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It's no secret that people become forgetful in old age. However, new research reveals physical evidence for this aging absent-mindedness. Scientists found that brain regions linked to memory shrink as people get older. However, researchers said the decrease is more pronounced in people who go on to develop neurodegenerative disease.

Researchers said that the latest study suggests that volume reduction is associated with overall decline in cognitive ability and with increased genetic risk for Alzheimer's disease. 

"Our results identify a specific pattern of structural brain changes that may provide a possible brain marker for the onset of Alzheimer's disease," Nathan Spreng, assistant professor of human development at Cornell University, said in a news release.

The study involved brain data from 848 individuals spanning the adult lifespan. Some of the participants were assessed multiple times over several years, which allowed researcher to measure brain changes over time and determine who did and did not progress to dementia.

Scientists found that volume in the brain network associated with internally generated thoughts like memory declined in both healthy and pathological aging. However, the greatest decline was seen in Alzheimer's patients and in those who progressed from mild cognitive impairment to Alzheimer's disease.

The study found that shrinking of brain volumes in these regions were associated with declines in cognitive ability, the presence of known biological markers of Alzheimer's disease and with carrying the APOE4 variant of APOE gene, a known risk factor for Alzheimer's.

"While elements of the default network have previously been implicated in aging and neurodegenerative disease, few studies have examined broad network changes over the full adult life course with such large participant samples and including both behavioral and genetic data," said Spreng. "Our findings provide evidence for a network-based model of neurodegenerative disease, in which progressive brain changes spread through networks of connected brain regions."

The findings are published in the Journal of Neuroscience.