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Brain & Nervous System Health Center

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EEG Measures Awareness in Some 'Vegetative’ Patients

Study: 1 in 5 Patients Diagnosed as Vegetative Showed Brain Activity Response to Verbal Commands
WebMD Health News
Reviewed by Laura J. Martin, MD

Nov. 10, 2011 -- Some patients thought to be in a vegetative state may later be assessed to have some level of awareness. Now researchers in Canada say they are able to detect consciousness in these patients cheaply and easily by measuring electrical activity in the brain.

The researchers used a portable electroencephalography (EEG) device to measure brain activity. They found that three of 16 patients thought to be in unconscious vegetative states were able to repeatedly generate EEG responses to two distinct commands, even though they were unable to communicate in any other way.

A 29-year-old man who had suffered a head injury three months earlier and was otherwise uncommunicative "answered" correctly more often than most study participants who had no brain damage.

Study: Brain Waves Measure Consciousness

Study co-researcher Damian Cruse, PhD, of The Brain and Mind Institute at the University of Western Ontario, says EEG testing has the potential to provide more accurate bedside evaluation of patients thought to be in persistent vegetative states.

It may even serve as a way to communicate with patients who seem to be completely unaware but may not be.

But a neurologist who also studies consciousness in vegetative patients remains unconvinced.

"What we have seen is experimental results from small studies and none of these results have been clinically validated," says Nicholas Schiff, MD, of New York City’s Weill Cornell Medical College.

Patients in vegetative states have usually "awoken" from comas, but they are thought to have no conscious awareness. They can usually open and close their eyelids and have periods where they are asleep and awake, but show no other signs of awareness.

When a patient with brain damage has remained in this condition for more than four weeks, they are typically considered to be in a persistent vegetative state. Patients who demonstrate brief periods of awareness are considered to be in a minimally conscious state.

Patients Answered ‘Yes’ and ‘No’

For more than a decade, neurologist Adrian M. Owen, PhD, and colleagues have been studying patients diagnosed as vegetative, first at the University of Cambridge in the U.K. and now at the University of Western Ontario.

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