May 25, 2021

Each year in the U.S., millions of people receive general anesthesia, and a small proportion of those patients actually regain some awareness during their medical procedures.

A recently published study about brain activity representing consciousness could help prevent that potential trauma as well as help scientists define which parts of the brain are key to the conscious mind. Such information could lead to more accurate measurements of patients undergoing anesthesia, improve treatment outcomes for people who have consciousness disorders and help people in comas maintain a continuous level of consciousness.

Yuri Saalmann, a University of Wisconsin-Madison psychology and neuroscience professor, and his research team recorded electrical activity in about 1,000 neurons surrounding each of 100 sites throughout the brains of a pair of monkeys at the Wisconsin National Primate Research Center (WiNPRC). The researchers recorded activity during several states of consciousness: under drug-induced anesthesia, light sleep, resting wakefulness and roused from anesthesia into a waking state through electrical stimulation of a spot deep in the brain.

To sift out characteristics that best indicate whether the monkeys were conscious or unconscious, the researchers used machine learning. They input their large pool of data into a computer, told the computer which state of consciousness had produced each pattern of brain activity and asked the computer which areas of the brain and patterns of electrical activity corresponded most strongly with consciousness.

Surprisingly, the results pointed away from the frontal cortex, which is the part of the brain healthcare professionals typically monitor to maintain patient safety while under general anesthesia and the part most likely to exhibit slow waves of activity long considered typical of unconsciousness.

“In the clinic now, they may put electrodes on the patient’s forehead,” says Mohsen Afrasiabi, an assistant scientist in Saalmann’s lab. “We propose that the back of the head is a more important place for those electrodes because we’ve learned the back of the brain and the deep brain areas are more predictive of state of consciousness than the front.”

And while both low- and high-frequency activity can be present in unconscious states, complexity best indicates a waking mind. “You need more complexity to convey more information, which is why it’s related to consciousness,” says graduate student Michelle Redinbaugh. “If you have less complexity across these important brain areas, they can’t convey very much information. You’re looking at an unconscious brain.”

Read more about our consciousness research and how monkeys are helping improve patient care here.

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