Detecting awareness in ‘vegetative’ patients

Being trapped inside your own body, unable to move or communicate, is the stuff of nightmares. How does a medical practitioner or loved one know that you are not only alive but also aware?

You get labelled as being ‘vegetative’ – being without conscious awareness of self and environment – but as recent research has shown, sometimes this diagnosis is wrong.

Presently, MRI (magnetic resonance imaging) machines are used to detect awareness in unresponsive patients. However, these cannot be used if the patient suffers from involuntary movements (moving creates ‘noise’ in the MRI data that is processed into images) or they have metal pins and plates in their bodies (common in accident victims). In addition, the method requires specialist expensive equipment that is not always available, and the tests themselves are complex and expensive to perform.

Non-invasive way to detect conscious responses

Research published in the November 2011 issue of the medical journal Lancet shows that a simple, non-invasive and cheap method of detecting brainwave activity can identify conscious responses in some patients diagnosed as vegetative using official criteria. Indeed, of the 16 technically vegetative patients included in the study, three were able to give robust and reliable conscious responses to researchers.

The team of Canadian researchers used an electroencephalograph (EEG) brainwave test, using commands from an examiner to move either a hand or the toes to test for awareness. The patients weren’t actually able to move their limbs, but their brain reactions were compared with healthy control subjects who could. The team found that three of their group of 16 test subjects displayed brainwave changes consistent with appropriate ‘thinking’ on command, suggesting that these patients were not only aware but were attempting to follow the instructions.

The testing did not rely on one result to establish that these patients were aware. Each respondent consistently generated the requested mental states to command for a prolonged period within each trial and did so for several trials. One of the three patients produced consistently appropriate EEG responses for about 100 trials.

Advantages of using EEG

In their published research paper, the authors write that “the method described here could fundamentally change the assessment of this complex patient group because EEG is highly portable, inexpensive, can be done at the bedside, is available in most hospitals and can be used with patients who have metal implants ... EEG is [also] less affected by small motion artefacts [moving about], resulting in a drop-out rate of zero in our study ... The success of this technique also paves the way for development of brain/computer interfaces – or simple, reliable communication devices – in this patient group. Such devices will provide a form of external control and communication based on mappings of distinct mental states (for example, patients imagining right-hand movements to communicate ‘yes’, and toe movements to communicate ‘no’). The degrees of freedom provided by EEG could take this technique beyond binary responses to allow methods of communication that are far more functionally expressive, based on many forms of mental state classification. The development of techniques for the real-time classification of these forms of mental imagery will enable routine two-way communication with some of these patients, allowing them to share information about their inner worlds, experiences, and needs.”