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EEG used to detect awareness in vegetative patients

EEG_cap.jpgPosted on behalf of Mo Costandi.

A cheap and portable electroencephalography device can effectively detect consciousness in patients in the vegetative state, according to a new study published today in The Lancet.

The persistent vegetative state, minimally conscious state and coma are all disorders of consciousness, but distinguishing between them for an accurate diagnosis can be extremely difficult.

Patients in the vegetative state usually show no signs of awareness on commonly used behavioural tests, but it is now thought that approximately 40% of such patients are misdiagnosed and are in fact minimally conscious.

For the new study, Damian Cruze and his colleagues at the University of Western Ontario’s Brain and Mind Institute and his colleagues recruited 16 patients diagnosed as being in the vegetative state and 12 healthy controls.

All of the participants were asked to perform a simple motor imagery task in which they imagined either clenching and then relaxing their right fist or wiggling the toes on both feet whenever they heard a beep.

The participants’ brain function was assessed during the task using electroencephalography (EEG), which measures the electrical activity of the brain using electrodes attached to the scalp (pictured).

Three of the vegetative patients were found to be aware of the researchers’ commands and were capable of responding to them in the same way as the healthy controls.

The findings confirm earlier work showing that some vegetative patients are in fact conscious. They also show that EEG can be used to detect hidden signs of awareness in these patients and may help clinicians to diagnose them more accurately. Accurate diagnosis is important as each state is associated with a different outcome.

“Our device does not differ fundamentally from most other EEG devices,” says senior author Adrian Owen. “This means that existing devices in hospitals can be adapted to do what we did.”


The same team of researchers previously used functional magnetic resonance imaging (fMRI) to identify hidden signs of consciousness in vegetative patients, and to obtain simple ‘yes/no’ responses from them.

Scanning these patients’ brains with fMRI poses a number of difficulties, however. The technique is expensive, transferring patients into the scanner can be stressful for them and any small movements they make during the scan can confound the results obtained. Consequently, scanning is performed only on a very few patients with consciousness disorders.

The new system has several advantages over brain scanning. It is far cheaper and easier and could, therefore, give all such patients an opportunity to reveal that they are conscious.

“Our next goal will be to integrate our system with brain–computer interfaces to create a true communication system for patients who have no other means for communicating their thoughts and wishes,” says Owen.

Image credit: Wikimedia Commons

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    Adam Dickey said:

    The first author’s last name is Cruse, not Cruze

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