Is the Unconscious Brain Silent During Anesthesia?

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brain

The cerebral cortex is the outermost layer of the brain and has an association with the highest mental capacities. It is supposedly the seat for your brain’s conscious processing. During general anaesthesia, instead of being inactive, specific cells in the cortex show higher spontaneous activity. Furthermore, this activity synchronizes in the cortical cells. Understanding the neuronal mechanism of general anaesthesia will give a better understanding of anaesthetic drugs. In addition to better surgical outcomes.

Researchers from the University of Basel and Institute of Molecular and Clinical Ophthalmology revealed how the different cortex cell types change their activity during general anaesthesia, which helps in understanding the mechanism of inducing unconsciousness.

When you are going through a procedure under general anaesthesia, the doctor asks you to count to five. He puts on the anaesthetic mask and by the time you reach four, you have lost consciousness. You will not wake up till after the surgery but what happens to your brain during this period?

The general assumption is that the brain is probably asleep and silent. This is the assumption for the cortex specifically because it is the center of consciousness. It is known for more than a hundred years that the cortex cells are active between high and low activity. It happens when the patient is under general anaesthesia.

EEG Electrodes

The EEG electrodes are the tool to measure this ability by attaching it to the scalp. However, electrodes don’t identify the cells underlying this activity.

So, the main question remains. Which cells contribute to the cortex’s rhythmic activity and how do they contribute to loss of consciousness during general anaesthesia.

Consciousness Trail

The cortex has different cell types, and each cell has a different function. The different general anaesthesia act on different receptors that are in different types of neurons. They are present in the brain throughout. However, despite this, all the general anesthetics lead to loss of consciousness.

Dr. Martin Munz who is one of the first three authors of the study says,

“We were interested in finding if there is a common neuronal mechanism across different anaesthetics”

Modern Genetic Tools

Researchers use modern genetic tools in the Neuron publication, which is a combination of mouse lines. They label different cell types for addressing this question. Moreover, the previous susceptions were the opposite of one specific cell type in the cortex. Layer 5 pyramidal neurons showed increased activity when the animal had been exposed to different anaesthetics.

Dr. Arjun Bharioke from the research group says,

“Each anesthetic induces a rhythm of activity in layer 5 pyramidal neurons. Interestingly, these rhythms differed between anaesthetics. Some were slower, and some were faster. However, what was common across all anesthetics was that they all induced an alignment of activity. That is, when they were active, all layer 5 pyramidal neurons were active at the same time”

He further added,

“We called this ‘neuronal synchrony.”

The neurons of layer 5 serve as a major output centre for the cerebral cortex. Moreover, it also connects different cortical areas together to each other. Hence the communication is between both different cortical areas, in addition to the cortex to other areas of the brain.

Thus, the conclusion is that synchronization of activity across layer 5 pyramidal neurons restricts the output information of the cortex, which it can output.

Crowd Transition

Arjun said,

“It seems that instead of each neuron sending different pieces of information, during anesthesia all layer 5 pyramidal neurons send the same piece of information.”

Bharioke further said,

“One could think of this as when people in a crowd transition from talking to each other, for example before a soccer or basketball game, to when they are cheering for their team, during the game. Before the game starts, there are many independent conversations. In contrast, during the game, all the spectators are cheering on their team. Thus, there is only one piece of information being transmitted across the crowd.”

Disconnection of Cortex

According to the prior reports, loss of consciousness happens when the cortex disconnects from the other parts of the brain. The team also talked about the mechanism through which it happens. It is by the transition to the lower information output from the cortex when anaesthesia is given.

Alexandra Brignall said,

 “Anesthetics are very powerful, as anyone who has been in a surgery can attest to. But they are also not always easy to use. During a surgery, one has to continuously monitor the depth of the anesthetic to ensure that the patient is not too deep or too shallow. The more we know how anesthetics work and what they do in the brain, the better. Maybe this will help researchers develop new drugs to more specifically target the cells in the brain associated with unconsciousness.”

Botond Roska added,

“Our findings are highly relevant for medicine, since anesthesia is one of the most frequently performed medical procedures. Understanding the neuronal mechanism of anesthesia could lead to better anesthetic drugs and improved surgical outcomes.”

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Dr. Armash Shahab is a dentist with a bachelor's degree from Dow University of Health Sciences. She is skilled in general dentistry and is an experienced medical content writer. She also works as a Science Instructor for Little Medical School, which is a STEM-based learning program for kids. Her future plans are to work for the betterment of dentistry for the underprivileged in Pakistan, apply for postgraduation, and specialize in Paediatric Dentistry.

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