Why Some People Seem Immune to Dementia

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.

Research on Brain Deterioration without Dementia Symptoms

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 structures that characterize Alzheimer’s Disease. Sister Mary, for example, lived to be 101 and continued to perform well on her cognitive tests. But in the autopsy, her brain was filled with plaques and tangles.

Today, health professionals can perform PET brain scans and collect spinal fluid to detect brain problems. They have verified that many people with plaques and tangles still perform well on cognitive tests.

Cognitive Reserve

So you can perform well while your brain is already deteriorating. What causes that mismatch? We believe the answer is “cognitive reserve.”

Cognitive reserve refers to the brain’s ability to compensate for early deterioration. Brain function is dynamic: Neurons communicate with one another to produce our thoughts. Tapping a memory is not like finding a document in a file drawer; memory occurs through a series of pathways between brain cells.

People with greater cognitive reserve can use these networks more efficiently or recruit alternative pathways. Having alternate pathways allows them to continue functioning even when some brain cells or connections begin to deteriorate. Many pathways do not.

Think of a brain with loss of neurons as a house on fire. People who only have one or two corridors are more likely to get trapped near the fire early on. But those who have built numerous pathways can go down different corridors to avoid the fire if one becomes blocked.

How Do You Build Cognitive Reserve?

A host of studies have shown that better early education is associated with lower likelihood of showing symptoms of dementia. A large ongoing study that began with 20,000 high school students in 1972 and 1980 is examining the impact of their education on late-life cognitive health. School-level factors, such as programs, resources, and curriculum, matter. And so do the student’s own attitudes, grades, courses, and subsequent degree attainment.

Other factors also matter when you finish your education, however. Occupational status plays a role. Professions that involve complexity with data, people, or things can increase cognitive reserve. Jobs that involve handling information and ideas, interacting with or managing other people, or working with physical objects, tools, or equipment can also increase cognitive reserve. A surgeon might have a highly complex job regarding information and ideas, interaction with colleagues and patients, and equipment, research, and instruments. By contrast, working in a warehouse may involve repetitive tasks with minimal decision-making.

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Engaging in cognitively stimulating leisure activities is also beneficial. People who spend time reading, attending lectures, and pushing themselves to acquire new skills may also acquire cognitive reserve. When activities involve dealing with new people, the benefits may be greater. (I signed up for an improv course—a new skill, with a new group of people. I’m not very good at “yes and…” but I can feel my cognitive reserve increasing.)

The upshot: Cognitive reserve starts with early-life educational advantages. And advantages in occupational patterns may exacerbate those early benefits. Nevertheless, all is not lost for adults who lack these advantages. Engaging in stimulating activities with others may also contribute to brain reserve.

Is There a Downside to Cognitive Reserve?

There isn’t a downside to cognitive reserve per se. Being able to function despite brain changes is an obvious advantage. But there may be a downside once disease manifests.

Individuals who have cognitive reserve tend to decline quickly once their dementia shows up in cognitive tests and behavior. They go from diagnosis to severe decline at a rapid pace. A possible explanation: People with greater cognitive reserve are diagnosed later in the progression of brain deterioration.

Going back to our house-on-fire analogy, people with only one or two corridors or pathways out of the house find themselves blocked very early in the fire; the house still has a long way before it burns to the ground. But the people with cognitive reserve have many hallways and pathways to avoid the fire. By the time they run out of pathways, the house is burning to the ground.

Lest we finish with a smoldering house and a person trapped inside, keep in mind that many people live their entire lives without showing signs of dementia. The hopeful message is that people may be able to live well and function despite underlying brain deterioration. We still do not fully understand how to stop neuronal deterioration. But cognitive reserve might be the best way to build a fire-resistant house for now.