This discusses brain imaging and diagnosing lack of consciousness...
The problem is that the press has called people in "persistant vegetative state" as "in a coma"...when they open their eyes, follow you when you are nearby, respond to pain etc they are not in a coma...indeed, an old study showed 40 percent of those diagnosed as "pvs" by neurologists (i.e. after a one or two hour examination) were not PVS according to caretakers. In other words, it's a trash can diagnosis, similar to the old "schizophrenia" diagnosis before the DSM-4 divided it into different catagories...
The second problem is that the underlying idea behind the entire discussion is not mentioned: The idea that if one lacks "consciousness" then you are essentially dead, and therefore we can kill you either by starvation (one prominent neurologist named Cranford said even spoon feeding people with PVS is optional medical treatment...which is why they did not allow Terri Schiavo to go thru a swallowing rehabilitation program before removing her feeding tube)...
Knowing that some "ethicists" have long argued that infants, people with IQ's under 40, and senile people "lack the criteria for personhood", we should be very cynical about such things...
When the Dutch are killing infants legally, we should not shrug and say there is no danger of history repeating itself...