The mirrored-self misidentification delusion

ISSN 1758-2008 10.2217/NPY.11.55 © 2011 Future Medicine Ltd Neuropsychiatry (2011) 1(6), 521–523 *Centre for Cognition & its Disorders, Macquarie University, Sydney NSW 2109, Australia; [email protected] The mirrored-self misidentification delusion is the belief that, when you look into a mirror, the person you see in the mirror is not yourself, but some stranger who happens to look like you. It is an example of a monothematic delusion (i.e., a delusion in which there is only a single abnormal belief present, or at most a cluster of abnormal beliefs related to a single theme). This contrasts with polythematic delusions, where a variety of unrelated delusional beliefs are present; for example, the mathematician John Nash believed during his schizophrenic episodes that he would become Emperor of Antarctica, that he was the left foot of God on Earth and that his name was really Johann von Nassau [1]. Other examples of monothematic delusions include Capgras delusion (the belief that someone emotionally close, such as a spouse, has been replaced by a stranger of the same appearance), Fregoli delusion (“People I know are following me around but I cannot recognize who they are because they are always disguised”), Cotard delusion (“I am dead”), somatoparaphrenia (“This arm [the patient’s own arm] is not mine, it is yours”) and the delusion of alien control (“Other people can cause parts of my body to move without my willing such movements”). How might such delusions be explained? What causes them? A promising approach here is the two-factor theory of delusional belief [2–4]. According to this theory, all that is needed for understanding any of the forms of monothematic delusional belief is to discover the answer to two questions. The first question is: what prompted the delusional idea in the first place? The second question is: what caused this idea to become an accepted belief, rather than it being rejected on the grounds of implausibility or bizarreness, or because the patient’s family and friends and clinicians are all insisting that the belief is false? Some success has been achieved in obtaining answers to these two questions for each of the monothematic delusions described above (for recent review, see Coltheart et al. [2]). For each delusion, it is possible to identify or plausibly hypothesize a neuropsychological abnormality responsible for the specific content of the delusional “It appears that the mirrored-self misidentification delusion is not uncommon in cases of dementia, but generally emerges only at so late a stage of the disease that it is too difficult to study in such cases.” Editorial