Researchers have conducted that general anesthesia may not be as general as we might think. In fact, the research suggests that parts of our consciousness stay "awake" during the procedure. Consciousness fully lost during anesthesia. The answer may surprise anesthesiologists and patients alike. Consciousness appears to be more persistent than we think. The study was published in the journal Anesthesiology.

Studying the brain under anesthesia

They randomly assigned 47 healthy volunteers to receive either propofol or dexmedetomidine. The drugs were administered gradually until the participants were no longer responsive, achieving a "presumable loss of consciousness."

At one point during this gradual process, "an attempt was made to arouse the participant to regain responsiveness while keeping the drug infusion constant." During the anesthesia, all of the participants were played "congruent and incongruent" sentences.

Congruent sentences ended as expected, whereas incongruent ones did not. Normally, during wakefulness, an EEG registers a spike in brain activity when a person hears an incongruent ending to a sentence. But, the researchers discovered that something interesting takes place in the brain when under general anesthesia.

The brain processes sound under anesthesia

When they used dexmedetomidine, they also the expected words created a significant response, meaning that the brain was trying to interpret the meaning of the words. However, after the participants woke from the anesthesia, they did not remember the sentences they had heard and the results were the same with both drugs.


Additionally, the researchers tested whether or not the participants' brains processed sounds that were not words. The volunteers were all played a range of unpleasant sounds while under, and they were playing the same sounds again after they had regained consciousness.

EEG results showed that their brains reacted more quickly to the unpleasant sounds that they'd been played while under anesthesia than to new sounds that they'd never heard, suggesting familiarity with the sounds. The findings echo those of previous studies, and the researchers explain what makes the protocol of this study particularly solid.

They say that using constant infusion both during semi-wakefulness and under anesthesia allowed the scientists to discern the effects of the drugs from other potentially confounding effects. So far, this has been an obstacle to fully understanding whether anesthesia causes a complete loss of consciousness or not.