A new study has revealed that humans are still somewhat conscious under the effects of general anesthesia. While they cannot feel any pain, patients given general anesthesia before an operation are still vaguely aware of what is going on around them. This is particularly true if there are noises or sounds that cause concern.
The experts found that 42 percent of patients under the influence of a general anesthetic can still be roused, while about half of those given a sedative can be easily brought to consciousness with a loud shout and physical contact.
Study author Antti Revonsuo is a cognitive neuroscientist and psychologist at the University of Turku in Finland.
“Nearly all participants reported dream-like experiences that sometimes mixed with the reality,” said Professor Revonsuo.
The investigation was focused on 47 healthy individuals who were given either the general anaesthetic propofol or the sedative dexmedetomidine until they were unconscious.
As the drugs were taking effect, the researchers attempted to rouse the participants. In addition, the experts recorded brain activity among the individuals throughout the trial.
Once the subjects were unconscious, the team played recordings that included sounds that were completely normal and others that included unusual sounds or sentences which ended abruptly.
The analysis of brain wave activity revealed that the individuals shifted between a deep sleep state and a state with much more awareness while supposedly unconscious.
Among individuals who were sedated, brain activity indicated that they heard the unusual sounds and attempted to interpret them. The participants under the influence of propofol did not acknowledge the odd sounds.
The presentation of unpleasant noises, however, got the attention of all the individuals, regardless of the drug used to sedate them. The participants were also found to react faster to these noises when they heard them while awake.
“In other words, the brain can process sounds and words even though the subject did not recall it afterwards,” said study author Harry Scheinin. “Against common belief, anaesthesia does not require full loss of consciousness, as it is sufficient to just disconnect the patient from the environment.”
The research is published in the journal Anesthesiology.