The Capgras Delusion

In March 1895, a cooper lived in a small Irish town with his wife and her father. Their house was built on the site of a fairy ring fort. After growing suspicious that there were witches roaming around, the cooper became convinced, along with his father-in-law, that his then-ill wife was possessed by a changeling and that she looked like, but was not, his wife. As superstitious beliefs had it at the time, the only way to bring his wife back was to burn the changeling out of her. He gathered at home with eight neighbors and they collectively set the woman on fire. Some of the details of that story were invariably altered by time and rumor, but the homicide of Bridget Cleary by her husband in 19th-century Ireland is undeniably true.

A few decades later, the Capgras delusion was reported in 1923, when Jean-Marie Joseph Capgras and his intern Jean Reboul-Lachaux described the case of a 53-year-old woman who believed that her husband, her children, the police, and her neighbors all had been replaced by identical-looking imposters (Capgras & Reboul-Lachaux, 1923). Long thought to be a psychiatric phenomenon with no neurological basis, the Capgras delusion has increasingly come to be seen as originating from a brain disorder with increasing evidence for its occurrence after head trauma or stroke, and in neurodegenerative illnesses (Alexander, Stuss, & Benson, 1979; Collins, Hawthorne, Gribbin, & Jacobson, 1990; Gluckman, 1968; Goldfarb & Weiner, 1977; Horikawa et al., 2006; Merrin & Silberfarb, 1976; Weston & Whitlock, 1971). Misidentification syndromes were found to occur in 15.8% of AD and 16.6% of clinically defined patients with dementia with Lewy body, of which the Capgras delusion is the most common (Harciarek & Kertesz, 2008).

Many neuropsychological theories are proposed to explain the phenomenon of Capgras delusions. Staton, Brumback, and Wilson (1982) described the case of a patient with a right posterior hippocampus and right temporoparietal–occipital junction lesion resulting in the Capgras delusion as well as reduplicative paramnesia, the delusion that a place has been doubled and exists in two places. They postulated that the syndrome occurred as the result of a disconnection between remote memory stores and new memory formation. Unable to lay down new memories of subtle changes in physical appearance, the subject relies on stored images from the past to process present visual cues; the illusion of doubles is created. However, this theory accounts for neither the laterality of the lesion nor the specificity of Capgras delusion to attached faces. In addition, an unpublished series of three patients with Capgras delusion failed to demonstrate a clear temporal cutoff when patients were presented with backdated pictures of their misidentified relative (Edelstyn & Oyebode, 1999).

Other proposed neurological theories include a disconnect between two brain hemispheres, each generating its own image of a known face (David, 1994; Edelstyn et al., 1997; Joseph, 1986); a malfunction of the right hemisphere, thought to be specialized in the “recognition of uniqueness” (Cutting, 1990; Kosslyn, 1987); and a disconnection between “overt” and “covert” face visual-processing pathways (Bauer, 1984; Ellis & Young, 1990; Ellis et al., 1997). According to the latter theory, the Capgras delusion may behave as the “mirror image of prosopagnosia,” defined as a general inability to recognize faces. In fact, patients with prosopagnosia retain the appropriate skin conductance response expected when looking at familiar faces (Bauer, 1984); the opposite is true of patients with the Capgras delusion (Ellis et al., 1997; Hirstein & Ramachandran, 1997). Bauer (1986, 1984) described a dual pathway of face processing: overt and a covert, or affective, recognition. While he entertained the idea that prosopagnosia results from damage to the overt route with preservation of the covert route, Ellis and Young (1990) proposed that the opposite results in the Capgras delusion.

However, as Hirstein and Ramachandran (1997) point out, this theory has a few fallacies, notably that lesions resulting in the Capgras delusion are more commonly ventral (occipitotemporal) and that the ventral pathway is strongly connected with the amygdala. Ramachandran proposes that the delusion results from a disconnection between face-processing areas and the limbic system. This leads to the creation of separate memory “files” of the same person, because patients fail to link together successive episodic memories. Most lesions studies point to a dysfunction in the right hemisphere with a possible predilection for lesions in the right temporo-parieto-occipital region, which suggests that a dysfunction of face processing with possible limbic dysfunction could underlie the Capgras phenomenon. Infarction in the right hemisphere was also found to be implicated in patients with Cotard delusion, the belief that one is not alive (Nishio & Mori, 2012).

Regardless of their validity, these theories explain neither the specificity of the Capgras delusion to closely loved ones nor the formation of a fixed belief that is not amenable to change when provided with evidence to the contrary. Other caveats to theories of visual face processing in the misidentification of loved ones are reports of the Capgras delusion in blind patients (Dalgalarrondo, Fujisawa, & Banzato, 2002; Hermanowicz, 2002; Rojo, Caballero, Iruela, & Baca, 1991) and cases in which it manifests over the phone in the absence of the visual stimulus of the loved one's face (Dietl, Herr, Brunner, & Friess, 2003). It might be that Capgras delusion finds its neurophysiology at a larger scale than a simplistic visual face-processing dysfunction or that these cases are physiologically distinct with a seemingly common phenotype.