A new study by scientists in England and Belgium has demonstrated that some patients thought to be in persistent vegetative state (PVS) have the ability to consciously respond to stimuli.
There are several different levels of impaired consciousness and diagnosing them is difficult. Previous research showed that over 40% of PVS patients studied had actually been misdiagnosed and would more appropriately be categorised as being in a minimally-conscious state. People classed as minimally conscious show some clear evidence of awareness and responsiveness.
The latest research studied 54 patients at centres in Cambridge, England, and Liege, Belgium, including 23 in PVS and 31 in a minimally-conscious state. A technique called functional magnetic resonance imaging (fMRI) was used to assess their ability to generate meaningful responses to two mental-imagery tasks. In one of the tasks, the patients were asked to imagine playing tennis, while in the other they were instructed to visualise walking around their home or a familiar city.
Five of the patients, including four thought to be in PVS, were shown to have activity in the brain areas responsible for the tasks, demonstrating evidence of conscious awareness where there had previously been none. One even correctly answered five of six questions by visualising playing tennis for 'yes' and navigating to their home for 'no'. The results show that a small proportion of patients thought to be unresponsive could in fact have some form of conscious awareness and a diagnosis of PVS for these patients would be unsuitable.
In the future, the fMRI technique could be used to detect signs of awareness that bedside assessments of behavioural response are unable to pick up. This could have a significant impact on the treatment provided to these patients. For example, they could be asked if they are feeling any pain in order to decide whether to administer painkillers.
Further research is required in order to determine how common this type of awareness is and how much insight into their situation the patients retain.
Reference
Monti, M, et al (2010). Willful modulation of brain activity in disorders of consciousness. The New England Journal of Medicine. Published online at www.nejm.org, 3 February 2010.
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