At first, Kari's brain surgery seemed like a success. The epileptic seizures that had plagued the 23-year-old New Brunswick native for years were finally gone for good.
But something vital was also missing.
And it wasn't until Kari returned to university after a summer of recovery, and stranger after stranger approached to inquire about her surgery, that she made a terrifying realization: "I didn't know my friends."
Kari, who is now 25 and wanted only her first name published, was later diagnosed with prosopagnosia, a condition often referred to as "face-blindness."
Although her eyesight is perfectly fine, the surgery had damaged the part of her brain that uses visual cues to recognize faces, including those of her parents, younger brother and closest friends.
"I just see the general shape," she said, "and I see the hair."
While it was once believed to be rare, researchers now say about 2 per cent of the population may experience some degree of prosopagnosia. People can be born with the condition or acquire it through trauma or illness.
Inherited face-blindness has been studied for some time, and researchers say that new studies of acquired prosopagnosia may also help illuminate some of the most elusive inner workings of the brain, such as how it uses social cues.
Over the past year, Kari and others with acquired prosopagnosia have been travelling from across North America to Vancouver, where they undergo hours of testing as part of a new collaborative study group involving scientists from Canada and Europe.
Researchers hope the assessments will pinpoint which parts of the brain are involved in processing not only someone's identity, but also their age, gender, emotions and whether or not they look physically attractive.
"If we can understand this, we can understand a lot about how the brain parcels out information and processes it," said Jason Barton, a neuro opthamologist at the University of British Columbia who has studied the condition for eight years.
Others say studying the condition may help uncover the biological underpinnings of other cognitive disorders, including autism.
Prosopagnosia was first documented in 1947 by a German doctor who observed that a soldier who had suffered a bullet to the head had lost his ability to recognize people.
Until recently, the condition was believed to be very rare. But in the past couple years major studies have suggested that up to one in 50 people has some degree of face-blindness.
"I think it will become recognized as a real major malady or condition that causes people all kinds of trouble," said Ken Nakayama, a professor at Harvard University's psychology department whose research put the figure at around 2 per cent.
Rob Cross, 25, acquired prosopagnosia four years ago when a virus attacked his brain.
For years, he has hidden his condition by avoiding calling his co-workers at a Burnaby manufacturing company by name, or acting slightly aloof.
"Every morning people say, 'Hi Rob,' and the majority of the time I don't know who it is," said Mr. Cross, who hasn't made many new friends since his illness.
"They just get the impression that I'm really conservative."
People who are face-blind encounter potentially embarrassing situations daily. To cope, most have developed tricks to help them identify others.
When Kari meets somebody, she notes their location. If she's at school, for example, it's probably a classmate. Then she looks for other clues: hairstyle, mannerisms, body structure, whether the person wears glasses or jewellery. She'll listen carefully to voices and note how people move. In the winter, she'll memorize people's coats.
Still, Kari dreads visiting the close-knit village where she grew up, preferring instead to melt into big cities where she isn't expected to know anyone.
She might study with classmates all day, then bump into them at the mall 30 minutes later and not know who they are.
At a recent family reunion hosted by her parents, she struggled to recognize relatives she's known since childhood.
"I spent most of the time in my bedroom," she said. "It was just so frustrating."
Much of the research on face-blindness take place at the Prosopagnosia Research Centers at Harvard and University College London.
Brad Duchaine, who was previously at Harvard but moved to London two years ago, helped to establish which parts of the brain appear to be critical for face recognition - the fusiform face area and the occipital face area, located toward the back of the brain.
Still, scientists aren't sure whether other parts of the brain are involved. They say research into prosopagnosia may yield insights into how and where the brain processes other bits of information from a face, including who that person is, their gender, how old they are, what they're feeling, and whether they are attractive.
"It's clear that there are a number of different brain areas that are important for face processing," Dr. Duchaine said. "But we don't know what these different areas are doing. So by correlating where someone has a lesion with what different impairments they have, you can learn a lot about what specific areas are doing."
Now, Dr. Duchaine is pairing up with an old Harvard colleague - Dr. Barton, a Canadian who is now at UBC - to conduct tests with prosopagnosia patients, including scanning their brain while showing them images of faces and other objects.
In a recent study, the UBC researchers discovered that the same area of the brain that identifies people may also be involved in judging attractiveness, Dr. Barton said.
Potential test subjects, the researchers say, are sprinkled around the world. Some may not even realize they have the condition. They're being recruited through referrals and Dr. Duchaine's website, Faceblind.org, which has a test people can take to see if they have some degree of face-blindness.
About 50 possible subjects have already been identified, Dr. Duchaine said.
One of them is Kari and another is Mr. Cross. Asked why he volunteered to subject himself to the prodding of scientists, Mr. Cross answered with a laugh. "Well," he said, "I don't like having prosopagnosia."
FORGETTING FACES
Prosopagnosia, or face-blindness, is a neurological condition in which a person with normal eyesight is unable to recognize faces because the part of the brain dedicated to face recognition is impaired.
The visual cortex areas are located in the parietal and temporal regions of the
Prosopagnosia is generally associated with errors that occur along the neural pathways between the fusiform gyrus area of the brain and the visual cortex.
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