Neuroimaging and the vegetative state: resolving the behavioral assessment dilemma?

The accurate assessment of patients with impaired consciousness following a brain injury often remains a challenge to the most experienced clinician. A diagnosis of vegetative or minimally conscious state is made on the basis of the patient's clinical history and detailed behavioral examinations, which rely upon the patient being able to move or speak in order to demonstrate residual cognitive function. Recently, the development of noninvasive neuroimaging techniques has fostered a rapid increase in the exploration of residual cognitive abilities in these patient populations. However, while this body of literature is growing rapidly, at present the enterprise remains one of scientific endeavor with no inclusion in standard clinical practice. Correctly administered behavioral testing in survivors of brain injury may provide sufficient information to identify patients who are aware and are able to signal that this is the case via a recognized motor output. However, it remains possible that a subgroup of these patients may retain some level of awareness, but lack the ability to produce any motor output and are therefore mistakenly diagnosed as vegetative. It is in this latter situation that functional neuroimaging may prove to be most valuable, as a unique clinical tool for probing volition and residual cognition without necessarily assuming that the patient is able to produce any motor output.