UW – Madison researchers find a new way to accurately measure consciousness

Millions of people receive general anesthesia each year in the United States alone, but it is not always easy to tell if they are really unconscious.

A small proportion of these patients regain some awareness through medical procedures, but a new study of brain activity representing consciousness may have prevented that trauma. It may help both able-bodied people and scientists who are struggling to define which parts of the brain are said to be fundamental to the conscious mind.

What has been shown for 100 years in an unconscious state like sleep are these slow waves of electrical activity in the brain. But those may not be the right signals to use. Under a number of conditions – with a variety of anesthetic drugs, in people suffering from coma or brain damage or other clinical conditions – high-frequency activity is also possible. “

Yuri Saalmann, Professor of Psychology and Non-Psychology, University of Wisconsin-Madison

UW-Madison researchers recorded electrical activity in approximately 1,000 neurons around each of 100 sites across the brain of a pair of monkeys at the Wisconsin National Priority Study Center during several states of consciousness: under drug-induced anesthesia, light sleep , a relaxed awakening, and turned from anesthesia to a state of awakening through electrical stimulation of a deep spot in the brain (an approach described by the researchers in 2020).

“With data across several brain regions and different states of consciousness, we were able to combine all of these signals traditionally related to consciousness – including the speed or slowness of the rhythms of the consciousness. in different areas of the brain – with more computer measurements describing the complexity of the signals and how the signals in different areas interact, “says Michelle Redinbaugh, graduate student in an exam Saalman Laboratory and co-lead author of the study, published today in the journal Cellular systems.

To filter out the features that best reflect whether the monkeys were conscious or unconscious, the researchers used machine learning. They passed their large amount of data to a computer, told the computer what state of consciousness produced each pattern of brain activity, and asked the computer what areas of the brain and patterns of electrical activity most responsive to consciousness.

The results showed away from the frontal cortex, the part of the brain that was usually examined to safely maintain general anesthesia in human patients and the part most likely to exhibit the slow waves of activity that are being observed. ‘respect as usual is unconscious.

“In the clinic now, they may put electrons on the patient’s face,” said Mohsen Afrasiabi, another lead author of the study and an assistant scientist at Saalmann’s laboratory. “We suggest that the back of the head is a more important place for these electrons, because we are learning the back of the brain and the deep areas of the brain are more predictive of the state of consciousness than the face. “

And while both low activity and high frequency may be present in unconscious states, it is a complex that reveals an awakening mind.

“In an anesthetized or unconscious state, these probes in 100 different sites record a relatively small number of activity patterns,” says Saalmann, whose work is supported by the National Institutes of Health.

There was a larger – or more complex – range of patterns associated with the monkey’s awakening state.

“You need more complexity to provide more information, which is why it’s related to awareness,” Redinbaugh says. “If you’re not so complex across these important brain areas, they can’t provide much information. You’re looking at an unconscious brain.”

A more accurate measure of patients receiving anesthesia is one possible outcome of the new findings, and the researchers are working as part of a collaboration with support from the National Science Foundation. on applying knowledge to key areas of the brain.

“Beyond just detecting a state of consciousness, these observations could improve therapeutic outcomes from people with sensory disorders,” Saalmann says. “We were able to use what we have learned to maximize electrical patterns through precise brain stimulation and to help people who, say, in a coma maintain a constant level of consciousness. “