Here is Dr. V.S. Ramachandran's theory again. I buy it. He is an evolutionary psychiatrist ... that isn't the exact term ... but I believe in evolution/adaptation. His BBC lectures were superb, they are summarized in his book
A Brief Tour of Human Consciousness -- a superb read.
http://www.bbc.co.uk/radio4/reith2003/lecture5.shtml
An excellent discussion of this by V.S. Ramachandran. This was discussed in the BBC Reith lectures and this is the transcript. The Lectures were adapted and made into the book "A Brief Tour of Human Consciousness"
http://www.bbc.co.uk/radio4/reith2003/lecture5.shtml
If you read nothing else, read this.
..... from Ramachandran's lecture... see link to all lectures....
"Now Capgras and Cotard are both rare syndromes. But there's another disorder, a sort of mini-Cotard's that's much more commonly seen in clinical practice (those of you here who are psychiatrists know this, or psychologists).
It's called Derealisation and Depersonalisation. It's seen in acute anxiety, panic attacks, depression and other dissociative states. Suddenly the world seems completely unreal - like a dream. Or you may feel that you are not real - Doctor, I feel like a zombie. Why does this happen? As I said, it's quite common.
I think it involves the same circuits as Capgras and Cotard's. You've all heard of the phrase, playing possum. An opossum when chased by a predator suddenly loses all muscle tone and plays dead. Why? This is because any movement by the possum will encourage the predatory behaviour of the carnivore - and carnivores also avoid dead infected food. So playing dead is very adaptive for the possum.
Following the lead of Martin Roth and Sierra and Berrios, I suggested Derealisation and Depersonalisation and other dissociative states are an example of playing possum in the emotional realm. And I'll explain. It's an evolutionary adaptive mechanism. Remember the story of Livingstone being mauled by a lion.
He saw his arm being ripped off but felt no pain or even fear. He felt like he was detached from it all, watching it all happen. The same thing happens, by the way, to soldiers in battle or sometimes even to women being raped. During such dire emergencies, the anterior cingular in the brain, part of the frontal lobes, becomes extremely active. This inhibits or temporarily shuts down your amygdala and other limbic emotional centres, so you suppress potentially disabling emotions like anxiety and fear - temporarily. But at the same time, the anterior cingular makes you extremely alert and vigilant so you can take the appropriate action.
Now of course in an emergency this combination of shutting down emotions and being hyper-vigilant at the same time is useful, keeping you out of harm's way. It's best to do nothing than engage in some sort of erratic behaviour. But what if the same mechanism is accidentally triggered by chemical imbalances or brain disease, when there is no emergency. You look at the world, you're intensely alert, hyper-vigilant, but it's completely devoid of emotional meaning because you've shut down your limbic system. And there are only two ways for you to interpret this dilemma. Either you say the world isn't real - and that's called Derealisation. Or you say, I'm not real, I feel empty - and that's called Depersonalisation.
Epileptic seizures originating in this part of the brain can also produce these dreamy states of Deralisation and Depersonalisation. And, intriguingly, we know that during the actual seizure when the patient is experiencing Derealisation, you can obtain a Galvanic Skin Response and there's no response to anything. But once he comes out of the seizure, fine, he's normal. And all of this supports the hypothesis that I'm proposing."
V.S. Ramachandran, M.D., Ph.D.