EEG Measures Awareness in Some 'Vegetative’ Patients

Study: 1 in 5 Patients Diagnosed as Vegetative Showed Brain Activity Response to Verbal Commands

Medically Reviewed by Laura J. Martin, MD on November 09, 2011

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.

In their earlier studies, the researchers used functional MRI to image the brains of vegetative patients, finding that some patients showed evidence of consciousness that could only be identified with the test.

One such patient was a man in his late 20s who had been in a coma for two years following a car accident before entering what was believed to be a persistent vegetative state.

The man appeared to be awake and blinked occasionally, but otherwise showed no signs of awareness.

Owen and colleagues asked him simple questions while his brain was being scanned. They instructed him to imagine playing tennis to answer “yes” to a question and imagine walking around his home to answer “no”.

They chose the two images because tennis movements activate regions at the top of the brain associated with spatial activities, while navigation activates areas at the base of the brain.

Using MRI, Owen’s group and another research team identified four patients out of 23 tested (17%) who seemed to be able to respond even though they had been diagnosed as being in a vegetative state.

1 in 4 Study Participants Without Brain Damage ‘Failed’ Test

The new study, published in The Lancet Online First, was conducted to determine if EEG testing, which is much cheaper and easier to administer than functional MRI, could also detect awareness in seemingly unaware patients with brain damage.

It included 16 patients thought to be in vegetative states and 12 people who had no brain damage who served as a comparison group.

This time Owen, Cruse, and colleagues used imagery of movements to assess EEG responses, asking patients and healthy study participants to imagine moving their right hand and toes to respond to different commands.

Cruse tells WebMD that three of the patients, or 19%, generated the appropriate EEG responses to the two different commands more times than would have been expected by chance.

One in four of the healthy study participants, the ones with no brain damage, did not do as well, and were not able to consistently generate the appropriate electrical activity patterns.

Schiff says this finding casts serious doubt on the ability of EEG testing to provide meaningful clinical information about the consciousness of patients in vegetative states.

"The fact that only three-fourths of the normal subjects showed the signals suggests to me that the sensitivity of this test would be too poor to even try in the clinical setting," he says.

Schiff agrees that better tools are needed to evaluate consciousness in patients with brain damage who are unresponsive, but he adds that these patients are not being evaluated as aggressively as they should be with existing diagnostic tools.

"It is clear that we are missing -- by a wide margin in some cases -- the level of function of many patients evaluated with bedside exams," he says. "But the real elephant in the room here is that there is absolutely no infrastructure for providing therapies to improve the level of function in these patients. [Vegetative] patients are a forgotten population.”

Show Sources


Cruse, D., The Lancet, Nov. 10, 2011.

Damian Cruse, PhD, neurologist, The Brain and Mind Institute, University of Western Ontario, London, Canada.

Nicholas D. Schiff, MD, neurologist; director, Laboratory of Cognitive Neuromodulation, Weill Cornell Medical College, New York City.

News release, The Lancet Online First.

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