This theory resulted from a study published in the Annals of Neurology in the late 1980s, which raised questions about why some people develop symptoms of Alzheimer's disease and some don't. Autopsies were conducted on 137 former nursing-home patients.
As expected, the brains of those who had demonstrated symptoms of Alzheimer's were filled with plaques (brain deposits made up of dead cells and proteins) and tangles (nerve cells that had become tangled together) — characteristic physical signs associated with the disease.
Here's the unexpected part: The brains of ten patients who didn't show any symptoms of Alzheimer's contained the same level of plaques and tangles. If the physical reasons for the disease were present in those people, why didn't they get the symptoms?
There was another twist as well: The ten patients in question had heavier brains and more neurons than they should have given their age.
In other words, the more you use your brain, the greater your chances of avoiding symptoms of Alzheimer's.
Strong stuff, huh?
Obviously, no one is offering guarantees here. There's no guarantee that anything will add X number of years to your life, and that those years will be free of any symptoms of memory loss or other mental decline. But study after study in the past few decades has shown that mental activity can — and often does — have a positive effect on your quality of life in the long run.
How do you build a cognitive reserve? The same way that you keep your synapses happy and healthy. Keep reading and learning.