Drawing the twilight zone EurekAlert! Science News

What happens in the brain when our consciousness goes down during general anesthesia and normal sleep? Finnish scientists studied this question with modern experimental designs and functional brain imaging. They successfully distinguished the specific changes associated with consciousness from the broader overall effects, and found that the effects of anesthesia and sleep on brain activity were similar. These novel findings highlight a core brain network that is fundamental to human consciousness.

Explaining the biological basis of human consciousness is one of the greatest challenges in science. Although loss and return of consciousness, as controlled by drugs or physical sleep, have been used as model systems in the study of human consciousness, previous research findings have been confused with much experimental simplification.

“One key challenge is to design an establishment, where brain data in different states are only different in terms of consciousness. Our study overcomes many former opponents. before, and for the first time, it reveals the cloud devices that underlie connected consciousness, ”said Harry Scheinin, Docent of Pharmacology, Anesthesiologist, and Principal Investigator of the study from the University of Turku, Finland.

New and innovative experimental setup

Brain activity was measured by positron emission tomography (PET) images during different states of consciousness in two separate experiments in the same group of healthy subjects. Measurements were made during arousal, elevation and sustained levels of two anesthetic agents, and during sleep-wake and non-rapid eye movement (NREM) movements.

In the first trial, the subjects were randomly assigned to receive either propofol or dexmedetomidine (two anesthetic agents with different molecular modes of action) at step elevations so that the subjects no longer responded. In the sleep study, they were allowed to fall asleep naturally. In both trials, the subjects were presented with a quick recovery to a responsive state, followed by immediate and in-depth interviews of personal experiences from the previous non-response period. Non-responsive anesthetic states and confirmed NREM sleep levels, where a subsequent report of psychiatric content showed no signs of consciousness in the surrounding world, revealed an unconnected state in study participants. Importantly, the drug dose in the first trial was not changed before or during the transition in the behavioral state of the subjects.

“This unique experimental design was the main idea of ​​our study and allowed us to differentiate the changes specific to the state of consciousness from the overall effects of anesthesia,” explains Annalotta Scheinin, Anesthesiologist, Advocate Doctoral and first author of the paper.

Researchers found a common basic brain network

When PET images of responsive and unrelated brains were compared with non-responsive and unrelated images, the scientists found that the activity of the thalamus, cingulate cortes and square gyri was independently affected by the anesthetic agent used, drug concentration and management of change in state of consciousness (see figure). Similar surprising results were obtained when physiological sleep was compared to sleep vigilance. Changes in brain activity were much more pronounced when the unrelated states were compared to a fully awake state. State-specific findings were thus differentiated and separated from the total effects of drug-induced anesthesia and natural sleep, which included widespread inhibition of brain activity across cortical areas.

These findings identify a key brain network that is fundamental to human consciousness.

“General anesthesia appears to be similar to normal sleep more than was traditionally thought. This explanation, however, is very consistent with our recent electrophysiologic findings in another anesthesia study,” he said. Harry Scheinin.

Topical experiences are common during general anesthesia

Interestingly, unconsciousness rarely marked unconsciousness (i.e., complete absence of personal experiences), as most participants reported created experiences within, such as dreams, in the interviews. This is not a completely new discovery because dreams are usually reported by patients after general anesthesia.

“However, because of the minimal delay between waking and interviews, the current results contribute significantly to our understanding of the nature of the anesthetic state. Contrary to popular belief, full consciousness is not required for general anesthesia. successful, as it is enough to just disconnect the patient ‘s experiences from what is going on in the operating room, “Annalotta Scheinin explained.

The new study sheds light on the fundamental nature of human consciousness and provides new information on brain functions in intermediate states between awakening and full consciousness. These findings can also challenge our current understanding of the meaning of general anesthesia.

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The experiments were carried out at the Turku PET Center as a joint effort between the research groups of Harry Scheinin studying the mechanisms of anesthesia, and Antti Revonsuo Professor of Psychology examining human consciousness and the brain from a philosophical and psychological perspective, in the collaboration with Professor Michael Alkire of the University of California, Irvine, USA. The Turku PET Center is a Finnish National Research Institute established by the University of Turku, Åbo Akademi University and Turku University Hospital. The study was funded by the Finnish Academy and the Jane and Aatos Erkko Foundation.