You're looking at a woman who resembles your mother. She moves and talks like your mother, and she's even dressed the same as your mother. In fact, she is your mother. But you're absolutely certain that she's an imposter.
This is the experience of someone suffering from a Capgras delusion, a rare medical disorder in which a person becomes convinced that a loved one has been replaced by someone pretending to be that loved one. The unsettling condition is the topic of this week's episode of Radiolab, entitled "Do I Know You?", and the show invited Dr Carol Berman and Dr V.S. Ramachandran on the program to talk about it.
No one knows exactly what causes Capgras delusions. The doctors cite one example in which the delusions started after a coma and another in which they came in the midst of more general dementia. But they can also start out of the blue. This is, to be sure, a terrifying prospect.
Dr Berman, a psychologist, hypothesises that Capgras delusions are an individual's way of dissociating a loved one from some perceived flaw - some sort of psychotic denial. This woman is being cruel, and I know my mother to be kind, so this must be an imposter.
Dr Ramachandran, luxuriously rolling his "r's", suggests that the delusions are caused by faulty circuity in the brain. We identify our loved ones, he says, by their familiar faces but also by the familiar emotions they evoke. If our brain no longer registers those emotions, we deem them an imposter. This woman looks like my mother, but she doesn't make me feel the way my mother makes me feel, so this must be an imposter.
Often times, the individuals subject to the delusions are perfectly normal otherwise. And the conditions that trigger the episodes are oddly narrow. If a person subject to Capgras illusions talks to the loved one on the phone, he recognises who she is and carries on normally. It's only in seeing her that the break occurs.
Over the course of the week we've looked at many ways in which memory - human and otherwise - is fallible. But hearing about Capgras delusions and the individuals who suffer from them serves to remind that some memories are more essential than others. [RadioLab]
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Memory [Forever] is our week-long consideration of what it really means when our memories, encoded in bits, flow in a million directions and might truly live forever.