It sounds like a nightmare. The idea of anesthesia wearing off in the middle of a procedure and suddenly getting an eyeful of your own insides. Thankfully, anesthesiologists are generally very good at their jobs. When they put you under, you’re not supposed to be awake or aware of anything. But according to new research published in Nature, that doesn’t necessarily mean every part of your brain is shut down.
Scientists have assumed that general anesthesia shuts down your higher-level brain activity, the parts associated with consciousness. But a team of researchers from Baylor College of Medicine found that even while patients were fully anesthetized, individual neurons in the hippocampus were still up and running, doing all of the memorization and learning stuff that the hippocampus is supposed to do.
Using high-density Neuropixels probes implanted in seven epilepsy patients undergoing surgery, researchers were able to monitor hundreds of individual neurons while patients were unconscious. They were played a series of sounds through headphones while under anesthesia and watched how the brain responded. The sounds included podcasts, stories, and different bits of human speech.
Your Brain Is Always Listening, Even Under Anesthesia
More than 70 percent of the monitored neurons reacted to sounds and could distinguish unusual tones from ordinary ones, or “oddball” tones as the researchers call them. The neurons even responded to the meaning and structure of spoken words. Some of the patterns they noticed were sophisticated enough to predict what kind of word was likely to come next in a sentence.
The brain, while completely knocked out, is still doing some surprisingly complex stuff. Even when fully anesthetized, language processing patterns looked roughly the same as they do in someone awake.
The researchers were sure to stress that the patients weren’t secretly conscious the whole time. They had no idea that the sounds were actually happening and had no memories of them afterward. Despite that, their brains were processing them all the same when they were knocked out. The brain keeps processing and learning even when it’s been chemically turned off. It’s incredible, if a bit eerie.
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