STEVEN LAUREYS
Coma Science Group, University of Liège, Liège, Belgium

Is there anybody in there? Brain function in disorders of consciousness

Patients in a vegetative state (VS) and minimally conscious state (MCS) continue to pose problems in terms of their diagnosis, prognosis and treatment. Consciousness is a subjective first-person experience which study has remained the field of philosophy for the past millennia. That time has finally changed and empirical evidence from functional neuroimaging is offering a genuine glimpse on the solution to the infamous mind-body conundrum. New technological and scientific advances offer the neurological community unique ways to improve our understanding and management of severely brain damaged patients. Good medical management starts by making a correct diagnosis. There is an irreducible limitation in knowing for certain whether any other being is conscious. Vegetative patients can move extensively and clinical studies have shown how difficult it is to differentiate reflex or 'automatic' from voluntary or 'willed' movements. This results in an underestimation of behavioural signs of consciousness and hence a misdiagnosis, estimated to occur in about one third to nearly half of chronically vegetative patients. PET and fMRI studies have not yet shown to be reliable markers of recovery of consciousness. However, they have permitted to reject the ancient view that vegetative patients are neocortically dead or a-pallic. A succession of neuroimaging data has shown cerebral activation in isolated and disconnected islands of 'lower level' cortices or 'pallium' in response to auditory, visual, somatosensory and noxious stimuli. Functional neuroimaging studies have also provided scientific evidence that residual brain function in VS is very different from the brain?s integrative capacity in MCS. These studies have confirmed that VS and MCS truly are different physiological entities. However, in the absence of a full understanding of the neural correlates of consciousness, even a normal activation in response to passive sensory stimulation cannot be taken as incontestable proof of consciousness. In contrast, repeated and prolonged activation in response to the instruction to perform a mental imagery task would provide undeniable evidence of voluntary task-dependent brain activity, and hence of consciousness. This groundbreaking approach was recently validated in healthy controls and has been successfully applied to identify conscious perception in a - so far unique - patient behaviourally diagnosed as being in a post-traumatic VS. Brain computer interfaces (BCI) permit communication via voluntary EEG control, without any motor involvement. Technological improvements in such devices now enable locked-in patients to control their surroundings in ways never possible before. BCI can not only be employed as a communication instrument in LIS but also as a diagnostic tool in disorders of consciousness. It is thrilling to witness the use of this powerful approach in the assessment of possible residual consciousness in patients clinically diagnosed as 'VS' or 'MCS'. The question of what it feels like to be minimally conscious has not yet been solved but the technology to at least try to answer the issue is now existing.

References:
The Neurology of Consciousness, Laureys S and Tononi G (Eds),
Academic Press, NY, 2008
The changing spectrum of coma Laureys S, Boly M Nature Clinical
Practice Neurology, 2008
Death, unconsciousness and the brain, Laureys S Nature Reviews
Neuroscience, 11 (2005) 899-909
Self-consciousness in non-communicative patients, Laureys S, Perrin F,
Brédart S Consciousness & Cognition, 16 (2007) 722-741
Perception of pain in the minimally conscious state with PET activation:
an observational study Boly M, Faymonville ME, Schnakers C, Peigneux P,
Lambermont B, Phillips C, Lancellotti P, Luxen A, Lamy M, Moonen G, Maquet
P, Laureys S Lancet Neurology, published online October 6 2008

back