It should be mentioned that there is a highly controversial paper out in this week’s Science. Here, a study by Dr Adrian Owen shows that a patient that meets the criteria for vegetative state shows what can be thought of as signs of conscious life. You can see the MindHacks coverage of this story here. basically, the researchers asked their patient to imagine playing tennis or moving around her home and found that:
the patient activated predicted cortical areas in a manner indistinguishable from that of healthy volunteers
The researchers take this as a sign of the patient being conscious while still being unable to communicate, let alone perform any volutary behaviour. In this sense, it seems that the patient rather meets the criteria for locked-in syndrome. The study thus raises the question of whether this patient — indeed, any PVS patient — is conscious, and whether the diagnostic criteria are yet poorly defined and the symptoms similarly poorly understood.
Nevertheless, it should be considered an open question whether we should accept this finding as a true sign of consciousness in the patient. This is also covered nicely in a comment by Naccache in the same issue of Science. Pointing out some of the shortcomings of this study, as well as contrasting it to the many studies showing specific changes in PVS contrasted to normal consciousness, Naccache concludes:
Though not totally convincing on the issue of consciousness, the Owen et al. work paves the way for future functional brain-imaging studies on comatose and vegetative state patients. One can imagine probing each of the psychological properties of conscious processing listed above, and even trying to collect subjective reports by modifying the experimental paradigm.
As I have written earlier, this is indeed the case: we do not have a clear concept of the distinctions between coma, vegetative states, minimally conscious states or locked-in syndrome. Only during the past few years we have seen a dramatic increase in our understanding of these disorders. It is no doubt that our understanding will increase in the same manner during the next many years.
I have asked Dr. Owen and his co-author, Steven Laureys about this finding, and hope to get back to you with their replies shortly. In the meantime, you might be interested in this article (PDF) that Laureys and I co-authored with prof. Bernard Baars in TINS.
UPDATE: Nature has a podcast interview with Dr. Owen here.