EEG finds consciousness in people in vegetative state

Signs of consciousness have been detected in three people previously thought to be in a vegetative state, with the help of a cheap, portable device that can be used at the bedside.

"There's a man here who technically meets all the internationally agreed criteria for being in a vegetative state, yet he can generate 200 responses [to direct commands] with his brain," says Adrian Owen of the University of Western Ontario.

"Clearly this guy is not in a true vegetative state. He's probably as conscious as you or I are."

In 2005, Owen's team, used functional MRI to show consciousness in a person who was in a persistent vegetative state (PVS), for the first time.

PVS is also known as 'wakeful unconsciousness', whereby the body still functions but the mind is unresponsive.

However, fMRI is costly and time-consuming, so his team set about searching for simple and cost-effective solutions for making bedside diagnoses of PVS.

Now, they have devised a test that uses the relatively inexpensive and widely available electroencephalogram (EEG).

An EEG uses electrodes attached to the scalp to record electrical activity in the brain.

Imagine wiggling your toes
Owen and his team used an EEG on 16 people thought to be in a PVS and compared the results with 12 healthy controls while they were asked to imagine performing a series of tasks.

Each person was asked to imagine at least four separate actions – either clenching their right fist or wiggling their toes.

In three of the people with PVS, brain regions known to be associated with those tasks lit up with activity, despite physical unresponsiveness.

This suggested to the researchers that the subjects were carrying out a complex set of cognitive functions including hearing the command, understanding language, sustaining attention and tapping into working memory.

"It isn't the case that just because somebody doesn't respond they're not conscious," Owen says. "There's a growing body of data now demonstrating that many of these patients aren't what they appear."

Criteria of Vegetative State (PVS)
"The diagnostic criteria for vegetative state have to change," he adds. The official diagnosis for PVS was formulated in the 1970s, before neuro-imaging was widely used, says Owen.

The last update was made in 1995, but the criteria for declaring someone conscious is still based on whether an outside observer believes the patient is trying to communicate.

Morten Overgaard, a cognitive neuroscientist at Aalborg and Aarhus University in Denmark, says that determining whether Owen's patients are actually responding consciously or whether they are unconsciously reacting to suggestions from the command is difficult to know without further study.

"If this is suggested as a standalone test to decide whether a person is conscious or not, then we need [signs] that are very strong and not just an indication of consciousness," he says.


Absence of Awareness
The test cannot prove the absence of awareness, but it can identify people who weren't thought to be conscious, says Damian Cruse, a collaborator on the study.

This was particularly apparent when 25 per cent of the healthy controls returned EEG readings that were below expected levels of conscious thought.

Communicating with carers
However, for those people previously considered to be unaware of their surroundings, communicating with their caretakers through EEG tests could change their life. "We're trying to work out how to use this technique to find out more about somebody's internal mental state," says Owen. "It opens up the possibilities for potentially facilitating recovery. If you have a channel of communication with a patient, you can have that patient play a role in therapeutic intervention."