Capgras syndrome

The Capgras delusion or Capgras' syndrome is a rare disorder in which a person holds a delusional belief that an acquaintance, usually a close family member or spouse, has been replaced by an identical looking imposter. The condition in some cases is a direct result of brain lesion. Capgras delusion is classed as a delusional misidentification syndrome, a class of delusional beliefs that involves the misidentification of people, places or objects. Additionally Capgras delusion is termed a monothematic delusion because it has been shown to occur on its own outside of any other delusions.

Although Capgras is commonly called a syndrome, it may occur as part of, or alongside various other disorders and conditions, such as schizophrenia and neurological illness. Therefore some researchers have argued that it should be considered as a symptom, rather than a syndrome or classification in its own right.

Overview
It is named after Joseph Capgras (1873-1950), a French psychiatrist who first described the disorder in a paper by Capgras and Reboul-Lachaux in 1923. They used the term l'illusion des sosies (the illusion of doubles) to describe the case of a French woman who complained that various "doubles" had taken the place of people she knew. However, the term illusion has a subtly different meaning from delusion in psychiatry so "Capgras delusion" is used as a more suitable name.

This case is taken from a 1991 report by Passer and Warnock: Mrs. D, a 74-year old married housewife, recently discharged from a local hospital after her first psychiatric admission, presented to our facility for a second opinion. At the time of her admission earlier in the year, she had received the diagnosis of atypical psychosis because of her belief that her husband had been replaced by another unrelated man. She refused to sleep with the imposter, locked her bedroom and door at night, asked her son for a gun, and finally fought with the police when attempts were made to hospitalize her. At times she believed her husband was her long deceased father. She easily recognized other family members and would misidentify her husband only.

Causes
There is strong neuropsychological evidence that the Capgras delusion is, at least in part, related to a loss of emotional response to familiar faces. This is in the context of generally good (although not always perfectly intact) face perception abilities. This seems to be the reverse of prosopagnosia. In prosopagnosia, conscious face recognition abilities are severely impaired, and in some cases sufferers still show a covert emotional response to familiar faces, detectable by measuring (for example) skin conductance.

These results and others gained from studying the Capgras delusion have helped uncover the normal psychology of face recognition. The study of mental illness to uncover the normal function of the mind and brain is known as cognitive neuropsychiatry, and study of the Capgras delusion has been cited an early success in this field of study.

In fiction
Situations in which the protagonist (and the audience) knows that their acquaintances have been replaced by spies, aliens or monsters while the rest of the people think the protagonist insane appear in several works of horror and science-fiction. Well-known examples include Invasion of the Body Snatchers, The Stepford Wives, Total Recall and The Faculty.