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Old 11-24-2008, 12:06 PM   #999
alkemical
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Celebrity 'blindness' down to brain wiring

* 18:00 23 November 2008 by Ewen Callaway
* For similar stories, visit the The Human Brain Topic Guide

If you can't tell Angelina Jolie from Jennifer Aniston, total ignorance of pop culture might not be the only culprit. People with a rare condition called "face blindness" lack connections in a brain area responsible for recognising faces, new research shows.

Officially termed prosopagnosia, face blindness takes two forms: acquired and inherited. People who develop the condition later in life have usually suffered a stroke or an injury in a brain region important for facial recognition called the fusiform gyrus, says Cibu Thomas, a neuroscientist who led the study while at Carnegie Mellon University in Pittsburgh, Pennsylvania.

The inherited form – which may affect up to one out of 50 people – is far more mysterious. Tests of facial recognition can diagnose inherited prosopagnosiacs, but functional brain scans have revealed few differences between their brains and those of people who can pick out celebrities and loved ones.

"Here's a brain that looks normal in an MRI, and in some cases they have difficulty in recognising their own spouse," says Thomas, who is now at the Harvard Medical School.
Wiring differences

In search of a deeper cause, Thomas and his colleagues subjected six face-blind subjects to a type of brain imaging which reveals the structural connections that allow distant parts of the brain to communicate.

Called diffusion tensor imaging (DTI), the technique has revealed wiring differences in the brains of people with synaesthesia, compared to people without the condition.

The brains of prosopagnosiacs housed fewer connections than controls in two tracts that run smack through the fusiform gyrus; while other parts of their brains showed no such wiring differences, the team found.

Slower or noisier neuron signals to and from the fusiform gyrus could explain some cases of face blindness, Thomas says.
Face the test

On tests of celebrity face recognition – identifying a hairless Elvis Presley, for instance – these brain connections predicted the scores of people with prosopagnosia, as well as controls. This suggests that prosopagnosia is a matter of degree, Thomas says.

Test your own face blindness here

Thomas' team doesn't know what could cause these changes, but a German team has found that face blindness runs in families and is currently searching for genes linked to the condition.

This hunt might not be so clear cut, says Brad Duchaine, a cognitive neuroscientist at University College London.

Duchaine says the new findings offer a great explanation for some cases of prosopagnosia, but at least six brain regions are involved in face processing and various injuries or biological changes could affect how they work. "There are a lot of ways that face processing can go wrong," he says.

Journal reference: Nature Neuroscience (DOI: 10.1038/nn.2224)
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