Study identifies five different ways of aging thanks to data from 50,000 brain scans

Lord Kelvin, one of history’s foremost physicists, said that “when you can measure what you are speaking about, and express it in numbers, you know something about it.” If not, he held, “your knowledge is of a meager and unsatisfactory kind.” A search for such precise calculations has motivated much of the considerable technological progress that has taken place over the last 150 years, not to mention the advancement of personalized medicine. This kind of precision health care aims to cure individuals’ particular diseases with personalized treatments. Though it’s not a disease in and of itself, aging impacts all infirmities. Kelvin, who lived in the 19th century and predicted the heat death of the universe using his second law of thermodynamics, knew as well as we do that aging is inevitable. And yet, he was unable to express the process in numbers beyond calendar years, or explain why everyone ages at different rates.

Recently, a team of scientists led by Christos Davatzikos of the University of Pennsylvania published a study in Nature Medicine that identifies the different ways in which our brain deteriorates with the passage of time, pointing the way to a more individualized method for measuring the aging process. Researchers analyzed 50,000 brain scans that revealed five different forms of cerebral atrophy associated with aging and the appearance of neurodegenerative illnesses. Although the human eye is unable to detect the subtle variations between the five patterns, scientists were able to identify them using machine learning technology. The study’s authors trained an algorithm by showing it scans from 1,150 healthy individuals between the ages of 20 and 50, and of nearly 9,000 people total in that age range, both with and without cognitive decline.

Particular forms of aging have to do with individual biological traits, like those that make some people more prone to diabetes and others to cardiovascular disease. But patterns were also detected related to habits, such as alcohol and tobacco consumption. There is also a combination of patterns. People with mild cognitive impairment, which precedes dementia, accumulate features of each pattern, though the presence of one of them was the best predictor of dementia risk in their later years. In general, as was expected, the state of other organs was reflected in the aging of the brain.

Davatzikos warns that this kind of finding does not set the stage for “talking about treatments in the near future.” “This work helps us understand the heterogeneity of brain aging in general, which is caused by several possible underlying pathologies, including Alzheimer’s and Parkinson’s, as well as factors related to cardiovascular and metabolic health,” he said. “For now, the most immediate benefit can be seen in clinical trials, which benefit from recruiting individuals with more homogeneous profiles, something that allows for the detection of more subtle effects of treatment in smaller samples.”

Other recent studies have looked for signs that can help to predict risk of accelerated cognitive decline beginning around 40 or 50 years of age. It’s been found that the hippocampus, a key area in the brain when it comes the creation of new memories, shrinks with age, but that the process can pick up the pace in middle age. Since brain scans are a costly and complicated technique for measuring such changes, there are scientists who have looked for alternative ways to see if the brain’s aging process is accelerating. A team from Johns Hopkins University evaluated cognitive decline in more than 12,000 people over the course of 20 years and compared it to a calculation of their levels of inflammation, which can be measured by blood analysis. They found that individuals whose inflammation levels were in the highest 25% experienced 8% more cognitive decline than those who were in the lowest 25% for inflammation. This effect of aging on the brain, which has a greater impact beginning in the 40s, can be combated with exercise, which has anti-inflammatory effects, and other neuroprotective treatments customized to a specific pattern of brain aging.

In an investigation led by Richard Bethlehem of the University of Cambridge, an international team of scientists attempted to identify the primary changes that take place in the brain throughout life. Among other things, Bethlehem told The Conversation, they saw that our number of neurons grows from before birth until a maximum of six years of age, and begins to descend from there. Our number of cerebral connections continues to grow until 29 years of age and slowly reduces until a person is in their 50s. From then on, the loss of connections accelerates.

Studies like this one and the one that was just published in Nature Medicine look to identify specific changes in the brain that can allow us to standardize the precise measurement of aging in each person. Their objective is to help us rise above that meager and unsatisfactory knowledge of which Kelvin spoke and improve capacity to take action against aging.

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