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This Is Your Brain Under Anesthesia - WIRED
May 11, 2021 2 mins, 14 secs
That bugs Emery Brown, who does monitor his patients’ brain patterns when they are under.

“Most anesthesiologists don't think about it from a neuroscience standpoint,” says Brown, who is a professor of computational neuroscience at MIT and of anesthesia at Harvard Medical School, as well as a practicing anesthesiologist.

“And once you understand how to read these patterns, and you understand the neurophysiology behind them, you can dose your drugs better,” Brown says.

The work shows, for the first time, how individual neurons in multiple regions of the brain respond as they become flooded with the sedative, and that their impulses slow by 90 to 95 percent.

Every thought that crosses your mind has, literally, crossed your mind, as millions of neurons in different parts of the brain chatter with one another.

Miller, a professor of neuroscience at MIT’s Picower Institute who co-led the work with Brown.

“It does this at all frequencies, from 1 hertz to up to 100 hertz or more.” Brain waves recorded from the scalp on an electroencephalogram, or EEG, show the cross talk of neurons collectively firing waves of electrical impulses across the outermost regions of the brain, or the cerebral cortex, which is typically seen as the control center.

“Sights, sounds, feelings, are all operating together to create this unified experience of what we're doing, how we're feeling, what we're thinking in a given moment,” says Miller.

But to push the science further, he and Miller wanted to record different regions simultaneously as an animal slips in and out of consciousness.

“The drug goes everywhere, and it gets there in seconds,” Brown says.

(Neurons in a healthy, awake brain spike about 10 times per second. Under propofol, that frequency falls to once per second or less.) Brown wasn’t surprised; he’d seen these types of slow oscillations before in other animals, including humans.

“Kind of like an FM radio,” Miller says.

“They’re on the same channel, they can speak to one another.” Millions of neurons communicate this way, at many different frequencies.

“Propofol comes along like a sledgehammer,” Miller says, "and just knocks the brain into this low-frequency mode where none of that is possible anymore.".

“And communication is everything in consciousness,” Miller says.

Previous work has shown that deep brain stimulation can restore some limb control to a person with a traumatic brain injury, as well as the ability to eat.

“It was a bit of a gamble, a long shot,” Miller says.

In a second line of experiments, the researchers stimulated the thalamus with electrodes, using current comparable to what people receive as a deep brain stimulation treatment for Parkinson’s disease.

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