What Happens in the Brain During Anesthesia?

Anesthesia is a procedure that ensures that the person is put to sleep during the surgery and does not feel pain. So how exactly does anesthesia take place and how does it affect the brain? Although it has a history of 170 years, what happens in the brain during anesthesia is one of the fields of medicine that preserves its mystery.

Anesthesia literally means insensitivity to pain. It is commonly used during surgeries, typically with gas or intravenous drugs. General anesthesia involves being put to sleep. In local anesthesia, the person is awake, but the nerve fibers going to a certain area are anesthetized and the feeling of pain is prevented.

The reason for loss of consciousness during general anesthesia is still a controversial issue. Although there are several theories to explain the effect of anesthesia on the brain, there is no consensus. Although it is one of the most commonly used medical procedures, it still has unknown properties. People do not dream during general anesthesia. There are people who claim to be dreaming, but these actually occur during awakening, not during anesthesia. The time period under the effect of anesthesia is almost erased from the memory.

How Does Anesthesia Work?

One of the interesting aspects of general anesthesia is that the same results can be achieved with many different anesthetic agents. Many drugs act through a specific binding site (receptor) in the body. Molecules with very different chemical properties in anesthetics cause unconsciousness.

It was previously thought that anesthetic agents bind to the lipid membranes of brain cells. The reason for this was that the anesthetic strength of the substances used was proportional to how much they were dissolved in oil. This view persisted until 1984. An experiment conducted that year showed that anesthetics can act without lipid membranes. It was later found that they actually interacted with protein receptors, specifically GABA . When GABA receptors are activated, the firing (signal production) of neurons in the brain slows or stops.

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In the textbooks of anesthesia, the part devoted to consciousness is very little, or even not mentioned at all in some old books. Instead of general neurophysiological mechanisms in the brain, events at the molecular level have been processed more. The effect of anesthesia has been explained through pharmacology. However, the neural circuits in the brain are also important. The trend has been changing in recent years. Research is proliferating to combine information at the molecular level with information at the electrophysiological and behavioral level.

During general anesthesia, it was thought that the brain was shut down like a light switch was turned off. However, electroencephalography studies that record brain waves have shown that electrical activity spreads throughout the brain under general anesthesia. It shows a different pattern from the waking state. In fact, the type of anesthetic agent used and the age of the person also affect the activity of the brain under anesthesia. Today, anesthetists look at parameters such as the patient’s blood pressure and heart rhythm, but EEG is not routinely used. Some researchers have suggested that with the routine use of EEG, the doses of drugs that should be given to patients can be determined more clearly.

Anesthetics that bind to GABA receptors suppress neurons, causing misfires in signal firing. This “misfire” disrupts the communication of different parts of the brain with each other. Since different areas of the brain cannot communicate with each other, it cannot know whether pain signals are coming from the body. Consciousness is turned off, but the electrical activity of the brain is not interrupted. Since the source of consciousness is not yet fully understood, the cause of loss of consciousness in anesthesia is not known exactly.

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The effect of anesthesia on the body occurs when the brain cuts off communication with the body. The brain cannot send movement orders to the muscles and cannot receive sensory signals from the body. Although the brain loses contact with every part of the body, breathing continues. The effect of anesthesia is likened to a coma.


Although general anesthesia is a complex procedure, it is quite safe. Still, it carries some serious risks. Aspiration pneumonia, which develops as a result of escaping the stomach contents into the lungs if the stomach is not empty, is one of them. To prevent it, the person should not eat or drink anything the night before the surgery. Other complications include allergic reactions and the development of a heart attack or stroke triggered by the impact of blood pressure.

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