Using functional magnetic resonance imaging to detect covert awareness in the vegetative state.

The assessment of patients with disorders of consciousness, including the vegetative state, is difficult and depends frequently on subjective interpretations of the observed spontaneous and volitional behavior. For those patients who retain peripheral motor function, rigorous behavioral assessment supported by structural imaging and electrophysiological findings is usually sufficient to establish a patient's level of wakefulness and awareness. However, it is becoming increasingly apparent that in some patients damage to the peripheral motor system may prevent overt responses to command although the cognitive ability to perceive and understand such commands may remain intact. Recent advances in functional neuroimaging suggest a novel solution to this problem; in several cases, so-called activation studies have been used to identify residual cognitive function and conscious awareness in patients who are assumed to be in a vegetative state yet retain cognitive abilities that have evaded detection using standard clinical methods.