Detecting consciousness in a totally locked-in patient

Alert to your surroundings but helpless to respond. It's difficult to imagine a worse situation, but this is the terrifying reality for a minority of brain damaged patients with total locked-in syndrome. Fortunately, researchers are developing ways to reveal consciousness trapped inside a lifeless body. Such techniques will hopefully prevent conscious, yet utterly paralysed, patients from being misdiagnosed as comatose.

In this new study, Caroline Schnakers used bed-side electroencephalography (EEG) to detect consciousness in a 21-year-old woman who fell into a coma-like state following a stroke. Twenty-five, 39 and 49 days after her brain was damaged, the researchers uttered the woman's own name to her, together with a short list of irrelevant names, all the while recording the surface electrical activity of her brain with EEG. The important twist was that they sometimes instructed her to pay special attention to her own name, or to one of the unfamiliar names.

During the first two testing sessions, the woman's brain recordings betrayed no signs of awareness. On the third session, however, when she was instructed to pay special attention to her own name, the woman's EEG signal showed an exaggerated P300 response to her name, compared with when she was instructed to just listen passively. The P300 is a spike of activity recorded from the parietal lobe, which is thought to be a marker of consciousness or decision making. This suggests the woman had heard and heeded the task instruction - a sign that she was conscious inside her paralysed body. Fourteen days later, she began to show behavioural signs of awareness, for example by moving her finger in response to instructions.

The researchers said: "In conclusion, this active auditory event-related paradigm (requiring explicit comprehension of auditory-verbal instructions) provides an interesting tool for detecting voluntary brain activity in patients that behaviourally would be diagnosed as comatose". More research is now needed to validate this procedure, they added.

The new case-study comes after research published in 2006 that used functional brain imaging to detect consciousness in a patient in a persistent vegetative state. The EEG used in the current study has the advantage that it can be administered bed-side.
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Schnakers, C., Perrin, F., Schabus, M., Hustinx, R., Majerus, S., Moonen, G., Boly, M., Vanhaudenhuyse, A., Bruno, M., & Laureys, S. (2009). Detecting consciousness in a total locked-in syndrome: An active event-related paradigm. Neurocase, 15 (4), 271-277 DOI: 10.1080/13554790902724904

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