Madison, Wes. Millions of people undergo general anesthesia each year in the United States alone, but it is not always easy to tell if they are truly unconscious.
A small percentage of these patients regain some consciousness during medical procedures, but a new study of brain activity that exemplifies consciousness could prevent that potential trauma. It might also help both comatose people and scientists who struggle to identify the parts of the brain that could claim to be the key to the conscious mind.
“What has emerged over the course of 100 years in an unconscious state like sleep are those slow waves of electrical activity in the brain,” says Uri Salem, professor of psychology and neuroscience at the University of Wisconsin-Madison. But these may not be the right signals to take advantage of it. Under a number of circumstances – with different anesthetics, in people who are comatose or with brain damage or other clinical conditions – there can be high-frequency activity as well. “
UW-Madison researchers recorded electrical activity in about 1,000 neurons surrounding each of the 100 sites in all brains of a pair of monkeys at the National Primate Research Center in Wisconsin during several states of consciousness: under drug-induced sedation, light sleep, and waking while at rest. And it was awakened from anesthesia to a waking state by electrical stimulation of a deep spot in the brain (a procedure researchers described in 2020).
“ Using data across multiple brain regions and different states of consciousness, we can aggregate all of these markers traditionally associated with consciousness – including how fast or slow brain rhythms are in different brain regions – with more computational measures describing the complexity of signals and how signals interact in different regions. “Saalman’s lab graduate student and co-lead author of the study, published today in the journal,” says Michael Redenbau, Cell systems.
To examine the characteristics that better indicate whether monkeys are conscious or unconscious, the researchers used machine learning. They turned over a large set of their data to a computer, told the computer the state of consciousness that produced each pattern of brain activity, and asked the computer which areas of the brain and patterns of electrical activity closely matched consciousness.
The results indicated away from the frontal cortex, a part of the brain that is usually monitored to safely maintain general anesthesia in human patients and the part likely to show slow waves of activity that have long been considered typical of loss of consciousness.
“In the clinic now, they can put electrodes on a patient’s forehead,” says Mohsen Afrasiabi, the other lead author of the study and an assistant scientist in Saalmann’s lab. “We suggest that the back of the head is a more important place for those electrodes, because we have learned that the back of the brain and deep brain regions are more predictive of the state of consciousness than the forehead.”
And while both low-frequency and high-frequency activity can be present in subconscious states, complexity is the best sign of awakening the mind.
“When sedated or unconscious, those probes at 100 different sites record a relatively small number of activity patterns,” says Salman, whose work is backed by the NIH.
A larger – or more complex – range of patterns has been associated with the monkey’s awake state.
“You need more complexity to convey more information, which is why it’s related to consciousness,” says Redinbaugh. “If you have less complexity across these important brain regions, they won’t be able to transmit much information. You’re looking at an unconscious brain.”
One of the potential outcomes of the new findings is more accurate measurements of patients under anesthesia, and the researchers are part of a collaboration supported by the National Science Foundation working to apply knowledge to key brain regions.
“In addition to simply discovering a state of consciousness, these insights can improve therapeutic outcomes for people with disturbances of consciousness,” Saalmann says. “We can use what we have learned to improve electrical patterns through subtle stimulation of the brain and help people in, for example, in a coma maintain a continuous level of consciousness.”
This research was supported by grants from the National Institutes of Health (R01MH110311 and P51OD011106), the Biological Science Foundation, and the Wisconsin National Center for Primate Research.
– Chris Barncard, [email protected]
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