Delusions are a marker of scientific advancement. In one era, a given delusion is considered a case of demonic possession. In another era, the same delusion is considered generically as the result of generalized insanity or dementia. And in another, more recent era, the same delusion is linked to a specific brain injury or genetic etiology.
This progressively more precise and thorough understanding of what a delusion is parallels many other neuroscientific advancements, but is also distinct because of its visibility. We can “see” delusions play out in others, and be described in literature, depicted in movies, and discussed as a standard part of our cultural vernacular.
One such delusion is Capgras’ Syndrome (aka ‘Phantom Doubles Syndrome’), in which the sufferer believes a family member or friend has been replaced by an impostor who has the exact characteristics of the original. Worse still, the sufferer may believe him/herself to be the impostor. But this goes even beyond believing someone to be an impostor — a person with Capgras’ Syndrome sees an impostor, which affirms and strengthens the belief. When the impostor is oneself, a person with Capgras’ Syndrome may remove all mirrors in their house to avoid seeing a doppelganger looking back.
Courtesy of PsychNET, these are a few of the delusion’s characteristics:
The person is convinced that one or several persons known by the sufferer have been replaced by a double, an identical looking impostor.
The patient sees true and double persons.
It may extend to animals and objects.
The person is conscious of the abnormality of these perceptions. There is no hallucination.
The double is usually a key figure for the person at the time of onset of symptoms. If married, always the husband or wife accordingly.
The causes of the delusion are not entirely clear or agreed upon, but some linkages have been established.
It has been reported that 35% of Capgras’ Syndrome and related substitution delusions have an organic etiology. Some researchers believe that Capgras’ syndrome can be blamed on a relatively simple failure of normal recognition processes following brain damage from a stroke, drug overdose, or some other cause. This disorder can also follow after accidents that cause damage to the right side of the brain. Therefore, controversies exist about the etiology of Capgras’ Syndrome; some researchers explain it with organic factors, others with psychodynamic factors, or a combination of the two.
The video below is a clip from the BBC show “Phantoms in the Brain” in which V.S. Ramachandran discusses Capras’ Syndrome and two other types of delusional disorders, particularly in light of what is known about the brain’s visual processing system. It’s roughly 10 minutes long and is part two of five; all parts are available on YouTube.