If you ever had a surgery before, you definitely received anesthesia. An anesthesiologist told you to count backward from 100 and you soon drifted into a nice slumber. Several hours later, you woke up unaware as to what all happened during the surgery. My question is what exactly happens to the brain of the patient under anesthesia? This is something I have always wondered and decided to take the time to figure out.

Anesthesia, what is it? Are you really going to sleep or in a coma?

First thing to know before finding out what anesthesia does to the brain is to know exactly what it is. Anesthesia is a medicine that makes patients unconscious, immune to pain, and keeps them immobile during a surgical procedure. Research states that anesthesia is not a deep sleep as most doctors tell their patients. Dr. Emery Brown, a professor of anesthesia at Harvard Medical School and a practicing anesthesiologist as Massachusetts General Hospital, had numerous responses to this topic. He strongly emphasized in this article that general anesthesia, sleep, and coma have their similarities, but are very much different. Brown defines anesthesia unconsciousness as a “drug-induced, reversible condition (coma) that includes specific behavioral and physiological traits such as unconsciousness, pain numbing, and inability to move.” The sleeping brain throughout the night cycles through three stages of non-REM (rapid eye movement) sleep and alternates with REM sleep, which is when most dreaming occurs. Each of these have a distinctive EEG (electroencephalography) pattern, which reveal electrical activity in the brain. These patterns found not resembling the EEG of the brain under general anesthesia. General anesthesia activity was actually most similar to that of a comatose brain. Thus, the reasoning of which Brown emphasized that general anesthesia is a “reversible coma.” He said, “Sleep is not the state you’re going in, nor would it be the state in which someone could perform an operation on you. We need to perform a procedure very invasive to put you in a state which we can readily reverse.” Dr. Brown speaks with much detail on these similarities and differences in this video.

What happens to the Brain during general Anesthesia?

All people who received anesthesia wonder this question. Brown and his team have conducted imaging studies on volunteers under anesthesia to see how different parts of the brain change activity levels as the volunteers lose then later regain consciousness. Different drugs create different patterns in the brain. Propofol, for example, is one of the most widely used anesthetics that is a very strong (hypnotic) drug. It was later found that Propofol binds to GABA (which are involved in controlling sleep and alertness) receptors. The European Journal of Anesthesiology published a study in 2011 indicating that instead of suddenly switching off, consciousness actually fades away between the multiple parts of the brain (GABA). Brown spoke on how the receptors that the drug binds to are all over the brain and central nervous system.

Anesthesiologist often give patients anesthetics with an analgesic effect, which acts as painkillers. Other times they use the drug ketamine. In lower doses, the drug turns the brain highly active, and in higher doses, the brain does the opposite effect. Brown told how when the brain transitions through the active state, it frequently hallucinates or has a sense of euphoria. Ketamine does not induce anesthesia or forgetfulness, but instead blocks NMDA receptors, which are important to learning, memory, movement, and the neutral shape of the brain. The two drugs, Propofol and Ketamine, work together to calm patients and provide painkilling comfort during the surgical procedure.

Summary: 

Throughout my intensive research, I found out many things I did not know about anesthesia. The entire process is something that takes time and is very intricate. Anesthesia has more to it than spoken about. It is interesting to read that doctors are frequently mistaking “sleeping” for a few hours with anesthesia. The brain has so much happening to it all at once that people are thinking nothing actually happens to it. The fact that if there is a little under or over of Propofol and Ketamine could either relax or excite the brain during surgery is ridiculous. Dr. Emery Brown’s way of explaining how it is closer to comatose brain pattern makes all understanding of the brain under anesthesia clearer to understand. He speaks more over the subject in an interview here and gives great clarification for those who want more details. As I earlier stated with the count down from 100, I wanted to know why and how this works. Brown says here that, “You get a sense of how the drugs are affecting the brain from the count down. People rarely get beyond 90 because they stop remembering. If you think about it, we think of counting as a very simple process, but it’s actually fairly complex because you have to remember what you just said and then remember what the next number in the sequence is.” Then it all makes sense.