Notes on Congenital Prosopagnosia

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Congenital Prosopagnosia:

• FOXP2 mutation.

• Autosomal Dominant.

Principles

• Founder Effects.

• Point mutation.

• Monogenic disorder.

• Variable expressivity.

Major Features

• Inability to recognize and remember faces – “face blindness.”

• Age of onset: Infancy through adulthood.

• Patient is socially isolated.

History

First reported in the 19th century by Hughlings Jackson and Charot, the term “prosopagnosia” was coined in 1947 by Joachim Bodamer from Germany. Also known as “face blindness”, and originally thought to be caused by trauma to the brain before or after birth, a new study finds that another version of prosopagnosia exists; and this one is caused purely by genetic factors. As reported by German researchers in the American Journal of Medical Genetics, another version of this disease involves a certain deletion or mutation in the FOX2 gene. Furthermore, this disorder is highly common and affects 1 in 50 people – that is 5 million people in the U.S. alone. One patient reports offending many friends simply by ignoring them in public places. She also reported not recognizing her mother’s face, her own face in school book pictures, and the faces of her children.

Most prosopagnosics become used to the disorder early in life, and develop various ways to overcome their forgetfulness. Instead of looking at the face, they try to recognize people by other factors like personal odor, voice, hairstyle, gait and overall shape of body. They even avoid places that are commonly visited by their friends and family so as to not run into them. They may even pretend to be lost in thought or looking elsewhere while walking down a street. Some try to be friendly to everyone they see. Thus, these people are basically hiding their disorder from public – and this is one of the reasons why prosopagnosia went undiscovered for such a long time until now. To study how common the disorder is, researchers picked and interviewed 689 random students from local colleges and found that prosopagnosia existed in 17 first degree relatives – corresponding to a prevalence of 2.47%. On further investigation with the students’ families, more prosopagnosics were discovered. The researches stated that here is proof that the disease is more common yet concealed than originally thought.

Causes

This disease is thought to be caused by a defect in the temporal or occipital lobe of the brain – both of these are fully used in face reorganization. Unfortunately, only a small number of neural studies have been done on this disorder. There are two, however, involving the evoked response potentials (ERP) that study the N170 potential recorded from the temporal lobe. The N170 potential is elicited whenever the brain encounters familiar objects such as tables, chairs, cars, etc. In normal people, the N170 response is the same for all objects including faces. In prosopagnosics, however, the N170 response in terms of amplitude gets weaker when faces are encountered – but the same for all other objects. In another study, a magnetic resonance and imaging showed a similar response in prosopagnosic individuals in the fusiform face area (FFA). There may be more factors involved, and more research is being done on this relatively new disorder.

Findings

There are no physical phenotypes – affected individuals appear perfectly healthy. Individuals affected by this highly common but least reported disease cannot recognize faces of friends, family, and even themselves in front of crowded mirrors. This causes patients to be socially reclined and even avoidant of public places so as to avoid meeting familiar people and “ignoring” them. There also exists great variability among the group of sufferers. Generally, the common ground among all prosopagnosics is that they can see facial features clearly, but cannot recognize these features if seeing them again. Mild prosopagnosics may train themselves to remember a limited number of faces, while those severely affected may not identify their own. To make things worse, sufferers are judged as uncaring and ignorant by the general public – and this may cause depression in some.

Additional studies have been done on prosopagnosics taking into account various variables like time required to match individual facial features, reaction time, more detailed facial features (age, gender, etc.) and the like. It has been found that almost 50% of the patients can discern age and gender, and the remaining half cannot. The same statistics go for recognizing emotional expressions. These tests were repeated with famous faces with more or less the same results. Whether or not the same brain machinery is used to recognize both faces and objects is being hotly debated within the neuroscience community. Studies done in monkeys suggest that faces are handled separately by the brain. Research using MRI shows that there is a general purpose area in the brain that handles both these visual needs. Some researchers argue that both the processes are true. Adding to the complexity, some of these processes apply to some patients, and some apply to others. Further research is being conducted in this area.

Updates

According to recent studies, a different kind of neural processing is required for the brain to process faces – configural processing. Research shows that a mutation in configural processing area of the brain may cause prosopagnosia. This view comes from research done on patients with lesions of the fusiform face area in the brain. These patients have a difficult time deriving the spatial relations between the components of the face – that is – they cannot remember the distances between the eyes and the nose and the lips – having a generalized view that all faces look alike. This fact has also been proven by studies comparing processing of inverted versus upright faces. In normal people, processing and remembering upright faces is easier than remembering inverted faces. This is true because upright faces are processed as a whole as opposed to a part based system used when faces are inverted. This holds true because we can clearly remember human faces as opposed to faces of, let’s say, monkeys. In prosopagnosics, however, it doesn’t matter whether the face is upright or inverted. In fact, some prosopagnosia have performed better when the faces were inverted. This is because these individuals are reading faces based on facial features, not as whole objects as normal people do – and this is the basic principle of configural processing.

Conclusion/Inheritance Risk/Disease Management

This is an autosomal dominant disorder – if one parent has it, there is a 50% chance of a child having it. The study of prosopagnosicia has led us to deeper understanding of the neural and psychological mechanisms used to process faces and how all this is related to non-face processing non-face objects. There is currently no treatment for congenital prosopagnosicia.

There are many open-ended questions like: In addition to impaired face recognition, what other features are impaired? Are there more genes involved? Exactly what brain functions are involved? How can face recognition be improved in prosopagnosics?

References

http://en.wikipedia.org/wiki/Prosopagnosia (accessed August 2)
http://www.faceblind.org (accessed August 2)
http://www.ninds.nih.gov/disorders (accessed August 2)
http://www.gnxp.com/blog (accessed August 2)
Time Magazine - July 17th 2006
Behrmann, M. and Avidan, G. (2005) Congenital prosopagnosia: face-blind from birth. TRENDS in Cognitive Sciences Vol.9 No.4
[PDF: www.univie.ac.at/mcogneu/lit/behrmann.pdf] (accessed August 2)

Additional Reading:

Basic Neurology

1. Peripheral Nervous System
2. Central Nervous System
3. The Ventricular System
4. The Spinal Cord
5. The Brain Stem
6. The Cerebellum
7. Visual Pathways
8. Diencephalon
9. Basal Ganglia
10. Cerebral Cortex
11. Sleep Disorders
12. Autonomic Nervous System
13. Cranial Nerves and Parasympathetic Ganglia
14. Cells of the Nervous System
15. Cerebrospinal fluid
16. Additional short notes on Cerebrum
17. Functions and Diseases of Cerebrum
18. Subcortical Grey Matter
19. Notes on The Spinal Cord
20. Regulation of Heart Rate by Autonomic Nervous System
21. Action Potentials, Axon Conduction, and Neuromuscular Junction
22. Types of Seizures
23. What is a Cough Reflex?
24. Notes on Congenital Prosopagnosia
25. Findings in Parkinson's Disease
26. Types of Heat Strokes
27. Types of Strokes
28. What is Benign Intracranial Hypertension?
29. What is Cauda Equina Syndrome?
30. Cranial Nerve Locations in Brain Stem

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