Detecting Awareness in the Vegetative State

"One of the big questions in consciousness research is how do we tell when someone – or something – is conscious? There are a range of opinions, from ‘anything alive is conscious including bacteria’ through to people who think only “high” animals are conscious: so dogs and cats may be conscious, but spiders aren’t. And there are people who say that only people are conscious – or go even further and say, ‘Hang on, the only person each of us has access to the consciousness of, is ourselves. We actually don’t know if anyone but ourselves is conscious.’ We may act and behave as if all other people are conscious – and we’re hardwired to naturally believe so – but we don’t actually have direct access to that. So how do you know whether someone is conscious or not? And specifically, what if you look at someone who is non-responsive, and is diagnosed as being in a vegetative state? Can you be certain that they are indeed unconscious, that they don’t have an inner mental life, that they don’t understand what’s going on around them? Or even if for some reason their sensory input is cut off, and they don’t know what’s going on around them, maybe they’re still in there screaming ‘I’m alive!’ So this is one thing newer techniques might be able to answer. These researchers took a woman who had been in a vegetative state since being in a car accident and put her in an MRI scanner. They gave her two different kinds of instructions that involved mental imagery – which they say is something that only conscious people can do: they asked her to imagine either playing tennis or walking through her home. And they got her to respond: her brain responded in the same way that normal healthy people’s brains responded, showing a different pattern of activation to each type of imagery. So their conclusion was that she was conscious. No one disputes that the paper itself is fascinating. The question is, does this brain activity really indicate that she’s conscious? When we first read it in our journal club after it appeared, everyone said, couldn’t this just be evidence of how much the brain can do without consciousness? No one can say this isn’t actually unconscious brain activity. One of the limitations of functional MRI is that it’s correlational. You can’t infer from the brain activity itself that that activity is causing a behaviour – it’s just happening at the same time. Which means, in this case, that it could be happening without actually indicating any consciousness. So two commentaries were published, from the many criticisms that were made of the researchers’ claim. One was based on the fact that we already know a lot of semantic brain activity can be evoked by stimuli that we’re not aware of. For example, if you expose people to written words, subliminally, too fast to notice what was written, there will still be brain activity related to the meaning of those words. This is a different situation, of course, but it could very well be that brain activity is evoked by certain words and doesn’t necessarily indicate consciousness. So that’s what one commentary said: that maybe these are just areas of the brain that respond to the word tennis, or home or room. The other criticism was based on logic. The fact that we know that certain mental thoughts lead to certain brain activity does not imply the opposite, that certain brain activity means that you’re having certain thoughts. The researchers took conscious people and when they told them to think about tennis or walk through the rooms of their house, these were the areas that lit up. They concluded that if these areas light up, this means that someone is thinking about playing tennis or walking through the rooms of their house. That’s a logical fallacy, it’s like saying if all cucumbers are green, then everything green is a cucumber. That particular group of researchers, their work is fantastic: they do really interesting research. And just because you can’t get to a conclusive answer, doesn’t mean it wasn’t worthwhile. One of their responses was to say, OK, in order to infer from certain brain activity that it’s conscious, you have to be able to associate with some kind of decision-making. So the answer is we give the person several choices: if they’re conscious they can choose one thing and not the other. So they found more vegetative patients whose brains responded in this way, and they taught them to associate thinking about tennis or walking through the rooms of their house, with the answers ‘yes’ and ‘no’ to specific questions, questions that had nothing to do with tennis or walking through the rooms in their house – like, ‘Is your name so-and-so?’ That’s a newer paper that appeared only this year. With some patients. Again, one of the things you learn about science when you’re actually doing it is that it’s messy. You never get a really clear-cut, definite answer. What you get are data-points that are more consistent with one answer than with another. So not every vegetative state patient responds to these kinds of instructions, those who do may do so to different levels of success… But I chose this paper because it has now been the topic of a lot of discussion, and it really gets to the conceptual issue of how do we know if someone is conscious, or whether we can ever really know? The back and forth is fascinating."