The mystery of why some people never forget a face while others struggle to recognise people they have already met could be explained by two small bundles of nerves in the brain, according to a new study.
For the first time, scientists demonstrated that two clusters in a brain region called the fusiform gyrus play a central role in the way we see faces, but not other objects.
Tests on a patient with prosopagnosia – a condition where sufferers cannot distinguish one face from another – showed that electrical stimulation of the nerves instantly caused his perception of a face to become warped, while other objects in his field of vision remained unchanged.
Researchers said the findings could lead to new treatments for the condition, and may also explain why some people have a better memory for faces than others. Up to two per cent of the population are though to suffer from some form of "face blindness".
The experiment on Ron Blackwell, a 47-year-old father-of-two, made use of electrodes already implanted in his brain around the fusiform gyrus as part of a separate epilepsy treatment.
In a video accompanying the new study in the Journal of Neuroscience, Mr Blackwell describes how the researcher's face appears to completely change as a mild electric current is applied to his brain.
He says: "You just turned into somebody else. Your face metamorphosed.
"You look almost like somebody I've seen before, but somebody different ... you were someone else.
"It's almost like the shape of your facial features drooped."
When the electric current was halted, the researcher's face immediately returned to how it had initially appeared, he reported.
Prosopagnosia can affect patients from birth or arise as a result of brain damage in later life. Sufferers cannot tell the difference between one face and another, but the rest of their vision is completely normal.
Dr Josef Parvizi of Stanford University, who led the study, said the findings demonstrate that the two clusters, which are half an inch apart near the base of the brain, are critical to facial recognition.
Previous studies had indicated that the clusters were more active when people viewed pictures of faces compared with images of hands, legs or other objects, but the new study was the first to provide experimental proof.
