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University of Basel

12 May 2022

When unconscious, the brain is anything but "silent"

transparent 3D rendering of the brain
Despite acting on different receptors, located on different types of neurons, all general anesthetics lead to the loss of consciousness. Researchers have identified a common neuronal mechanism of anesthetic induced unconsciousness. (Image: iStock)

The cerebral cortex is thought to be the seat of conscious processing in the brain. Rather than being inactivated, specific cells in the cortex show higher spontaneous activity during general anesthesia than when awake, and this activity is synchronized across those cortical cells. Improving our understanding of the neuronal mechanisms of general anesthesia could lead to better anesthetic drugs and improved surgical outcomes.

In a paper recently published in Neuron, researchers from the group of Professor Botond Roska at the University of Basel and the Institute of Molecular and Clinical Ophthalmology (IOB) reveal how different cell types in cortex change their activity during general anesthesia, helping to understand how unconsciousness may be induced. 

You are lying on the operating table. The doctor tells you to count to 5, and places an anesthetic mask on your face. By the count of 4, you’ve lost consciousness. You will not wake up until after the surgery. What happened in your brain during this time?

One would probably assume that your brain has been silent. Especially your cortex, the brain area thought to be the seat of conscious processing. However, for close to 100 years, it has been known that some cells in the cortex are active and that cortex alternates between periods of high and low activity during general anesthesia.

Using EEG electrodes attached to the scalp is one of the few tools available to measure this activity, but electrodes don’t allow one to identify the cells underlying this activity. Therefore, the question has remained: which cells contribute to the rhythmic activity in the cortex, and how might that contribute to the loss of consciousness during general anesthesia.

On the trail of unconsciousness

Cortex is composed of different cell types, each with different functions. Different general anesthetics act on different receptors, located on different types of neurons, distributed throughout the brain. Yet, all general anesthetics lead to the loss of consciousness, and so “we were interested in finding if there is a common neuronal mechanism across different anesthetics”, says Dr. Martin Munz, one of the three first authors of the study.

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