This rare delusion convinces people their loved ones have been replaced by duplicates

We explore some of Wikipedia’s oddities in our 6,067,987-week series, Wiki Wormhole.

This week’s entry: Capgras Delusion

What it’s about: We’ve all heard of commonplace delusions—everyone’s out to get me, people are laughing at me behind my back, both sides in politics are equally bad—but there are some lesser-known and much stranger ones. Among them is the Capgras Delusion, a phenomenon where the sufferer believes a person close to them has been replaced by an identical duplicate. It’s an ideal setup for delusional thinking, as any evidence that the person is the genuine article is also evidence that the duplicate is really convincing.

Biggest controversy: There doesn’t seem to be a clear cause. While researchers believe Capgras stems from damage to the frontal lobe and/or the right hemisphere of the brain, it also tracks with paranoid schizophrenia and dementia. It’s been tied to an array of seemingly unrelated conditions including migraines, diabetes, and hypothyroidism. There’s also an isolated case of Capgras being brought on by the drug ketamine.

Strangest fact: Capgras may be a form of prosopagnosia (face blindness). In studying that phenomenon, researchers discovered that we recognize faces in two ways: conscious and unconscious. Prosopagnosia sufferers would subconsciously react to familiar faces they didn’t consciously recognize. The theory is that Capgras sufferers face the reverse—intellectually, they recognize a familiar person’s face. But they don’t make that subconscious connection, making something seem off about the person, creating the belief that while it looks like a familiar person, it’s not really them.

Thing we were happiest to learn: Capgras Delusion is extremely rare. However, even that has a downside, as because it’s so rare, it’s been difficult to study or to establish effective treatments. (Therapy and antipsychotic medication are the typical approaches.)

Thing we were unhappiest to learn: As little as we know about what causes Capgras, it took a long time before we knew even that much. The disorder was discovered in 1923 by French psychiatrist Joseph Capgras, describing a patient he referred to as “Madame Macabre.” As the delusion became well-known, it was assumed that it was a form of “hysteria” that only affected women (not true, although it seems to favor women by a 60/40 split), and that it was purely psychological. Even when doctors began seeing brain lesions in Capgras sufferers, they were dismissed as unrelated until the 1980s, when researchers began to consider that Capgras might have a physiological cause.

Best link to elsewhere on Wikipedia: Capgras effectively has an opposite. Fregoli delusion is another rare disorder in which the sufferer believes that many people in their lives are actually the same person in a series of disguises. (They often believe they’re being persecuted by this person.) Fregoli also seems to be related to face blindness and caused by injury to the brain.

Further Down the Wormhole: We were planning on jumping to a story about the Green Berets invading North Carolina, but the very first link on the way there was List Of Impostors, which was too good to pass up. We’ll do impostors next week, then the invasion. Stay safe, everybody!