Prosopagnosia

__Overview __
Prosopagnisa is type of agnosia or inability to recognize faces. Those with this disorder are often considered “face blind” because they cannot recognize others on the basis of visual perception. Instead, other cues are utilized such as voice intonation, hair style and clothing.This disorder effects about 2% of the population and can be congenital but it is often acquired by severe head trauma. Its effects are precipitated by lesions of the fusiform gyrus ( medial temporal occipital gyrus) and can produce localized visual system deficits. In this wikispace, I will describe the symptoms of the disorder and also give background about the anatomical structures involved, effects on the visual system and common diagnostic tests.

__Symptoms __
 Prospagnosia is a disease that effects facial memory. Individuals with this condition are able to make non-facial visual discriminations and can often categorize visual stimuli as a face. However, if they are instructed to idenitify a person without the use of voices, clothing or specific attributes, they cannot identify a familiar person (Mayer and Rossion) or even themselves. A study done by Bukach and Caldara found that patients with the disease typically have difficulty recognizing the upper part of the face such as the eye region and instead utilize the mouth and other external aspects to identify faces.



__Overview of the Visual System __
The visual system is a complex organization of fibers that project from the retina to the visual cortex. Information about the external visual field is processed by rod and cone cells that connect to M (motion and spatial perception) type and P (form and color) type ganglion cells. They ultimately join to form the left and right optic nerves. When these fibers reach the optic chiasm they bifurcate; temporal retinal information remains ipsolateral, while nasal retinal information decussates and travels contralaterally.

Fibers then proceed to subcortical regions such as the lateral geniculate nucleus LGN of the thalamus and the superior colliculus. However, most fibers travel through the LGN and terminate in the magnocellular (location of P type cell termination) and parvocellular (location of M type cell termination) layers. The LGN then projects to the primary visual cortex (V1).The primary visual cortex (Brodmann Area 17) processes information by way of two different streams: the ventral stream and dorsal stream. The dorsal stream’s principle role is visually guided prehension without comprehension and the ventral stream is responsible for visual thought, planning and memory offline (Milner 2012).

__Visual Processing and Prospagnosia: __


Acquired prospagnosia involves lesions of the ventromedial regions of the occipitotemporal cortex which encompasses the following regions: the lingual fusiform, parahippocampal gyri, and more anterior aspects of the temporal lobes (Hoffman). These region are significant in prospagnosia because they participate in facial memory. Meadows’ research on The Anatomical Basis of Prospagnosia speaks about the effect of lesions on the visual system and highlights connections between lesions of the occipitotemporal cortex as having significant effects on the deep white matter; particularly the tapetal fibers from the corpus collosum, the inferior longitudinal fasiculus (ILF) and the optic radiations (Meadows). Effects of these lesions are manifested as contralateral quadrantic visual field defects. However, Meadows proposes that lesions of the occipitotemporal cortex are not the only way the disease presents, but that those within the ILF may cause similar symptoms.

__Congenital Prosopagnosia (CP) __
Individuals with congenital prospagnosia are born with an inability to recognize faces. This form is less common than acquired prosopagnosia (AP) and is not the result of brain damage. Mechanisms and symptoms of CP are not clear but an article by Behrmann and Avidan highlight different types of visual impairments that may be related to CP. They include the following: distingushing a face from non- face stimuli, determining whether two faces are the same or different and recognizing the individual identity of a face. The article also discusses the two different forms of prosopagnosia: apperceptive and associative. Apperceptive describes the lack of an intact perception while the an associative deficit is one of recognition and assessment of meaning. Insight into CP is significant as it allows for a greater understanding of the psychological and neural mechanisms of facial processing.

__Diagnosis __
The most common diagnostic tool is a matching test called the Benton face recognition test. Subjects are presented with several photographs one of which is called the “target photograph” (depicted in the photo above as A) which serves as the point of reference. Prosopagnostics are evaluated on the following matching tasks: matching a frontal view of the target with an identical photo, matching a frontal view of the target individual with three photos of the target taken from different angles and matching a frontal view taken of the target individual with three photos of the target taken under different lighting conditions (Duchaine). However, there has been some debate about the accuracy of this test because some prosopagnostics have been able to achieve normal scores.

__Conclusion __
There is currently no cure for prosopagnosia but individuals with this disorder are encouraged to practice facial recognition tricks. Prosopagnostics may have difficulty in social situations as they are not able to remember those they come in contact within unless these people have distinguished external features. Researchers are continuing to study this disease and are especially considering ways of understanding the mechanisms of congenital propagnosia. The video below gives great perspective on the severity of the disease. media type="youtube" key="vwCrxomPbtY" width="425" height="350" align="center"

__<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Glossary __
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Broadman Area 17- the primary visual cortex (striate cortex) is apart of the occipital cortex that receives information from the optic radiations.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Benton Face Test- diagnostic exam for prospagnosia that involves matching faces.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">tapetal fibers- fibers connected to the tapetum which is the layer of tissue immediately behing the retina.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">corpus collosum- nervous tissue that connects the two cerebral hemispheres allowing communication between right and left side of the brain.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">inferior longitudinal fasiculus (ILF)- fibers that allow for connection between the occipital and temporal lobes.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">acquired prosopagnosia (AP)- inability to recognize and remember faces due to brain injury.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">congenital prospagnosia (CP) - one born with an inability to recognize and remember faces.

__**<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">QUIZ **__
<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">1) T/F the posterior fusiform gyrus is involved in prosopagnosia

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">2) T/F congenital prosopagnosia is less common than acquired prosopagnosia

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">3) T/F lesions of the occipitotemporal cortex can produce ipsolateral visual system defects

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">4) T/F Broadmann area 17 is not a major player in the visual system

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">5) T/F visual system information crosses at the optic chiasm and goes directly to the primary visual cortex

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">6) Describe the difference between congenital prospagnosia and acquired prosopagnosia.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">7) What are the symptoms of prosopagnosia? Why is this disorder so difficult to deal with?

<span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">8) Describe the effect of prosopagnosia on visual processing.

Solutions to T/F. Solutions to 6-8 can be found within the wiki.

1) F

2) T

3) F

4) F

5)F __**REFERENCES**__

http://hsf.bgu.ac.il/avidan/TrendsinCog05.pdf

http://www.faceblind.org/social_perception/papers/duchaine03neuropsychologia.pdf

http://en.wikipedia.org/wiki/Prosopagnosia

http://www.nefy.ucl.ac.be/facecatlab/PDF/Mayer-Rossion07.pdf

http://web.mit.edu/bcs/nklab/media/pdfs/duchaine06CN.pdf

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3025660/- gives information on possible mechanisms of prosopagnosia

http://www.nefy.ucl.ac.be/facecatlab/resProject/Prosopagnosia.htm- great website to find links to other scholarly articles!

__**VIDEOS**__

http://www.nytimes.com/2011/12/27/health/views/face-and-voice-recognition-may-be-linked-in-the-brain-research-suggests.html?_r=3&hpw&

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http://jn.physiology.org/content/93/1/603.full