Detecting residual cognitive function in disorders of consciousness

Clinical audits have suggested up to 40% of patients with disorders of consciousness may be misdiagnosed, in part, due to the highly subjective process of determining, from a patient's behaviour, whether they retain awareness of self or environment. To address this problem, objective neuroimaging methods, such as positron emission tomography and functional magnetic resonance imaging have been explored. Using these techniques, paradigms, which do not require the patient to move or speak, can be used to determine a patient's level of residual cognitive function. Indeed, visual discrimination, speech comprehension and even the ability to respond to command have been demonstrated in some patients who are assumed to be vegetative on the basis of standard behavioural assessments. Functional neuroimaging is now increasingly considered to be a very useful and necessary addition to the clinical assessment process, where there is concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. In this essay, the latest neuroimaging findings are reviewed, the limitations and caveats pertaining to interpretation are outlined and the necessary developments, before neuroimaging becomes a standard component of the clinical assessment are discussed.