Korva is a scroll of the internet’s best ideas.
Plaques in the brain, sharp in life
Aging varies widely from person to person. A 100-year-old can be doing really well while a 60-year-old is not, so biological age can't be the only marker.
The nuns, who were all committed to the same profession, made a useful group to compare. When some of them died, their brains showed the hallmark signs of dementia, specifically Alzheimer's disease: plaques and tangles.
Behaviorally, those same women had been functioning like fairly healthy cognitive people. The hardware showed dementia while the behavior didn't, so something else has to be going on.
Some people point to a sense of purpose, and social connections are known to be incredibly important. Physical exercise, sleep, and a positive attitude about aging may also play a role, and people have a certain amount of control over several of these.
How can a brain show dementia without symptoms?
Neurologist Yaakov Stern proposed the idea of cognitive reserve to explain this mismatch. Education, demanding work, and mentally active lives appear to build extra connections, so the brain can route around damage for longer. Two brains with the same amount of physical damage can therefore behave very differently. The nuns studied by epidemiologist David Snowdon, part of the Nun Study that began in 1986, became one of the best-known examples.
What made the nuns such a useful group to study?
The sisters lived in similar housing, ate similar food, and shared a profession, which removed many differences that muddy other aging studies. Hundreds of them agreed to cognitive testing and to donate their brains after death. Snowdon also found autobiographies many had written in their early 20s. How many ideas per sentence a sister packed into her essay predicted her risk of Alzheimer's disease six decades later.
More from Andrew Huberman
