Media playback is unsupported on your device Media caption These images capture a patient's brain activity the moment they slip into unconsciousness

For the first time researchers have monitored the brain as it slips into unconsciousness.

The new imaging method detects the waxing and waning of electrical activity in the brain moments after an anaesthetic injection is administered.

As the patient goes under, different parts of the brain seem to be "talking" to each other, a team told the European Anaesthesiology Congress in Amsterdam.

But they caution that more work is needed to understand what is going on.

The technique could ultimately help doctors pinpoint damage in the brains of people suffering from stroke and head injury.

"Our jaws just hit the ground," said anaesthesiologist Professor Brian Pollard from Manchester Royal Infirmary on seeing the images for the first time.

"I can't tell you the words we used as it wouldn't be polite over the phone."

Cross talk

Although regions of the brain seem to be communicating as "consciousness fades", Professor Pollard cautions that it is early days and that he and his team from the University of Manchester still have many brain scans to analyse before they can say anything conclusive about what is happening.

The finding supports a theory that is championed by Professor Susan Greenfield, from the University of Oxford, that unconsciousness is a process by which different areas of the brain inhibit each other as the brain shuts down.

Fully operable

The new technique, called Functional Electrical Impedance Tomography by Evoke Response (fEITER), is more compact than other brain imaging techniques, such as functional magnetic resonance imaging (fMRI), and so is easily transported into the operating theatre.

It involves attaching tens of electrodes to the patient's head, which send low electrical currents through the skull. The currents are interrupted by the brain's tissues and electrical signals.

Professor Pollard explained that the brain's structures should not change over a minute-long scan, and so any differences that he and his team see as the patient falls asleep must therefore be due to changes in their brain's activity.

It is hoped that this technique could be used to learn about the nature of consciousness, but it is also likely to help doctors make headway in monitoring the health of a person's grey matter after they have suffered a head injury or stroke.