As life expectancy continues to increase, more and more people will reach and surpass the century mark in age. But even as greater numbers reach and surpass the 100-year milestone, little is known about what constitutes normal levels of cognitive function in the second century of life.

Led by Adam Davey, associate professor in Temple’s Department of Public Health, a group of researchers used a new method called factor mixture analysis — a statistical technique for identifying different groups within a population — to identify the prevalence of cognitive impairment in centenarians and try to understand the cognitive changes that are part of extreme aging. They published their findings, “Profiles of Cognitive Functioning in a Population-Based Sample of Centenarians Using Factor Mixture Analysis,” in the journal Experimental Aging Research.

“One of the motivations for studying centenarians is that they are very close to the upper limit of human life expectancy right now,” said Davey. “By looking at their cognitive functioning we can learn a lot in terms of how common or prevalent cognitive impairment is among that age group.”

Using voter registration lists and nursing home records in 44 counties in northern Georgia, the researchers identified 244 people between the ages of 98-108 — approximately 20 percent of all centenarians living in that region — who participated in the study. Participants were assessed based on a series of standard tests used to measure cognitive functioning.

“As people get into later life and the prevalence of cognitive impairment becomes relatively high, we need some way of distinguishing between those people who are aging normally and the people who have cognitive impairment, which could indicate dementia,” said Davey.

The researchers found that even though approximately two-thirds of centenarians were at or below the threshold for cognitive impairment by one commonly used measure, only one-third of centenarians were identified as cognitively impaired using their new approach.

“That’s consistent with the level of cognitive impairment found in another study that looked at people up to the age of 85-plus,” said Davey. “But even the normal folks have had cognitive declines to the point that they are functioning at a level that would indicate impairment at younger ages.”

The researchers found that characteristics such as age, race and educational attainment can help to distinguish those in the lower cognitive performance group.

“This is the first study that I’m aware of that allows us to distinguish between these two groups of centenarians, so that we can start to develop benchmarks for what is normal cognitive functioning among members of this age group,” said Davey. “These people have lived so long that even their normal cognitive function could be mistaken for a form of dementia if a physician were to treat them as they would someone who was merely old.”

In addition to Temple, the study included researchers from Wayne State University, University of Georgia, Osaka University, Iowa State University, Brigham and Women’s Hospital, Harvard Medical School and the University of Colorado.

The study was funded by grants from the National Institutes of Health.