Cortical function in the persistent vegetative state.

expressed quantitative cerebral activity is crucial. The strongest evidence that supports the concept of early recovery of awareness in Menon et al.'s patient is that she ultimately recovered consciousness. Had she never regained any additional expressed qualities of attention, recognition, or interactive behavior beyond the P300 and the PET findings after another eight months (i.e. a year after the initial illness) she would have been diagnosed as permanently vegetative by most observers. In this setting, the notion that the PET activation might confer a degree of awareness would be substantially less compelling. Emphasis on selectivity of the response obtained in Menon et al.'s patient produces some additional concerns. The employed subtraction paradigm paired familiar face stimuli with images obtained by 'repixellating the photographs to remove structure from the images'. The ambiguity of separating faces from geometric non-faces prevents knowing the specificity or category of the response. For example, would familiar versus unfamiliar faces have led to a significant subtraction image? Is the response due solely to differences in spatial frequency content after the image-processing step? In any case, despite these ambiguities, the result marks a new and important observation using functional brain imaging to identify modular components in a severely brain-damaged patient. The abnormal P300 response in this patient is consistent with previous studies indicating that an intact P300 response improves the likelihood of recovery from coma or a vegetative state 5. As discussed below, the preservation of the P300 may also reflect the integrity of important brainstem and diencephalic structures. Of note, the P300 response in Menon et al.'s case report might correlate with receding edema or inflammation in the brainstem and thalamus, heralding recovery of these injured regions in their patient 6. Other evidence of preserved cortical processing in vegetative patients During the past four years, our laboratory has collaborated with Drs Rodolfo Llinas and Urs Ribary of New York University Center for Neuromagnetism, and an inter-institutional brain imaging team, to study a group of highly selected vegetative patients 2–4. Three particular patients, selected from 60 PVS cases, were reported to express remarkable behavioral fragments, not previously reported or observed by the authors. One of the three patients infrequently expressed isolated words (typically epithets) during a 20-year period of remaining in a PVS (Ref. 4). A second patient, over a period of many months without change, expressed continuous non-targeted movements during his wakeful periods, and a third patient …