BRAE 213-F09 - HW#7 - Owen- detecting awareness in the veg state (2006) Science

BRAE 213-F09 - HW#7 - Owen- detecting awareness in the veg state (2006) Science

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Detecting Awareness in the Vegetative State Adrian M. Owen, 1 * Martin R. Coleman, 2 Melanie Boly, 3 Matthew H. Davis, 1 Steven Laureys, 3 John D. Pickard 2 T he vegetative state is one of the least un- derstood 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. Although the diagnosis depends crucially on there being no reproducible evidence of purposeful behavior in response to external stimulation ( 1 ), recent func- tional neuroimaging studies have suggested that B islands [ of preserved brain function may exist in a small percentage of patients who have been diagnosed as vegetative ( 2 ). On this basis, we hypothesized that this technique also may pro- vide a means for detecting conscious awareness in patients who are assumed to be vegetative yet retain cognitive abilities that have evaded detection using standard clinical methods. In July 2005, a 23-year-old woman sustained a severe traumatic brain injury as a result of a road traffic accident. Five months later, she remained unresponsive with preserved sleep-wake cycles. Clinical assessment by a multidisciplinary team concluded that she fulfilled all of the criteria for a diagnosis of vegetative state according to inter- national guidelines ( 1 ) E Supporting Online Ma- terial (SOM) text ^ . We used function- al magnetic resonance imaging (fMRI) to mea- sure her neural responses during the presentation of spoken sentences (e.g., B There was milk and sugar in his cof- fee [ ), which were com- pared with responses to acoustically matched noise sequences ( 3 ). Speech-specific activi- ty was observed bilat- erally in the middle and superior temporal gyri, equivalent to that ob- served in healthy vol- unteers listening to the same stimuli (fig. S1). Furthermore, sentences that contained ambigu- ous words (italicized) (e.g., B The creak came from a beam in the ceiling [ ) produced an ad- ditional significant response in a left inferior frontal region, similar to that observed for normal volunteers. This increased activity for ambiguous sentences reflects the operation of semantic pro- cesses that are critical for speech comprehension. An appropriate neural response to the mean- ing of spoken sentences, although suggestive, is not unequivocal evidence that a person is con- sciously aware. For example, many studies of implicit learning and priming, as well as studies of learning during anesthesia and sleep, have demonstrated that aspects of human cognition, including speech perception and semantic pro- cessing, can go on in the absence of conscious awareness. To address this question of conscious aware- ness, we conducted a second fMRI study during which the patient was given spoken instructions to perform two mental imagery tasks at specific points during the scan ( 3 ). One task involved imagining playing a game of tennis and the other involved imagining visiting all of the
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BRAE 213-F09 - HW#7 - Owen- detecting awareness in the veg state (2006) Science

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