Image: Dr. Damien Cruse demonstrates the EEG method used to detect consciousness (Photo courtesy of UWO).

A simple, bedside 25-electrode electroencephalogram (EEG) can accurately detect awareness in people thought to be in a vegetative state, according to a new study.

Researchers at the University of Western Ontario (UWO; London, Canada), the University of Cambridge (United Kingdom), the University Hospital of Liège (Belgium), and other institutions recruited 16 patients--5 with traumatic brain injury (TBI) and 11 without--diagnosed in the vegetative state, as well as 12 healthy controls. An EEG task involving motor imagery was used to detect command-following--a universally accepted clinical indicator of awareness--in the absence of overt behavior. Patients completed the task in which they were required to imagine movements of their right-hand and toes to command. The researchers then analyzed the command-specific EEG responses of each patient for evidence of appropriate, consistent, and statistically reliable markers of motor imagery, similar to those noted in the healthy, conscious controls.

The results showed that three (19%) of the 16 patients could repeatedly and reliably generate appropriate EEG responses to the two distinct commands, despite being behaviorally entirely unresponsive. No significant relationship was noted between the patients' clinical histories (age, time since injury, cause, and behavioral score) and their ability to follow commands. When separated according to cause, two (20%) of the five TBI and one (9%) of the 11 non-TBI patients were able to successfully complete this task. The study was published early online on November 10, 2011, in the Lancet.

“Despite rigorous clinical assessment, many patients in the vegetative state are misdiagnosed. The EEG method that we developed is cheap, portable, widely available, and objective,” concluded lead author Damian Cruse, PhD, of the University of Western Ontario, and colleagues. “It could allow the widespread use of this bedside technique for the rediagnosis of patients who behaviorally seem to be entirely vegetative, but who might have residual cognitive function and conscious awareness.”

Patients diagnosed as vegetative have periods of wakefulness, but seem to be unaware of themselves or their environment. Although functional magnetic resonance imaging (fMRI) studies have shown that some of these patients are consciously aware, issues of expense and accessibility preclude the use of fMRI assessment in most of these individuals.

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