • Propofol
  • Sleep

Publication forum classification

  • Publication forum level 3

ASJC Scopus subject areas

  • Neuroscience(all)


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