The brain does not shutdown under general anesthesia but rather continues to have significant activity. The anesthetic agents used act directly on the brain, suppressing consciousness in a controlled and reversible way. Nonetheless, little is known about the actual mechanisms involved in general anesthesia. It is essential to understand more about this action in order to develop modern tools to monitor the brain during anesthesia, and to develop more selective anesthesia drugs.
In a study published in Anesthesiology, a team at NeuroSpin observed the brain of a non-human primate model in the conscious state and under general anesthesia, to establish a "universal brain signature" during general anesthesia, regardless of the drug used.
Béchir Jarraya, who led this research with Lynn Uhrig, explained: " To better understand the discovery, imagine that our brain is our planet earth and that the functional MRI is a satellite monitoring the roads. We found that, in the conscious state, the road network is fluid and flexible: traffic flows smoothly on the major highways and secondary roads and there is a great deal of flexibility in the management of changes in the flow encountered by the network. However, in the case of general anesthesia, the network is confined to motorways. It allows neither good flexibility, nor good flow distribution, generating traffic jams of sorts. That's how our team discovered a universal brain signature of general anesthesiaTo understand the discovery more easily, imagine that the brain is the planet Earth and that functional MRI is a satellite tracking the road networks. We found that, in waking state, traffic on the road network is fluid and flexible: traffic flows smoothly on the major highways and secondary roads and there is a great deal of flexibility in the management of changes in the flow encountered by the network. When under general anesthesia however, the network is restricted to the superhighways. Traffic flow is neither flexible nor evenly distributed, creating jams. This is how our team discovered that there is a universal brain signature for general anesthesia."
To achieve these results, the scientists induced general anesthesia in a non-human primate model, using a protocol very similar to that used to anesthetize patients in clinical routine, and recorded brain activity using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). Cerebral dynamics were studied using an algorithm used in statistical clustering to extract, from the fMRI data, the brain states specific to general anesthesia (see figure above).
This discovery could have a huge impact on monitoring and adapting general anesthesia for patients undergoing surgery, as well as for comatose patients requiring sedation in the intensive care unit.
The Collège de France, Hôpital Sainte-Anne and Hôpital Necker were also involved in this research.
Brain signature in the awake state (left) and under general anesthesia (right), established by a team at NeuroSpin. The team's observations show that brain activity in the waking state is rich and flexible: different areas of the brain, linked or not by anatomical connections can be activated simultaneously. Under general anesthesia, although still active, only those areas that are linked by direct anatomical connections can be activated simultaneously, thus making brain activity rigid and inflexible. © American Society of Anesthesiologists, 2018