Brain scans hint why elderly forget faces.

As we age, phone numbers elude us, details of that unforgettable summer dim, and new faces don't leave a lasting imprint. Researchers aren't sure whether this age-related forgetfulness results from difficulty in creating memories, retrieving them, or both.

Now, a study examining which areas of the brain bustle with activity during the memorization of faces indicates that older brains may indeed have trouble building, or encoding, memories. During encoding, the study revealed, a number of memory-associated brain regions that jump into action in young people lie dormant in older ones.

"I think these data provide a lot of support for the encoding deficit hypothesis of aging. It seems like the information never gets in to begin with," says Cheryl L. Grady of the National Institute on Aging in Bethesda, Md. Grady, along with NIA colleagues and researchers from the National Institute of Mental Health, also in Bethesda, report their data in the July 14 Science.

Grady's group conducted the study with a scanning technique called positron emission tomography (PET). PET can pinpoint brain regions to which large amounts of blood are flowing--an indication that those areas are active.

Grady and her colleagues worked with two groups of 10 volunteers each, one group with an average age of 25 years, the other 69 years. The researchers took PET scans as the subjects viewed 32 unfamiliar faces for 4 seconds each. After 15 minutes or so, the researchers obtained PET scans while each volunteer looked at faces from the earlier session paired with "distracter" faces and chose the ones he or she recognized.

The young group recognized significantly more faces than the elderly group. PET scans of the younger subjects showed that several regions in the brain flared into activity during memorization. Among those areas was the

hippocampus, which some investigators suggest plays a crucial role in encoding. In contrast, PET scans of the elderly participants showed no elevated activity in areas linked to the encoding process, says Grady.

The images of the older brains resemble PET scans of people trying to memorize something while occupied with another task, notes Fergus I. M. Craik of the University of Toronto. Both groups of people may "lay down records of things they want to learn in a less effective way," he says.