Some of you might find the following article to be of interest. Jeff ---------------------------------------- http://www.dallasnews.com/science/columnists/346200_tomcol_23liv.html Scientists learn how familiarity breeds delusion 04/23/2001 By TOM SIEGFRIED / The Dallas Morning News The next time the Earth is invaded by pod people, it might be a good idea to call a psychiatrist. Sure, your spouse and neighbors may be acting strangely because aliens have taken over their bodies. But it's also possible that you may be suffering from an obscure psychiatric disorder known as Capgras delusion. Victims of this delusion, say psychologists Hadyn Ellis and Michael Lewis, are seized by "the firm and sometimes dangerous belief that some people are no longer who they were: Instead they have been replaced by doubles, impostors, robots, aliens and so forth." First recognized more than a century ago in Germany, Capgras delusion takes its name from a French doctor who studied the notorious Madame M. in the 1920s. She insisted that her husband, children and neighbors had all been replaced by doubles. And then she believed that the doubles were replaced, as well. After a while she was on husband No. 80. Mme M. had other symptoms of mental illness, and Capgras sometimes occurs in schizophrenia and other psychotic disorders. But it can also be caused by brain damage. In one recent case in Wales, a man injured in a car crash contended that his wife had been killed and then replaced. Sometimes, the "impostor" may be a favorite tool or pet. In most cases, though, the victim believes that some emotionally close person has been replaced by a doppelgänger of some sort, possibly an evil twin. In any event, even though the replacement looks the same, it doesn't "feel" the same ? the way that Alec Baldwin could tell something was wrong with Meg Ryan in Prelude to a Kiss. Sometimes the delusion is so strong that the victim begins plotting to kill the "impostor." Capgras delusion could provide a clever twist for the next remake of Invasion of the Body Snatchers, but that's not why scientists are interested. When something in the brain goes so wrong, it's an opportunity to find out how the brain works normally ? in this case, in recognizing familiar faces. "Capgras delusion ... can provide us with a fascinating clue as to the very nature of normal face recognition," Drs. Ellis and Lewis write in the current issue of Trends in Cognitive Sciences. Right away, the delusion suggests that recognizing someone's identity involves more than one brain process. "Patients with Capgras delusion simultaneously recognize a face and, at the same time, deny its authenticity," note Drs. Ellis and Lewis, of Cardiff University in Wales. Therefore the normal brain must use one method for recognizing that a face is familiar and another for attaching an identity to it. Further clues come from another odd disorder, known as prosopagnosia, in which patients do not recognize familiar faces at all. (Victims of this disorder can, however, recognize familiar voices.) Prosopagnosia patients have no conscious recognition of familiar faces. But even while denying that a face is familiar, the patient's skin sweat increases just as when seeing familiar people. So it seems that the brain uses both a conscious and unconscious system for recognition. The conscious system decides whether the face looks like somebody familiar; the unconscious system confirms that the familiar face really does belong to the person it's supposed to. If that view is correct, the conscious system is damaged in prosopagnosia while the unconscious system is intact. In Capgras delusion, the problem is the opposite. The conscious system works, but no confirmation comes from the unconscious system. And recent studies show that skin sweat levels do not change for familiar faces in Capgras patients. Piecing together all this evidence, brain scientists have proposed that recognition involves two nerve pathways in the brain ? a lower path for recognizing familiarity in a face, and an upper path for assessing the face's significance. Capgras delusion disrupts the upper path. Of course, as Drs. Ellis and Lewis point out, it can't be all that simple. Even if the upper path does not confirm a face's identity, why is the result the delusion of a double? There must be some third part of the brain that is also disrupted ? whatever part compares the results of the two other processing paths. Some studies do suggest that there are different aspects of unconscious recognition involved in assessing faces. Some parts of the unconscious system do work right in Capgras, but others don't. Somehow the brain has to put all that information together correctly. If it doesn't, then delusions may result when the brain tries to create an explanation for why the pieces of the picture don't mesh. In any case, the study of Capgras delusion makes it clear that recognizing faces is not a simple mental process. "It is no longer possible to interpret face recognition as proceeding in a strictly sequential fashion along a single route," Drs. Ellis and Lewis write. And awareness of Capgras might also suggest reinterpretations of some classic sci-fi mysteries. Of course, knowing about Capgras would be no help at all if the body snatchers really did turn out to be aliens. Online at: http://www.dallasnews.com/science/columnists/346200_tomcol_23liv.html © 2001 DallasNews.com -- Jeffry P. Ricker, Ph.D. Office Phone: (480) 423-6213 9000 E. Chaparral Rd. FAX Number: (480) 423-6298 Psychology Department [EMAIL PROTECTED] Scottsdale Community College Scottsdale, AZ 85256-2626 Listowner: Psychologists Educating Students to Think Skeptically (PESTS) http://www.sc.maricopa.edu/sbscience/pests/index.html
