By Elizabeth Norton

The ability to recognize faces is so important in humans that the brain appears to have an area solely devoted to the task: the fusiform gyrus. Brain imaging studies consistently find that this region of the temporal lobe becomes active when people look at faces. Skeptics have countered, however, that these studies show only a correlation, but not proof, that activity in this area is essential for face recognition. Now, thanks to the willingness of an intrepid patient, a new study provides the first cause-and-effect evidence that neurons in this area help humans recognize faces—and only faces, not other body parts or objects.

An unusual collaboration between researchers and an epilepsy patient led to the discovery. Ron Blackwell, an engineer in Santa Clara, California, came to Stanford University in Palo Alto, California, in 2011 seeking better treatment for his epilepsy. He had suffered seizures since he was a teenager, and at age 47, his medication was becoming less effective. Stanford neurologist Josef Parvizi suggested some tests to locate the source of the seizures—and also suggested that it might be possible to eliminate the seizures by surgically destroying a tiny area of brain tissue where they occurred.

Parvizi used electrodes placed on Blackwell's scalp to trace the seizures to the temporal lobe, about an inch above Blackwell's right ear. Then, surgeons placed more electrodes on the surface of Blackwell's brain, near the suspect point of origin in the temporal lobe. Parvizi stimulated each electrode in turn with a mild current, trying to trigger Blackwell's seizure symptoms under safe conditions. "If we get those symptoms, we know that we are tickling the seizure node," he explains.

Certain electrodes, however, produced a dramatically different result from the colors and memories that Blackwell typically experienced. When Parvizi sent a signal through these electrodes on the fusiform gyrus, Blackwell told him, "You just turned into somebody else. Your whole face just sort of metamorphosed." When the stimulation was halted, Blackwell reported that Parvizi's face had "returned" to normal. The same test caused Blackwell to perceive unsettling distortion in the face of Parvizi's assistant. (See accompanying video.)

But the electrode stimulation affected only Blackwell's perception of faces of people he could see in person. Stimulating the two points also produced no change in Parvizi's suit, tie, or skin color, or in other objects around the room.

While the electrodes were in place, Parvizi got Blackwell's permission to turn the clinical probe into a research study, described online tomorrow in The Journal of Neuroscience. Teaming up with Stanford neuroscientist Kalanit Grill-Spector, who studies the brain areas important in facial recognition, he scanned Blackwell's brain using functional magnetic resonance imaging (fMRI) and confirmed that the two electrodes that influenced Blackwell's perception of faces were at points in the fusiform gyrus implicated by Grill-Spector's previous research. The researchers also recorded brain activity using the electrodes they'd placed on Blackwell's brain with a technique called electrocorticography. They found that the activity picked up by the electrodes at the two "hot spots" tracked with peak activity at these sites, as measured by fMRI.

Cognitive neuroscientist Juan R. Vidal of the Lyon Neuroscience Research Center in France applauds the authors' use of multiple methods and says the study is the first to prove that the fusiform gyrus plays a causal role in face perception. Previous studies only showed that the area is involved, Vidal says. "The complementary evidence of electrocorticography, fMRI, and brain stimulation will make it possible to study not only the effects of brain stimulation on the local neural networks that process face information, but also how they broadcast their information towards other regions in the brain."

ScienceNOW, the daily online news service of the journal Science

Also on HuffPost:

The Power of the Subconscious Mind, by Leonard Mlodinow
Loading Slideshow...
  • Faces

    Faces play a special role in human behavior. As a result there is a discrete part of the brain - the fusiform face area - that is used to analyze faces, and much of the processing is outside our awareness. Look at these photos of President Barack Obama. The top pair looks like two upside-down shots of the President, but the photo on the left of the right-side up pair looks horribly distorted. In reality the bottom pair is identical to the top pair, except that the top photos have been flipped. Your brain devotes special attention (and neural real estate) to faces - but not upside down faces, since we rarely encounter those, except when performing headstands in a yoga class. That's why we are far better at detecting the distortion on the face that is right-side-up.

  • Love

    <em>How do I love thee?</em> Elizabeth Barrett Browning felt she could count the ways, but chances are, she couldn't accurately list the reasons. Today we are beginning to be able to do just that - and the answer is surprising. For example, we have a natural subliminal affinity for - and bias toward - anything having to do with ourselves. Have a look at the following table. It shows who has been marrying whom in three states of the Southeastern United States. Listed along the horizontal and vertical axes are the five most common U.S. surnames. The numbers in the table represent how many marriages occurred between bride and groom with the corresponding names. The largest numbers, by far, occur along the diagonal - that is, Smiths marry other Smiths and so on.

  • Sight

    The science of the mind has been remade by a tool that emerged in the 1990s, functional magnetic resonance imaging, or fMRI. fMRI offers 3-dimensional pictures of the working brain, inside and out, mapping to a resolution of about a millimeter, the level of activity throughout. To get an idea of what fMRI can do, consider this: scientists can now use data collected from your brain to reconstruct an image of what you are looking at. Look at the pictures below. In each case, the image on the left is the actual image a subject was gazing at, and the image on the right is the computer's reconstruction, based on the fMRI's electromagnetic readings of the subject's brain activity.

  • Touch

    We all know how it effects us when a lover strokes our skin, but studies show that even a brief, light touch that we hardly notice - and quickly forget - can exert a powerful unconscious influence on our behavior toward the person who touched us. Touching has been found to increase the fraction of single women in a night club who would agree to a request to dance, the number of people agreeing to sign a petition, and the average tip given servers in a restaurant. We are now beginning to understand how touch works its magic: a particular kind of nerve fiber in people's skin - especially in the face and arms - transmits the pleasantness of social touch. Those nerve fibers are connected directly to areas of the brain associated with emotion.

  • Brand Preferences

    Pepsi consistently beats Coke in blind taste tests, although people seem to prefer Coke when they know what they are drinking, an effect called the "Pepsi paradox". New brain imaging studies found that an area of the brain called the ventromedial prefrontal cortex, or VMPC, is the seat of the good feelings we experience when we contemplate a familiar brand-name product. And so in 2007, researchers recruited a group of participants whose brain scans showed significant VMPC damage, and also a group whose VMPC was healthy. Those with healthy brains indeed preferred Coke when they knew what they were drinking. But those who had damage to their VMPC - their brain's "brand appreciation" module - preferred Pepsi, just as they did in the blind taste tests. Apparently it is the unconscious warm and fuzzy feeling people have toward the brand Coke that explains the Pepsi paradox.

  • Social Preferences

    The experience of feeling socially connected to others starts very early in life. Even 6-month-olds make judgments based on what they observe of social behavior. In one study infants watched as a "climber", a disk of wood with large eyes glued onto its circular "face," started at the bottom of a hill, and repeatedly tried but failed to make its way to the top. After a while, a "helper," a triangle with similar eyes glued on, would approach from further downhill and help the climber with an upward push. Other times a square "hinderer" would approach from uphill and shove the circular disk back down. The infants, unaffected and uninvolved bystanders, copped an attitude toward the hinderer squares: when offered a chance to play with the objects, they avoided the squares, and chose the helper triangles. <em><a href="http://www.flickr.com/photos/pinksherbet/4269396864/sizes/l/in/photostream/" target="_hplink">Flickr photo courtesy of Pink Sherbet Photography</a></em>

  • Social Judgments

    Vested interest plays a powerful unconscious role in determining our "sincere" social judgments. In one experiment researchers randomly assigned volunteers to the role of plaintiff or defendant in a reenactment of a lawsuit. Both sides received documents regarding a real case involving an injured motorcyclist and the driver who hit him. The volunteers were paired up and asked to negotiate their own version of a settlement. They were also offered a cash bonus if they could guess - within $5000 - what the judge had actually awarded the plaintiff. Could they ignore their assigned role as advocates, and make an objective guess? No: On average, the volunteers assigned to represent the plaintiff's estimates were double those made by those assigned to represent the defendant.