London, Nov 24 : Cannot tell Brad Pitt from George Clooney on the same magazine page? Well, you may be suffering from a rare condition called "face blindness", which scientists claim results from a lack of connections in a brain area responsible for recognising faces.
Called prosopagnosia, face blindness takes two forms: acquired and inherited.
Cibu Thomas, a neuroscientist who led the study while at Carnegie Mellon University in Pittsburgh, Pennsylvania, said that people who develop the condition later in life are usually those who have suffered a stroke or an injury in a brain region important for facial recognition, called the fusiform gyrus.
However, the inherited form of the disease, according to researchers, is far more mysterious and affects up to one out of 50 people. Facial recognition tests can detect prosopagnosiacs, but functional brain scans found some differences between the brains of people with and without the disease.
"Here's a brain that looks normal in an MRI, and in some cases they have difficulty in recognising their own spouse," New Scientist magazine quoted Thomas, who is presently at the Harvard Medical School, as saying.
For the study, the researchers made six face-blind subjects to undergo a type of brain imaging that could reveal the structural connections allowing distant parts of the brain to communicate.
The technique, called diffusion tensor imaging (DTI), uncovered wiring differences in the brains of people with synaesthesia, in comparison to people without the condition.
It was found that the brains of prosopagnosiacs had less connections than controls in two tracts that run smack through the fusiform gyrus. But there were no such wiring differences in other parts of their brains.
Thomas said that slower or noisier neuron signals to and from the fusiform gyrus could justify some cases of face blindness.
In celebrity face recognition tests, for example where subjects were asked to identify a hairless Elvis Presley, the brain connections predicted the scores of people with prosopagnosia, as well as controls.
Thus, Thomas deduced that prosopagnosia is a matter of degree.
Now, a German team has found that face blindness is hereditary and is currently searching for genes linked to the condition.
Brad Duchaine, a cognitive neuroscientist at University College London claimed that the hunt might not be so clear-cut.
Duchaine said the new findings may provide 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 said.