Impostors, impostors everywhere. Or are they?

David was involved in a bad car accident. He sustained head injuries when he landed head-first on the ground. Seemingly, though, he was fine, retaining the capacity to talk and walk. But there was a problem. Whenever David saw his mother, he would say that she looks like my mother, but really, she is not my mother. She is another woman who is, for some reason, pretending to be my mother. She is an impostor.

In Capgras delusion, the sufferer will look at another person, and claim that that other person is an exact double—an impostor. Never mind the fact that this “impostor” has mannerisms, characteristics, the same voice, as the “original” person. To a Capgras delusion sufferer, these facts do not matter.

David also thought his father was an impostor. Sometimes, he would tell his father, “You know, I think you’d like to meet this guy. He’s so much like you. But he drives better; he doesn’t go so fast.” David would know that his father was his father, but he also believed that there was another man, just like his father. This other man was his father’s impostor.

David would say that his father’s “impostor” looked exactly like his father, but is adamant that it is not his father. You cannot convince David otherwise. When questioned about when he looked at the person who looked like his father, David said, “There is a difference in the fact that I know that the person happens not to be my father…I don’t expect things from that person as I would expect from my parents.”

Capgras delusion isn’t limited to faces, to people, but to animals as well. Delusions may even include objects.

For example, David was sure that the house he lived in was just an imitation. One day, he told his mother that he wanted to go to his house, to David’s house. So his mother took him outside, went around the building, back through the elevator (it was an apartment, not technically a house), and took him back into the apartment room. His mother told him, “This is your house.” David was placated. He looked around and agreed that the room, where he had been in before his mother took him around the building, was his actual house.

Things could get stranger. The Capgras delusion sufferer can think of their own selves as an impostor of their “real” self. The delusion isn’t confined to things beyond the person.

The etiology of Caprgras delusion is not known, but there are still some ideas. In the temporal lobes of our brains, there is an area dedicated to processing faces. It is possible that Capgras delusion sufferers have some sort of temporal lobe damage. Not only that, but some visual pathways project into the temporal lobe. When a face is seen, the visual pathway is activated, which then activates another pathway that projects to the amygdala, the center for emotional processing, including fear and aggression. When David saw his father, he was sure it was an impostor. But when he spoke to his father on the phone, David no longer thought of his father as an impostor; the man was now his actual father. This goes along with the idea that the delusion is associated with some sort of damage to the visual center, and its projections to the emotional centers of the brain.

There is laboratory evidence that in a Capgras delusion patient, the emotional reaction we get from seeing another person is missing when they look at someone.

Skin conductance measures are taken to determine a person’s emotional response to a stimuli. Skin conductance is what is behind the so-called lie-detector tests. When you exhibit an emotional response say, to an image or a sound, your skin momentarily becomes a better conductor of electricity. The skin conductance sensor (SCS) is also known as galvanic skin response to indicate this phenomenon.

When you are shown a picture of a loved one, your skin conductance changes, and it can be recorded. This is because a familiar face elicits an emotional response from you: it is physiologically arousing (arousal here indicating any sort of activation, not necessarily sexual arousal.)

But put a Capgras delusion sufferer in the same situation, and guess what? They don’t exhibit a physiological response. Their skin conductance doesn’t change, even if they are shown a picture of their mother, their spouse, a sibling, a best friend. There is no emotional significance.