The patient sits on the bed, his head wrapped in thick gauze bandages. He looks his doctor in the eye and says, “You just turned into somebody else… You almost look like somebody I’ve seen before, but somebody different. That was a trip.”

No, 47-year-old Ron Blackwell hadn’t taken any psychedelic drugs. He wasn’t delirious or psychotic following the brain surgery he had recently undergone. Instead, he was responding to signals from electrodes implanted in his brain to help determine the source of his seizures. By coincidence, the test electrodes had been placed in his fusiform gyrus, the brain region involved in recognizing faces.

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“Your nose got saggy and went off to the left,” Blackwell said, describing the changes he was seeing in his doctor Josef Parvizi’s face in a video released along with a new study. The research, published in the Journal of Neuroscience, was led by Parvizi, who is an associate professor of neurology at Stanford.

While having surgery to treat epilepsy, Blackwell agreed to take part in an experiment led by Parvizi aimed at understanding what the fusiform region actually does and how specific it is to recognizing faces.

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While most people recognize familiar faces rapidly— even if we can’t always put a name to them— up to 3% of the population has a genetic disorder that interferes with recognition, known as prosopagnosia. The condition can also occur after stroke or other brain injury.

In extreme cases, people with prosopagnosia can’t even recognize their own spouses or parents: they simply don’t have the ability to match the visual signals of a person’s face and merge them with the brain’s memory banks to indicate something familiar, and experts presumed this deficit was caused by damage to the fusiform.

Neurologist and bestselling author Oliver Sacks publicly discussed his experience with the disorder, saying that it has contributed to his shyness and avoidance of social situations. Author Heather Sellers wrote about her life with the condition, describing including the havoc it caused in her social life when she once sat down with the wrong date in a bar without realizing it— confusing the individual she had mistaken for her date and infuriating the man she was supposed to be seeing.

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The new study provides the strongest evidence for the potential source of prosopagnosia’s confusing symptoms. The scientists found that the fusiform is specialized for recognizing faces and that stimulating it produces massive distortions in facial perception. Blackwell described seeing faces metamorphose into other faces when the electrodes were turned on. In one case, he said, “It’s like the shape of your face, your features, drooped.” But nothing else was affected. “Only your face changed,” he said, “Everything else was the same.”

When the electrodes were turned off, Blackwell had no unusual reactions. And when he looked at other things like the TV or a balloon, while there was slight distortion, it was nothing like the complete metamorphosis he experienced when he looked at faces.

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“These findings provide evidence for the causal role of these fusiform face regions in face perception,” the authors write. Unfortunately for Blackwell, however, the cause of his seizures was too close to important areas involved in vision for it to be removed. The work does, however, provide intriguing new information about how the fusiform area works, and potentially for how it might be manipulated to help those suffering from not just prosopagnosia but related disorders as well.

Those include Capgras’ Syndrome, in which people are convinced that their friends and family members— sometimes even their pets— have been replaced by identical imposters. While the conditions sounds more like a psychiatric condition, in these cases the problem likely results from a disconnect between the fusiform area and the brain’s emotional regions. When people with Capgras’ Syndrome see people they love— but don’t feel the love and warmth they normally experience — they compensate for the gap by convincing themselves that the people around them are “fake,” or even robots. If their real family members or spouses were there, they reason, they wouldn’t seem so cold and odd.

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For these patients and potentially others who suffer from related symptoms following stroke and brain trauma, the electrical stimulation opens a window into an area of the brain that had been out of reach, and provides hope that their seemingly untreatable symptoms may someday be relieved by less invasive treatments.