Capgras Syndrome describes the mental disorder whereby a person believes that a loved one or friend has been replaced by an imposter. The disorder is named after Jean Marie Joseph Capgras, the French psychiatrist who first identified it.

An example can be found in a case described in the Psychiatric Times of 40-year old Mary who believed that her 9-year old daughter had been taken by Child Protective Services and replaced by an imposter. “On occasion, she had shown up at her daughter’s school, refusing to pick her up, screaming, ‘Give me my real daughter; I know what you’ve done.'” Mary claimed that she’d see her real daughter with other people but she’d be whisked away.

Capgras is typically associated with an underlying brain disorder such as Alzheimers, dementia, schizophrenia or bipolar disorder. It can also occur in those with other types of brain injury or disease, such as a brain hemorrhage.

While the exact causes of Capgras delusions are not known, it is thought to occur when the thinking part of the brain recognizes a person but the emotional part of our brain doesn’t register the emotions we feel toward that person. Recognition relies on a balance of cognition and emotion and when there is a disconnect Capgras delusions can occur. Here’s a helpful illustration:

Stanford neuroscientist Robert Sapolsky describes this dual aspect of recognition well:

How do we identify a loved one? Well, he has eyes of a known color; distinctive hair texture; a particular posture; that scar on his chin from when he was a kid. Things we know. This is the purview of a highly specialized part of the primate brain, the fusiform gyrus, which recognizes faces, particularly those of significance.

But this is only half the story. How else do we identify the Significant Other? Well, we reimagine what it was like to hold her in our arms the first time; her scent from up close summons a thousand memories; we note her brief sardonic smile, knowing that it means she’s also bored by the dinner host. Things we feel. And this is the neurological purview of the “extended face processing system,” a diffuse network including a variety of cortical and limbic regions.

Source: Nautilus Magazine

In addition to believing a person has been replaced by imposters, Capgras can also occur in the context of pets – there are cases where people believe their dogs, cats or birds have been replaced with identical imposters.

Treatment of Capgras Syndrome depends on the underlying condition that may be causing the delusions but usually involves taking SSRIs or anti-psychotics and therapy. Unfortunately, only about 50% of those with Capgras improve with treatment.