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Tuesday, November 6, 2012

Understanding face-blindness

Face blindness, or prosopagnosia, is a condition in which people cannot distinguish faces. This highly specific disorder (sufferers have normal vision in all other respects) is thought to be the result of injury or inherited defect in the part of the brain called the fusiform gyrus (shown left). More precisely, the nerve clusters known as pFus and mFus within the fusiform gyrus have been implicated in face blindness. Thanks to the work of Josef Parvizi and his colleagues at Stanford University, and the cheerful participation of epileptic patient Ron Blackwell, we can now confirm this hypothesis.

One treatment for seizure disorders like epilepsy is to pinpoint and excise the exact nerve cluster within the brain that is triggering the seizures. This usually requires a week long stay in the hospital with electrodes positioned near the seizures’ likely focal point. In Blackwell’s case, the likely spot happened to be his fusiform gyrus. In particular, two of the electrodes were positioned to stimulate the pFus and mFus sites within that structure.

When the doctors stimulated those two sites, Blackwell instantly saw a distorted version of the faces in front of him. This happened only when those specific electrodes were triggered, not when nearby ones were turned on or when none were on. Even more intriguingly, the distortions only affected faces. Clothing and objects were unaffected. You can watch this experiment below.

Clearly, the pFus and mFus nerve clusters within the fusiform gyrus are critical for facial recognition. This information may one day help people suffering from prosopagnosia.

Parvizi, J., Jacques, C., Foster, B., Withoft, N., Rangarajan, V., Weiner, K., & Grill-Spector, K. (2012). Electrical Stimulation of Human Fusiform Face-Selective Regions Distorts Face Perception Journal of Neuroscience, 32 (43), 14915-14920 DOI: 10.1523/JNEUROSCI.2609-12.2012