There is a short piece in the Science Times this morning about a rare form of the already rare Capgras syndrome, in which someone can no longer recognize certain people who are close to them, believing them to be imposters. The piece, which I link to here, is surprisingly uninformative, giving a psychoanalytic explanation for the condition which considers it a form of displacement, which is in a sense not arguable, but, while it mentionins that there may be a neurological cause, it never discusses the credible theories that exist. So I will.
I also found it surprising that the article made no reference to The Echo Maker, a fantastic novel by Richard Powers that came out less than a year ago and received tons of press. It may indeed be the source of your own familiarity with Capgras, if you've read it, as its plot revolves around a man, Mark, who acquires the syndrome following a car accident and can no longer recognize his sister or his dog. A little primer here on our best understanding of the neuroscience behind face recognition both when it works and when it breaks down.
The human face - it's the chief tool we use to determine the identity of others - although there are other cues. Given the fact that the same basic features comprise most faces and sit in relatively the same place, it is a wonder how we make distinctions among thousands of faces every day and can usually recognize a person as familiar somehow after a single meeting (even if we're struggling for their name). Aside from the normal visual apparatus that we use to see and identify any object at all, a network of regions that include the fusiform face area and the occipital face area have been identified as responding more strongly to faces than to other objects and are probably involved in face detection and perception (although probably not as much in gaze perception, head detection, or memory for faces). Some scientists persuasively argue that the fusiform face area specializes not for faces per se, but rather for objects for which we have great expertise and that faces are simply the exemplar of something requiring this kind of processing, but I won't get into that argument now.
Prosopagnosia is a deficit in which people cannot recognize faces. Even though prosopagnosics cannot overtly recognize people from their faces, their body tells us by other means (measures of perspiration a change in the autonomic nervous system that indicates emotional arousal, ) that are though to be a form of covert recognition - some part of us recognizes the familiar face even if we do not consciously register it. It has been suggested that there are two concurrent visual pathways, a ventral one is providing the detection of identity by matching the stimuli we are seeing with something in our memory, while a dorsal route is providing emotional information that distinguishes what is relevant to us from what is irrelevant by involving the limbic system (associated with emotions), and providing a source for this covert recognition - an unconscious feeling of familiarity.
Capgras syndrome is a delusion that someone closely related to the patient and recognized as resembling that person has been replaced by an imposter. Misidentification syndromes are not exclusive to human stimuli, they can involve inanimate objects as well. While the precise location of the pathology is not yet identified, it has been shown that Capgras patients recognize the the faces - i.e. their form a match with information in their memory - but do not show the emotional or covert response, that sends the message indicating familiarity. So Capgras is effectively the mirror image of prosopagnosia. If the two route model holds true, Capgras is explained as damage to the dorsal route connection the limbic system. However, this creates an interesting paradox - the emotional response is assumed to demonstrate the relevance conferred on the face by its familiarity, however, the stimuli has to have been recognized already as familiar before it can elicit this emotion. So a newer model suggests one route until recognition with two pathways afterward - one to biographical information and the second to emotion information. In either case, it is damage to the limbic system and or the connection to it that is presumed to be at fault and researchers interested in such subjects have been exploring damage to the amygdala - an important component of the limbic system - as a player in Capgras syndrome.
I find it troubling that all of these models omit any discussion of the delusional component of Capgras in which lack of a confirmatory feeling is given an absurd rather than a reasonable explanation. If a friend who I've haven't seen without long sideburns for the last five years walks into the room with them shaved off, I may feel that there is something different about him but be unable to place what it is for a while. However, I am unlikely, even at my worst moments, to think that he is an alien from outer space who has replaced my friend. That is usually the type of delusion you hear about with Capgras. Some neuroscientists expect that there is concurrent frontal lobe damage. Others are looking for two anatomical sources for the covert recognition as opposed to one. The jury is out.
Today's Science Times article, written by a psychiatrist says:
My patient suffered from a variation of Capgras syndrome, in which people are replaced by inexact duplicates. It has been considered rare, but the more I work with geriatric patients, the more I am diagnosing it.
I found this the most interesting part of the article. I'm curious whether this "inexact" duplication suggests a subclass of Capgras patients that have damage to both the overt and covert types of recognition or whether it is simply a variation in the narrative that accompanies their particular delusion.
Richard Power's novel The Echo Maker gives both beautiful and credible expression to what it must be like to be inside such a delusion. It also deals meaningfully with the repercussions that are experienced by his sister Karin, who uproots herself to help her brother in his crisis, and a famous neurologist who visits him and who I took to be a fictional amalgam of the neurologist and writer Oliver Sachs and the neuroscientist and theorist in consciousness Gerald Edelman. It is mysterious to contemplate identity - one of my favorite subjects - we would all likely say we have one (or at least one) but where does it originate? Is it fixed or malleable? What does it mean not to be recognized - not from one's physical appearance but because one doesn't seem the same anymore. Karin is understandably distressed because Mark doesn't think she is the same person anymore, and yet her brother goes through a terrible accident and she leaves her job and her life to care for him - OF COURSE SHE IS NOT THE SAME PERSON ANY MORE! Mark is undeniably delusional as Karin knows she is Karin and has not been replaced by the government, but there is a peculiar truth to his perception that she is no longer the same, which is expressed in all its complexity by Powers novel as Karin deals with the day-to-day realities of Mark's accident. The doctor too observes the nature of his own identity in light of experiencing the fragility of who we are through Mark's disease. What Power's novel expresses so well about Capgras (which is not its only point by a long shot) is that the syndrome cannot be said to be exclusively neurological any more than it can said to be psychological. In this day and age, one does not exist without the other.