You are looking at a woman's face; the contours and features seem so familiar. You see the billowing brown hair, the broad smile, the almond-shaped eyes. You may even be able to describe things about her: Famous talk show host, actress in "The Color Purple," philanthropist.
You feel a familiar pang of frustration because the name seems to be in your grasp, but you cannot come up with it.
The person, of course, is Oprah Winfrey. The inability to conjure the name of such a famous face, for some people, is one of several symptoms of a brain disease called primary progressive aphasia (PPA).
The disease "affects a person's ability to communicate," said Tamar Gefen, a doctoral candidate at the Cognitive Neurology and Alzheimer's Disease Center at the Feinberg School of Medicine at Northwestern University, adding that the disease attacks language centers in the brain.
"Slowly, over time a person loses the ability to name, comprehend, write and communicate," Gefen said.
The loss is not fleeting, but persistent, progressive, and socially crippling. Patients do not just have difficulty naming Oprah, but can have problems recognizing their own family members or friends. All of that makes having an accurate test for the disease important.
Whereas faces presented to patients being tested for PPA used to be people famous in the 1950s, now, more contemporary faces, like Winfrey, Princess Diana, Albert Einstein, Mohammed Ali and Barbra Streisand are being used to test for the disease. Rudy Vallee and James Cagney are also among the faces.
"We created a test that was more suitable for individuals who are now at risk for younger onset dementia," said Gefen.
It makes sense, said Gefen, since for a younger person not knowing the name of someone outside his or her cultural frame may not signal dementia. And PPA is increasingly being diagnosed at a younger age - sometimes as young as 40.
Of course, the research, published Monday in the journal Neurology, was not just about a new dementia test. Gefen and colleagues wanted to trace the pathway of damage carved in the brain by PPA.
They gave the test to 30 people with PPA, and compared them with a similar group without the disease. As predicted, the group with PPA performed significantly worse on tests of face naming, but even more revealing, brain scans of the patients showed brain damage that could explain the poor scores.
It turns out that difficulty naming faces is related to tissue atrophy on the left side of the brain, whereas difficulty recognizing a face is related to damage on both the right and left sides of the brain.
Those areas are distinct from other types of dementia, like Alzheimer's disease, in which different brain areas are affected.
"People hear dementia and think it's an umbrella term used for Alzheimer's disease and memory impairment," said Gefen. "There are distinctly different types of dementia and each points to a different underlying anatomical change."
Clarity about the damage and specificity about the type of dementia may cut down on misdiagnosis of PPA, which is often mistaken for stroke or mental illness, according to Gefen.
And it could also later mean a clear, and specific, treatment.