How to Tell If a Brain is Awake: EEG May Not Always be a Reliable Reflection of Consciousness
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How to tell if a brain is awake: EEG may not always be a reliable reflection of consciousness:
Remarkably, scientists are still debating just how to reliably determine whether someone is conscious. This question is of great practical importance when making medical decisions about anesthesia or treating patients in vegetative state or coma.
Currently, researchers rely on various measurements from an electroencephalogram, or EEG, to assess level of consciousness in the brain. A Michigan Medicine team was able to demonstrate, using rats, that the EEG doesn't always track with being awake.
"EEG doesn't necessarily correlate with behavior," says Dinesh Pal, Ph.D., assistant professor of anesthesiology at the U-M Medical School. "We are raising more questions and asking that people are more cautious when interpreting EEG data."
Under anesthesia, an EEG will display a sort of signature of unconsciousness: reduced brain connectivity; increased slow waves, which are also associated with deep sleep, vegetative state and coma; and less complexity or less change in brain activity over time.
Building on data from a 2018 study, Pal and his team wanted to see what happened to these measures when a brain was awakened under anesthesia. To do so, they targeted an area of the brain called the medial prefrontal cortex, which has been shown to play a role in attention, self-processing and coordinating consciousness.
Using a drug in that part of the brain that mimics the activity of neurotransmitter acetylcholine, the team was able to rouse some of the rats so that they were up and moving around despite the fact that they were receiving continuous anesthesia. Using the same drug in the back of the brain did not awaken the rats. So, both groups of rats had anesthesia in the brain but only one group "woke up."
Then, "we took the EEG data and looked at those factors that have been considered correlates of wakefulness. We figured if the animals were waking up, even while still exposed to anesthesia, then these factors should also come back up. However, despite wakeful behavior, the EEGs were the same in the moving rats and the non-moving anesthetized rats," says Pal.
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