Two tiny brain areas are key for seeing and recognizing faces, according to a new study that sheds light on a rare neurological disorder known as facial blindness.
Stanford University neuroscientists used electrical pulses to tickle the brain areas, called the mid and posterior fusiform gyri face-selective regions.
"Your nose got saggy and went off to the left," study subject Ron Blackwell said, describing a deliberately distorted face in a video accompanying the study. "You just turned into somebody else. Your face metamorphosed."
Blackwell, 47, volunteered to be zapped after having electrodes implanted in his brain to identify the source of his seizures, according to the study. By sheer luck, two of the electrodes were placed in the right fusiform gyri.
"It warped. It kind of stretched and dropped," he said of the electricity's effect on his perception of a person's face. But "only your face changed… Everything else was the same."
The distorted image vanished when the electrical pulses stopped, Blackwell reported.
The study, published today in the Journal of Neuroscience, offers the first direct evidence that the brain areas are crucial for facial recognition. It also suggests abnormal brain activity in those areas can trigger distorted perceptions of the outside world.
"All reality is in our brain," study author Dr. Josef Parvizi, a neurologist and associate professor of neurology at Stanford, wrote in an email to ABCNews.com. "Any abnormal activity (i.e., abnormal electrical firing of neurons) will lead to illusions and even delusions."
The researchers used sham pulses and brain imaging tests to confirm the findings, which held up across multiple faces, according to the study.
"It's really a spectacular finding in this field," said Nancy Kanwisher, a professor of cognitive neuroscience in the department of brain and cognitive sciences at Massachusetts Institute of Technology, who was not involved with the study. "It's a rare and precious case in which we can show that a part of the brain is actually a critical part of the machinery we use when we see faces."
The study also suggests that the mid and posterior fusiform gyri face-selective regions are not involved in the perception of features other than faces, Kanwisher added.
These results may someday help the one to two percent of the population who suffer from prosopagnosia, better known as facial blindness. People with the disorder, which can be present at birth or acquired though brain injuries or disease, have difficulty recognizing friends, family members, and even themselves, according to the National Institute of Neurological Disorders and Stroke website.
For now, the results illuminate the inner workings of the complex machine that is the human brain.
"This finding provides a dramatic demonstration of the idea that the human brain is like a 'Swiss army knife,'" said Kanwisher. "We have many specialized kinds of intelligence, each dedicated to a very specific kind of task."