Capgras syndrome is one in which a patient has a delusional belief that a person or persons, usually well known to them, have been replaced by an identical impostor(s). It usually occurs in the context of a psychotic illness (more than half of cases are associated with schizophrenia) but may be seen with other psychiatric illnesses, including brain injury or dementia.
The Capgras delusion is one of a number of delusional misidentification syndromes, a class of delusional beliefs that involves the misidentification of people, places or objects.
Joseph Capgras (1873-1950) was a French psychiatrist who first described the disorder in a 1923 paper co-authored with Reboul-Lachaux about the case of a French woman who complained that various ‘doubles’ had taken the place of people she knew. They called this ‘L’illusion des sosies’ (the illusion of doubles).
Current thinking as to the cause of Capgras syndrome has focused on dysfunction of the inferior temporal cortex and the amydala. The former is involved with recognising faces and the latter with the simultaneous emotional reaction. These two structures can be damaged independently; if the ability to recognise faces remains intact but the emotional reaction which makes them familiar is absent, it is hypothesised that the conculsion drawn will be that the person in question is an identical impostor.
Uncommon psychiatric syndromes – Enoch, Enoch and Ball – is an interesting book with chapters on this syndrome and others. I read it on holiday in Syria, which I think shows true dedication to my cause.
nb: if anyone has a view on whether it’s ‘Capgras’ syndrome’ or ‘Capgras syndrome’ then I’d be pleased to hear it.