Full anesthesia does not completely shut off a person's consciousness - he continues to react to events in the world around him, although he does not realize this, doctors say in an article published in the journal Anesthesiology.
“It seems that anesthesia is more like a normal sleep than a complete blackout. As in deep sleep, our brain can “see” dreams, perceive information and recognize external stimuli at the subconscious level,”says Antti Revonsuo from the University of Turku (Finland).
Since the advent of the first anesthetic drugs that plunge people into unconsciousness and prevent them from feeling pain, scientists have been debating exactly how they work. Some doctors believe that they simply immerse patients in a state of deep sleep, which, in principle, does not differ from its natural counterpart.
Other doctors disagree with this interpretation, referring to experiments and observations of recent years, indicating that general anesthesia stops a person's internal bioclock and increases the chances of developing dementia and Alzheimer's disease in elderly patients. All this, they believe, suggests that such drugs immerse a person in a completely different state, which has no analogues in nature.
Revonsu and his colleagues proved that the proponents of the first idea are closer to the truth by conducting a highly unusual experiment among students at their university. Having recruited fifty volunteers, the scientists invited them to take large doses of two anesthetics - dexmedetomidine and propofol, used today in surgical operations.
When all the participants in the experiment “turned off,” the doctors began to observe with the help of an electroencephalograph whether the work of their brain was changing at the moment when various pleasant and unpleasant sounds began to be heard from nearby speakers, including meaningful phrases in Finnish.
Some of the sounding proposals were changed in such a way that they became absurd. For example, the announcer solemnly declared that "the night sky was filled with shiny tomatoes." By observing the reaction of the brain of their wards to such phrases during anesthesia and after awakening, scientists tried to understand how much he was disconnected from the perception of reality.
As it turned out, the anesthesia deprived the participants of the experiment of the ability to distinguish between reality and absurdity - they reacted to different sentences in the same way. On the other hand, the very fact that they recognized the sounds of speech, although they did not remember later what the speaker said, indicates that the drugs do not turn off consciousness one hundred percent.
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This is evidenced by the students' encephalograms themselves - waves appeared on them, characteristic of episodes of deep sleep, when a person continues to perceive reality, but cannot move his arms and legs and is not aware of it. This is also supported by the fact that when relatively small doses of dexmedetomidine and propofol were administered, students could be awakened by touching them or speaking loudly in their immediate vicinity.
If anesthesia really plunges a person into deep sleep, then, as Revonsu notes, it can be used to study the nature of consciousness and its individual components. In addition, it will facilitate the design and validation of new anesthetics that have fewer dangerous side effects compared to dexmedetomidine and propofol.