Thursday, March 29, 2012

The Bizarre Brain.

Prosopagnosia is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. The term originally referred to a condition following acute brain damage, but a congenital form of the disorder has been proposed, which may be inherited by about 2.5% of the population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus.
Few successful therapies have so far been developed for affected people, although individuals often learn to use 'piecemeal' or 'feature by feature' recognition strategies. This may involve secondary clues such as clothing, gait, hair color, body shape, and voice. Because the face seems to function as an important identifying feature in memory, it can also be difficult for people with this condition to keep track of information about people, and socialize normally with others.

The Capgras Syndrome
The Capgras delusion theory (or Capgras syndrome) is a disorder in which a person holds a delusion that a friend, spouse, parent, or other close family member has been replaced by an identical-looking impostor. The Capgras delusion is classified as a delusional misidentification syndrome, a class of delusional beliefs that involves the misidentification of people, places, or objects. It can occur in acute, transient, or chronic forms. Cases in which patients hold the belief that time has been "warped" or "substituted" have also been reported.

Many researchers think that Capgras syndrome is actually the result of something wrong with the brain, an organic cause. They look for lesions on the brain, signs of atrophy and other cerebral dysfunction. Although Capgras syndrome is usually seen in people who have psychotic disorders, more than a third of Capgras patients have signs of head trauma [source: Hirstein and Ramachandran]. Many Capgras patients also have other organic conditions, like epilepsy or Alzheimer's.
Still more doctors and researchers combine the idea of both a physical and a cognitive cause. There's something wrong with the brain, but why and how is Capgras syndrome occurring because of it? Maybe the organic cause leads to feelings of disconnectedness that lead to Capgras syndrome. Maybe it's too tough for people with a brain lesion to update memories when they see a person and the person looks slightly different. Your body is having a strange experience and your brain scrambles for a way to explain it.
Somewhere, the brain isn't communicating when it should be. This breakdown of communication might be happening between the part of the brain that processes the visual information for faces and the part that controls the limbic system's emotional response.
The argument seems to come down to whether Capgras syndrome is a problem of perception or of some other process, like memory. Hirstein and Ramachandran proposed that Capgras syndrome is a problem of "memory management." They give this example: Think of a computer. You make a new file and save it. When you want that information, you open the old file, add to it, save and close it again. Perhaps people with Capgras keep creating new files instead of accessing the old one, so that when you leave the room and re-enter, you are a new person, a person who looks like the one who left, but slightly different -- maybe your ears look bigger, or your hair a different hue. There's still a lot that science doesn't know about the human memory.
Some studies have also shown blind people with Capgras syndrome -- their delusion extends to the voice of a person, thinking that the voice is a voice of an impostor, instead of the face, so perhaps it isn't a face-processing problem at all. Other studies have shown people who were convinced by looking at a person that that person was an impostor, but they recognized the person's voice on the phone.

Fregoli Syndrome
The Fregoli delusion or the delusion of doubles is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise. The syndrome may be related to a brain lesion, and is often of a paranoid nature with the delusional person believing themselves persecuted by the person they believe is in disguise.
A person with the Fregoli delusion can also inaccurately replicate places, objects, and events. This disorder can be explained by "associative nodes." The associative nodes serve as a biological link of information about other people with a particular familiar face (to the patient). This means that any face that is similar to a recognizable face to the patient, the patient will recall that face as the person they know.
The condition is named after the Italian actor Leopoldo Fregoli who was renowned for his ability to make quick changes of appearance during his stage act.
P. Courbon and G. Fail first reported the condition in a 1927 paper (Syndrome d’illusion de Frégoli et schizophrénie). They described a 27-year-old woman living in London who believed she was being persecuted by two actors she often saw at the theatre. She believed these people pursued her closely, taking the form of people she knew or met.

Thatcher Effect
The Thatcher effect or Thatcher illusion is a phenomenon where it becomes difficult to detect local feature changes in an upside down face, despite identical changes being obvious in an upright face. It is named after British former Prime Minister Margaret Thatcher on whose photograph the effect has been most famously demonstrated. This was originally created by Peter Thompson, (Thompson, 1980).
The effect is illustrated by two originally identical photos, which are inverted. The second picture is obviously altered so that the eyes and mouth are vertically flipped, though the changes are not immediately obvious until the image is viewed in normal orientation.
This is thought to be due to specific psychological processes involved in face perception which are tuned especially to upright faces. Faces seem unique despite the fact that they are very similar. It has been hypothesised that we develop specific processes to differentiate between faces that rely as much on the configuration (the structural relationship between individual features on the face) as the details of individual face features, such as the eyes, nose and mouth. When a face is upside down, the configural processing cannot take place, and so minor differences are more difficult to detect.
This effect is not present in people who have some forms of prosopagnosia, a disorder where face processing is impaired, usually acquired after brain injury or illness. This suggests that their specific brain injury may damage the process that analyses facial structures.
Rhesus monkeys also show the Thatcher effect (Adachi, et al., 2009), raising the possibility that some brain mechanisms involved in processing faces may have evolved in a common ancestor 30+ million years ago.
(I found the pictures related to these rather grotesque, so I decided against including them in the blog)

This is my 100th blog post! Here's to a 100 more hundreds! :D Or maybe a Googol more posts!