Science Beyond the SciLi: Your brain under anesthesia

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How anesthesia works is “really, really simple”–at least according to anesthesiologist,  neuroscientist and statistician Emery Brown. He is a professor of medical engineering and computational neuroscience at MIT, and an anesthesiologist at Massachusetts General Hospital. Brown (the professor) came to speak at Brown (the university) on Thursday at the Presidential Colloquium Series ThinkingOut Loud (again, what is with this formatting?). Dr. Brown described how general anesthesia works and how it relates to our understanding of consciousness.

Anesthesia is a drug-induced state that is comprised of unconsciousness, amnesia, analgesia (the inability to feel pain) and akinesia (the inability to move). All of these also happen to be the symptoms of death–luckily, the final definition an anesthesia state is stability and control, allowing the state to be reversible. Being put under anesthesia is one of the most safe and and common clinical procedures.

Your brain activity can be tracked with EEG scans that record oscillations in brain signals. Slow oscillations are associated with a loss of consciousness under anesthesia.

When patients emerge from anesthesia, they first respond to the most salient stimulus, their name. Then, they respond to random words–such as “book chair,” in the study done on this topic–and then to tones. During this process, brain rhythms move from the front of the brain to the back, which can be seen in EEG scans from various parts of the brain. This process is known as anteriorization, and is key to determining the neural effects of anesthesia.

Anesthesia is often thought of as a drug-induced sleep. People often wake up from their colonoscopies and say, “That was a great sleep!” However, Dr. Brown stressed the distinction that sleep is not anesthesia, and anesthesia is not sleep. It’s just less scary for an anesthesiologist to tell you, “I’m going to make you go to sleep now,” than “I’m going to put you in a reversible, drug-induced coma.”

Though a patient may seem to have the same external symptoms when sleeping and when under anesthesia, the EEG oscillations for these two states are completely different. The rush of energy that colonoscopy patients experience after waking up was from the after-effects of the drugs, not from restorative sleep. Propofol, a common anesthetic, caused a dopamine release that gives you a kick of energy after waking up. This is similar to the effects of Ritalin, a drug commonly used to treat ADHD (and, less legally, to give students a boost in cognitive function before the SAT) that also releases dopamine.

General anesthesia has applications far beyond knocking people out for procedures. Ketamine, an anesthetic more commonly known as a horse tranquilizer and an illegal party drug, has been used in low doses to treat depression. Other anesthesia drugs have been shown to treat Parkinson’s disease, drug addiction, brain injury and schizophrenia, and they also have uses related to sleep, meditation and hypnosis.

After Dr. Brown’s talk, an audience member asked about whether certain groups of people have different responses to anesthesia. Dr. Brown responded, “Oh man, you should have been in the OR with me last Tuesday!” The woman he was anesthetizing for a gastric bypass surgery simply wouldn’t submit to the anesthesia. He had to triple the strength of her propofol dosage and apply another anesthetic in order to put her under, and after the surgery when they turned off the drugs, she bolted up and came to immediately.

There is also a myth that redheads are harder to anesthetize, but Dr. Brown didn’t confirm or deny this, saying that they haven’t yet pursued genetic avenues.

So while the basic workings of anesthesia are well understood, there are still many effects to be explored, and Dr. Brown is contributing to the understanding of many of these topics.

Check out the next Presidential Colloquium talk on “Killing Cancer with Nano,” which is sure to be another knock-out (pun intended).

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