Dementia is linked to changes in the brain. Health professionals used to assume that brain damage and dementia symptoms always went hand in hand. More recent research, however, shows that some people have significant brain damage yet never develop dementia. How can that be?

In a previous post, I shared that dementia is defined by the inability to function in everyday life, such as getting lost in familiar places, having difficulty managing finances, forgetting to turn off the stove, or struggling with basic tasks. These symptoms stem from underlying brain deterioration, including damage to brain cells (neurons) and structures.

Neurons normally communicate in networks that support healthy thinking and behavior. In dementia, neurons are damaged or dying, disrupting communication across the brain. The brain may have protein accumulations such as what we call plaques and tangles in Alzheimer’s Disease. When dementia symptoms appear, the brain is no longer functioning effectively.

At some point, researchers realized that their assumptions were incorrect: The brain could be deteriorating and people could still function well in daily life and on cognitive tests.

The Nun Study discovered a disjuncture between brain structure and cognitive performance in the 1990s. At the time, scientists could only confirm a diagnosis of Alzheimer’s Disease after death. Over 670 Catholic nuns from the School of Sisters of Notre Dame, aged 75 and older, agreed to do yearly cognitive tests, and to donate their brains for autopsy when they died.

Some of the nuns who tested within a normal range of cognition when they were alive had brain........

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