Brain imaging and PVS: How excited should we be?

How exciting is the new research on the consciousness of patients diagnosed as in a persistent vegetative state (discussed here)? From a scientific point of view, this is an important piece of research. The ability to respond to yes/no questions is surely a reliable indicator of consciousness; once we have identified patients who can pass this test, we can begin to conduct other tests, to see whether the results correlate. We can begin to see whether the evidence of electrical activity in the brain in response to words or to physical discomfort reflect consciousness or are merely indicators of unconscious activity.  The new research also might have great diagnostic value. But we must be careful not to overinterpret the results.

Adrian Owen, one of the researchers involved (and whose work on detecting neural correlates of instruction following the study built upon) is reported today as having said that the research gave evidence of “a fully functioning mind”. Now, I am unsure whether Owen used these words at all (the reports do not give us a direct quotation from him), but if he did, he did not mean what they might appear to suggest. He is not suggesting that some PVS patients are actually in a locked-in state, in which normal consciousness is preserved. As he explains in the video here, we do not know just how much is preserved of the patient's cognitive ability. The ability to answer yes/no questions, which the study demonstrated, is sufficient for a diagnosis of minimally conscious state (MCS). But MCS is nothing like normal consciousness: consciousness in it is often transitory and may be quite low quality (perhaps something like the consciousness we have in the moments immediately after waking from deep sleep). Given that the task is quite demanding, involving two stages and the ability to learn a method of communication, the evidence here is of MCS that is perhaps on the upper end of the continuum; still, it is not evidence that the person is still in there, if by the person we mean the ongoing set of psychological properties (memory, character, quirks). Given that MCS is relatively low quality, it is far from clear that being in this state is actually a benefit to the patient: it might be that someone in this state is worse off than someone is actually unconscious, as several of the contributors to this blog have suggested elsewhere.

 

 

In fact, the best way to think about this study may simply be to regard it as giving us a new diagnostic tool. We have long known how difficult it is to differentiate between PVS and MCS patients: given that MCS is transitory, absence of awareness during a clinical interview may not be evidence of absence of awareness at all times; moreover, since the behavioral criteria for awareness require bodily response – such as the ability to track a moving object with one’s eyes, or squeeze the examining physician’s hand – patients may fail these tests for reasons to do with an inability to translate their thoughts into movement, rather than absence of thought at all. The new technique might allow us to pick up some patients who were wrongly being diagnosed as PVS. As a new diagnostic tool, it is certainly valuable. It is therefore both scientifically and clinically exciting. But it is not – yet – a reason to rethink our entire approach to the difficult ethical issues concerning the continuation of life support for these patients. 

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