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 pathways of general anesthesia might lead to improved anesthetic drugs and improved surgical outcomes.
Researchers from the group of Professor Botond Roska of the University of Basel and the Institute of Molecular and Clinical Ophthalmology (IOB) have found how different cell types in cortex alter their activity during general anesthesia, thereby demonstrating how unconsciousness may be induced.
A doctor tells you to count to 5, and places an anesthesia mask on your face. By the count of 4, you have lost consciousness. You will not wake up until after the surgery. What happened in your brain during this time?
One might guess that your brain has been silent. It''s especially your cortex, the brain area that is thought to be the basis of conscious processing. However, for nearly 100 years, it has been known that some cells in the cortex are active and that cortex alternates between periods of intense and moderate activity during general anesthesia.
EEG electrodes attached to the scalp are one of the few methods available to measure this activity, but electrodes do not allow one to distinguish the cells that are involved in this activity. Therefore, the question remains: which cells contribute to the cortex''s rhythmic activity, 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. However, all general anesthetics lead to a loss of consciousness, and we were concerned about discovering if there is a common neural mechanism across different anesthetics, according to Dr. Martin Munz, one of the three first authors of the study.
The researchers used advanced analytical techniques to identify individual cortical cells types in thisNeuronpublication. These results showed that, contrary to what they had previously suspected, only one specific cell type within the cortex, layer 5 pyramidal neurons, showed a decrease in activity when the animal was exposed to different anesthetics.
Each anesthetic induces a rhythm of activity in layer 5 pyramidal neurons. Interestingly, these rhythms differed between anesthetics. Some were slower, and others were faster. However, all layers 5 pyramidal neurons were active at the same time, according to Dr. Arjun Bharioke of the same research group. This neuronal synchrony has been called.
Layer 5 pyramidal neurons serve as a major output center for the cerebral cortex and have linked different cortical areas to each other. This way, they communicate both between different cortical areas as well as from the cortex to other areas of the brain. Consequently, a synchronization of activity across layers 5 pyramidal neurons reduces the amount of information that the cortex can output.
Like a crowd at a soccer match
According to Arjun Bharioke, during anesthesia, layer 5 pyramidal neurons receive the same information. It''s possible that people in a circle transition from talking to each other, for example before a soccer or basketball game, to when they are cheering on their team. Hence, there is only one piece of information being transmitted across the crowd.
Prior research has suggested that the disconnection of cortex from the rest of the brain resulted in loss of consciousness. The results of the IOB team suggest a mechanism by which this may happen when the cortex is reduced during anesthesia.
Anesthetics are extremely powerful, as anyone who has been in an operation can attest to. However, they aren''t always easy to understand during an operation. The more we learn how anesthetics work and what they do in the brain, the better. Maybe this will help researchers develop new therapies to better address the unconscious cells in the brain.
According to Botond Roska, the author and director of the IOB Molecular Research Center, our findings are particularly pertinent for medicine. Anesthesia is one of the most frequently performed medical procedures.