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Do I know you?

In brief

Do I know you?

Experiment pinpoints brain area linked to face blindness

What’s up with those rude characters you see coming down the hall every single day who never acknowledge your presence? Just as you get near enough for the standard, semiconscious exchange of glances that (for you, anyway) invariably leads to saying hello — they avert their eyes and walk past you as if you’re a perfect stranger.

It’s doubtful that they’re all suffering from out-and-out prosopagnosia, or face blindness, although as many as one in 40 people may have inherited some degree of it. (Famed author/scientist Oliver Sacks, MD, suffers from a congenital case.) But there’s no question that we differ in our ability to recognize faces. And that may have a lot to do with how things are going in a small, hand-rolled-cigarette-shaped brain structure called the fusiform gyrus that dwells at the bottom of each of our two temporal lobes, according to a recent Journal of Neuroscience study by Stanford neurologist Josef Parvizi, MD, PhD.

Stanford neuropsychologist Kalanit Grill-Spector, PhD, has been studying the fusiform gyrus’ role in face recognition as well as in prosopagnosia. People with prosopagnosia simply cannot distinguish one face from another, although all other aspects of their vision and visual-information processing are normal. Some people, like Sacks, are born with the condition while others acquire it as a result of an injury to the fusiform gyrus, Grill-Spector says.

“We can learn a lot about the function of different brain regions by studying these disorders and relating them to the anatomical sites where brain damage has occurred,” she says. “But the injuries vary a great deal from one affected person to the next, and they are typically not confined to the fusiform gyrus. This limits our ability to localize a particular deficit to a particular brain site.”

But Parvizi, collaborating with Grill-Spector, has nailed it in a striking experiment made possible because of a courageous epilepsy patient named Ron Blackwell.

Blackwell, who’d had part of his skull temporarily removed so that electrodes could be placed at the surface of his brain to monitor his seizures, decided that while he was lying there more or less immobilized for a week, he might as well pass the time doing something for science. So, working with Blackwell, Parvizi used electrical brain stimulation (it’s completely painless) to prove that the fusiform gyrus plays a key role in processing information about faces.

To his own surprise as well as Blackwell’s, Parvizi showed that mild electrical stimulation of two tiny sites in the 2- to 3-inch-long fusiform gyrus on the right side of Blackwell’s brain could cause his perception of faces to instantly become distorted while leaving his perception of other body parts and inanimate objects unchanged.

The push of a button enabling current to flow between those two spots caused Blackwell to immediately exclaim to Parvizi: “You just turned into somebody else. Your face metamorphosed!” As soon as the electrical stimulation stopped, so did the distortion. (Blackwell’s reaction can be viewed in this publicly available video made while Parvizi was pressing the brain-bending buttons. ) ”






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