Capgras' Syndrome is a delusional disorder in which the victim believes that all of his close friends and family members have been replaced with nearly-exact replicas, often perceived as robots or actors. Cotard's Syndrome involves believing yourself to be dead, that you no longer exist, and (sometimes) that your limbs and body belong to another. These two disorders do not deserve separate writeups because they are caused by damage to the same part of the right hemisphere of the cerebral cortex, and are thus just different cognitive interpretations of the same perception. Cotard's is always accompanied by severe depression, while Capgras' is not, in most cases.

These diseases are caused by a breakdown -- which can be caused by accident, stroke, etc. -- in the pathway between perception and affect. That is to say, while the victim can tell who someone is, they receive no emotional response from the recognition. For instance, you might visit your mother and recognize her completely, but it wouldn't feel like what being with mother was actually like. A Capgras sufferer would interpret this as being because his mother was an imposter, while a Cotard sufferer would assume that he had no response because he was dead inside. A theory suggested for the differences of these interpretations is that the depression accompanying Cotard's caused the victim to view the perception change as being his fault for being dead, while the non-depressed Capgras sufferer sees the difference in actions that others suddenly started doing wrong.

These syndromes are the exact opposite of prosopagnosia, where the visual/recognition pathway is broken but the emotional one is not, making it impossible to recognize the face of a loved one while still allowing emotional response to their name.

Treatment with the bicyclic and tricyclic antidepressives has no effect on the delusions, although it may break the Cotard's sufferer's depression. Electroconvulsive therapy, however, has been shown to improve blood flow to the damaged areas, in many cases ending the delusions after only a few treatments. If the brain area has been completely destroyed, severed by an automobile accident or what have you, recovery is impossible and the delusions will probably last for the victim's entire life.

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