The BBC's Reith lectures are a series of learned and fascinating lay-oriented educational pieces about the relationship of the human brain to conciousness and cognition. They're proceeding on a weekly schedule, and the Beeb is posting the entire text of the lecture along with the full audio and video clips. The first installment, Phantoms in the Brain, conducted by V.S. Ramachandran, is up now. It's totally engrossing — there're about five science-fiction-novels' worth of material there.
A patient I saw not long ago who had been in a car accident, had sustained a head injury and was in a coma for about a couple of weeks. Then he came out of this coma and he was quite intact neurologically when I examined him. But he had one profound delusion – he would look at his mother and say "Doctor, this woman looks exactly like my mother but she isn't, she is an imposter".
Now why would this happen? Now the important thing is this patient who I will call David is completely intact in other respects. Now to understand this disorder, you have to first realise that vision is not a simple process. When you open your eyes in the morning, it's all out there in front of you. It's easy to assume that it's effortless and instantaneous but in fact you have this distorted upside down image in your retina exciting the photoreceptors and the messages then go through the optic nerve to the brain and then they are analysed in thirty different visual areas, in the back of your brain. And then you finally after analysing all the individual features, you identify what you're looking at. Is it your mother, is it a snake, is it a pig, what is it? And that process of identification takes place in a place which we call the fusiform gyrus which as we have seen is damaged in patients with face blindness or prosopognosia…
Now what's happened in this patient? What we suggest is that maybe what's gone wrong is that the fusiform gyrus and all the visual areas are completely normal in this patient. That's why when he looks at his mother, he says "oh yeah, it looks like my mother", but the wire, to put it crudely, the wire that goes from the amygdala to the limbic system, to the emotional centres, is cut by the accident. So he looks at his mother and he says – "hey, it looks just like my mother, but if it's my mother why is it I don't experience this warm glow of affection (or terror, as the case may be). There's something strange here, this can't possibly be my mother, it's some other strange woman pretending to be my mother". It's the only interpretation that makes sense to his brain given the peculiar disconnection.
(Thanks, Alaina!)
