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Test 'detects consciousness level'

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Different states of consciousness in patients could be identified using a new brain test, researchers have claimed.

A specific neural “fingerprint” was detected by scientists in the brain responses of healthy volunteers and “minimally conscious” patients, but not those in a “vegetative” state.

Researchers combined electroencephalography (EEG), which measures electrical activity in the brain, with a sophisticated mathematical model to record their measurements.

Previous studies have indicated that patients who are severely brain damaged and display few outward signs of awareness may still have some perception of what is happening around them.

Better methods of measuring awareness could improve their treatment and pain control, and offer some comfort to loved ones.

The research team, from the University of Liege in Belgium, gathered EEG recordings from 22 healthy volunteers and 21 patients with severe brain damage.

Eight patients were “vegetative”, in a state of non-responsive wakefulness, and 13 “minimally conscious”, a condition in which there may be some deliberate movement such as eye-tracking.

None of the patients was in a coma, a state of deep unconsciousness lasting more than six hours.

Measurements were taken while subjects listened to a series of simple tones.

Previous studies have shown that the brain’s electrical response to the sound alters when there is a change in pitch. But this does not happen during sleep and under anaesthesia, suggesting that it may be an indicator of consciousness.

Both healthy volunteers and minimally conscious patients reacted to the changing tone frequency. However, only a fleeting response was seen in vegetative patients whose EEG readings altered for less than one-tenth of a second.

The research was reported in the journal Science.

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