3D movie reveals how brain loses consciousness

For the first time, a 3D "movie" has shown what happens in the brain when a person loses consciousness. The discovery could help to determine the state of consciousness of people with brain damage, and how fast they might recover.

Brian Pollard at the University of Manchester, UK, and colleagues used a new method called functional electrical impedance tomography by evoked response (fEITER) to record the brain activity of 20 people as they responded to a general anaesthetic.

The technique measures the resistance to a small current generated by electrodes on the scalp to gauge electrical activity in the brain. By taking 100 scans a second the team could create a real-time video of the activity of the whole brain. The results were presented last week at the European Anaesthesiology Congress in Amsterdam, the Netherlands.

The brain processes involved in consciousness are the topic of some debate. One theory proposes that people have a "seat" of consciousness – a brain region that activates or deactivates consciousness like a switch: "Click it and you're unconscious. Click it again and you're back on," says Pollard.

Another idea, put forward by Susan Greenfield at the University of Oxford, suggests that consciousness is generated by interactions between groups of brain cells. Inhibit this interaction and the person becomes sedated and then unconscious – rather like a dimmer switch.

The Manchester team's video shows that as anaesthetic takes hold, brain activity between certain clusters of neurons significantly increases. Pollard thinks this is probably a sign of inhibitory signalling between groups of neurons as the brain prepares to shut down. This supports the idea of neural assemblies. "If it were a switch, we would see one area light up then it would all go blank," Pollard says.

Geraint Rees at University College London says that this is an exciting advance, not least because the fEITER device is portable. For example, it might be used to record a signal from people with brain damage who are unable to communicate, to see how they respond to external stimuli.

Source New Scientist