When thoughts become actions: functional neuroimaging in the vegetative state

Abstract

The vegetative state is one of the least understood and most ethically troublesome conditions in modern medicine. The term describes a unique disorder in which patients who emerge from coma appear to be awake, but show no signs of awareness. The diagnosis is not normally considered until between 1 and 3 months post ictus, at which point there must be no evidence of sustained, reproducible, purposeful or voluntary behavioral response to visual, auditory, tactile or noxious stimuli. There must also be no evidence of language comprehension or expression, although there is generally sufficiently preserved hypothalamic and brain stem autonomic functions to permit survival with medical care. A number of recent studies have demonstrated that functional neuroimaging may have an important role in the identification of residual cognitive function in some patients who are assumed to be vegetative, yet retain cognitive abilities that have evaded detection using standard clinical approaches. So-called ‘activation studies’ have the potential to demonstrate distinct and specific physiological responses (changes in regional cerebral blood flow or changes in regional cerebral hemodynamics) to controlled external stimulation without the need