Humans have evolved an ability to recognize faces, and this ability is so important that there is an area in the brain, the fusiform gyrus, solely dedicated to this task. Brain imaging studies have consistently shown that this region of the temporal lobe becomes active when people look at faces.
A new study provides the first cause-and-effect evidence that neurons in this area can help humans to recognize only faces, not body parts or objects. The scientists published their findings in The Journal of Neuroscience.
Two locations in the brain’s fusiform gyrus respond to faces (red) but not to other objects (yellow). Credit: J. Parvizi et al., J. Neurosci, Advance Online Edition (2012)
This feat was accomplished by the unusual collaboration between a researcher and an epilepsy patient, Ron Blackwell, an engineer in Santa Clara, California, who came to Stanford University in Palo Alto, California, in 2011 seeking a better treatment. He had been suffering seizures since his teens, and his medication was becoming less effective. Stanford neurologist Josef Parvizi suggested some tests to determine the source of the seizures. He also suggested that it might be possible to eliminate the seizures by surgically destroying a tiny area of the patient’s brain.
Parvizi used electrodes to trace the seizures to the temporal lobe. Surgeons then placed electrodes on the surface of Blackwell’s brain to stimulate specific areas of the temporal lobe in order to determine exactly where the seizures stemmed from. Electrodes placed on the fusiform gyrus changed the facial recognition ability of Blackwell. While being stimulated, he reported seeing Parvizi’s whole face just sort of metamorphose and the electrode stimulation affected only Blackwell’s perception of faces of people he could see in person. The stimulation produced no change in Parvizi’s suit, tie, or skin color, or in other objects around the room and Parvizi’s face returned to normal when stimulation ceased.
The scientists scanned Blackwell’s brain using functional magnetic resonance imaging (fMRI) and confirmed that the two electrodes that influenced Blackwell’s perception of faces were points in the fusiform gyrus.