Imagine looking at your mother, knowing in your gut that even though she looks exactly like your mother, moves and talks in the same way your mother does and has all the same habits, she just isn’t your mother. This is someone pretending to be your mother! Or your beloved pet, a dog you have had since he was a puppy and have come to know almost everything there is to know about, suddenly doesn’t appear to be himself. Your gut feeling tells you that despite appearances, this is not your mother or your dog. An evil suspicion begins to take shape, it simply must be an imposter, someone doubling as your mother or as your dog.
Just try to imagine how upsetting this experience must be for anyone living it.
The description above is not necessarily of someone totally psychotic. These are the feelings of someone suffering from a condition called Capgras syndrome. The patient may even see himself as his own double. It occurs as a result of brain injury, schizophrenia or dementia and can be transient or chronic. The phenomenon was first described in 1923 by Joseph Capgras, who called it “the illusion of doubles”.
Here is a video from YouTube were you can see a young man suffering from Capgras syndrome as a result of a car accident:
How can Capgras syndrome be explained?
Face-recognition takes place on several parallel levels. We must first recognize a face as an object, on another level we access biographic and semantic information evoked by this face, on still another level we respond to the face emotionally, we feel if it has a familiarity or not. Emotions, feelings of familiarity and biographic information might also come to mind by hearing the voice of the face’s owner or by a smell we have attached to this face.
So what goes wrong in the face-recognition process in Capgras syndrome? The explanation some of our leading scientists have proposed is built on the two-streams hypothesis. To recognize a face as an object, there would be a neural pathway from the visual cortex in the occipital lobe, to the temporal lobe (the ventral or what pathway) The identification process takes place in the fusiform gyrus of the temporal lobe. Another pathway goes from the visual cortex to the parietal lobe (the dorsal or where pathway). The dorsal pathway would project to the cingulate gyrus, but the cingulate gyrus is responsible for coordinating sensory input with emotions, so it is here the emotional response associated with familiar faces would arise.
In people with Capgras syndrome the ventral pathway would be intact, i.e. perception of the face is normal and the face gives rise to the appropriate memories but the dorsal pathway is damaged, so the face doesn’t evoke the emotional response it would normally do. Vision is normal, emotions are normal, but there is a disconnection between the two. The subjective feeling of familiarity is missing, making the patient feel something is terribly wrong. Some patients show the Capgras delusion only when in visual contact with the people they think of as imposters, but not when they talk to them on the phone. This is because the connections between his visual center and the emotional center is damaged, but not the connections between the hearing center and the emotional center. This is so cool, the brain is so totally, utterly perfect!
Capgras syndrome and prosopagnosia
Capgras syndrome is closely related to prosopagnosia, which was the topic of this post here. People with prosopagnosia are unable to recognize familiar faces. They might be able to recognize their mother from a group of strangers, but only from her voice, clothes, hairdo or gait. They cannot recognize faces, despite being able to recognize other objects. There seems to be some processing on the unconscious level however, as many people with prosopagnosia show higher skin conductance response to faces they are supposed to know, than to unfamiliar faces. In other words, they seem to be able to attach some emotional value to some faces, without consciously recognizing them. Some maintain the the Capgras syndrome is the opposite of prosopagnosia, i.e. prosopagnosiacs cannot consciously recognize faces but do so on some unconscious, emotional level but in capgras syndrome people recognize faces consciously but do not attach the unconscious emotional significance to them. In contrast to people with Capgras syndrome, the ventral pathway is damaged in prosopagnosiacs and the dorsal pathway is intact.
Hirstein and Ramaschandran (1997) claimed that the explanation above is to simple to fully incorporate all the evidence seen in Capgras syndrome, for example the fact that damages in the brains of Capgras patients are more often located in the temporal lobes (the ventral stream) than in the occipital and parietal lobes (dorsal stream). They propose instead that the cause of this syndrome is a disconnection in a pathway straight from areas in the temporal lobes to the limbic system, especially the amygdala. Here is Vilayanur Ramachandran, the rockstar of neuroscience, on Ted talk: http://www.ted.com/talks/vilayanur_ramachandran_on_your_mind.html
Finally I’d like to share with you this heartbreaking narrative from a website on Capgras syndrome:
Recently after she had an old shunt replaced, my wife of 32 years has recently been diagnosed with Capgras Syndrome. Which is connected in a way to the Radiation she received because of a brain tumor, and numerous surgery’s over the past 35 years. The sad part is she only knows she’s talking to me as her husband when she calls me on the phone. It sometimes includes her not recognizing her house but stating how amazing it is that it looks exactly like her real house. Not easy, but I try to let her think of me as a friend that her husband asked to take care of her. She keeps asking me where he is and if he has a girlfriend. It breaks my heart but she id the love of my life.
Gallego, L., Vázquez, S., Peláez, J. C., & López-Ibor, J. J. (2011). Neuropsychological, clinical and social issues in two patients with Capgras Syndrome]. Actas españolas de psiquiatría, 39(6), 408.
Hirstein, W. S., & Ramachandran, V. S. (1997). Capgras syndrome: A novel probe for
understanding the neural representation of the identity and familiarity of
persons. Proceedings of the Royal Society B: Biological Sciences, 264, 437-444.
Tranel, D., Damasio, H., & Damasio, A. R. (1995). Double dissociation between overt and covert face recognition. Journal of Cognitive Neuroscience, 7(4), 425-432.