The Secret of General Anesthesia: How Does Human Consciousness Turn Off?

While surgical interventions were performed while patients were fully awake for most of human history, the introduction of general anesthetics into medicine in 1846 was a turning point.

Today, more than 350 million surgeries are performed under general anesthesia every year. A wide range of anesthetic substances, from the rarely used inert gases such as xenon to the widely preferred propofol, cause temporary loss of consciousness. The focus of scientists is on how these drugs, which generally reduce brain activity and prevent nerve cells from communicating with each other, make people sleep.

THE ROLE OF THALAMUS AND BRAIN SHELL

Nick Franks, professor of biophysics and anesthesiology at Imperial College in London, draws attention to the presence of regions that are disabled in the first stage in brain scans. Franks makes the following assessment, emphasizing the importance of the thalamus, which is located deep in the brain and plays a critical role in initiating sleep:

"Even if the entire brain is disabled, the brain has such a dense network of connections within itself that it is very difficult to distinguish and determine exactly what triggers this general pause. However, if you anesthetize an animal and then stimulate a specific area of the thalamus, you can wake the animal. Research also shows that some people in a coma can be awakened by stimulating the thalamus. Therefore, this is a critical region for the state of wakefulness."

While research continues to understand exactly how the process works, some scientists argue that the cerebral cortex, which is considered the main center of consciousness, is the main target. It is stated that areas such as the frontal lobe, which is responsible for critical thinking, and the parietal lobe, which processes sensory information, are also directly affected by anesthesia.

THE 'THIRD STATE' OF CONSCIOUSNESS AND BRAIN NETWORKS

On the other hand, the phenomenon of "accidental awareness", in which one in every 15 thousand patients can remember some moments during surgery, brings different dimensions of consciousness to the agenda. Jaideep Pandit, an anesthesiologist at Oxford University, stated that even though patients do not feel pain during surgery, they can move their fingers on command, pointing to the existence of a "third state of consciousness" between wakefulness and unconsciousness.

Neuroscientist Andrea Luppi from the University of Cambridge, in her research using fMR scans, found that the functional connectivity of anesthetized brains decreased and they lost their individual uniqueness and resembled other primate brains. According to Luppi, anesthesia virtually collapses a country's communication network by interrupting the interaction of distant parts of the brain and drags the flow of consciousness into an uncontrolled course.