Good morning,

How is your weekend going?

I found my way down some very long dirt roads to the northern edge of the Grand Canyon. Thankfully, the dispersed campsite of my dreams was vacant. They may have to drag me out of here. This was my campsite coffee spot yesterday morning:

Here’s what I have for you today:

• One big thing. Some nuns had advanced Alzheimer’s yet no symptoms. What protected them — and how can you build the same hidden strength in your own brain? 🧠

Ready to jump in? 🦘

1️⃣ ONE BIG THING

Investing in your cognitive reserves.

Imagine two neighbors, Bob and Steve, start building new houses at the same time.

Both are building three-bedroom houses with identical floor plans. Once the foundations are poured, Bob and Steve begin framing their new houses with lumber. They use big 2x6 boards for the main beams and 2x4s for additional support.

Bob is a cautious man. He likes to be on the safe side, to add redundancies. So, on every wall of the house, Bob adds far more 2x4s than the house plan calls for. He also adds additional beams and cross-braces for extra support. He ends up using almost twice as much lumber as Steve.

Eventually, the roof is added, and the walls are covered and painted. The two houses, now complete, look identical from the outside, but we know Bob's house has far more internal support.

Fast forward fifty years. Without Bob or Steve noticing, both houses have termites. For the sake of my example, let's imagine both houses have exactly 100 termites happily gnawing away on the wooden innards of these houses.

Whose house is going to topple over first?

In Bob's overbuilt house, he can afford to lose the structural support of a 2x4 here and there. On the other hand, Steve's house will buckle once a few critical support boards are destroyed.

Structural redundancies in your brain.

Bob and Steve’s termite-riddled wooden houses are a nice analogy for big idea I think everyone in midlife needs to understand about dementia.

This changed how I think about dementia and what you can do to avoid or delay symptoms. And no, it won't entail doing more Sudoku.

Let’s pause briefly to contrast dementia and Alzheimer’s:

Dementia is a broad term for symptoms like memory loss, confusion, and difficulty thinking clearly. It describes what a person experiences, not what’s causing it.

Alzheimer’s disease is the most common cause of dementia, responsible for about two-thirds of cases. It refers to a specific biological process in which amyloid plaques, tau tangles, and other changes damage brain cells.

So, dementia is a range of symptoms, while Alzheimer’s is a common cause of these symptoms.

You could say dementia is like having a fever (symptom), while the influenza virus causes the fever.

Now, what if I told you certain people experience the underlying disease that is Alzheimer’s without exhibiting many of the symptoms? In effect, it is like they have influenza but no fever.

To understand how this works, let’s look at 678 nuns.

What can we learn from the brains of nuns?

In 1986, David Snowdon of the University of Minnesota began an iconic study of 678 nuns from the Sisters of Notre Dame. Snowdon chose nuns as participants because of their similar lifestyles, with few variables like smoking or alcohol. This made it easier to study how other factors, such as cognitive ability, affected health.

All the nuns were 75 or older when the study began. It followed them for more than two decades. Researchers regularly tested their memory, thinking, and overall health. When the participants died, they donated their brains for analysis so scientists could compare their cognitive function with what had actually happened to their brains.

The results of this research surprised everyone involved.

In many cases, the brains showed all the classic signs of advanced Alzheimer’s disease: sticky amyloid plaques, twisted tau protein tangles, and significant tissue loss. On the surface, the damage was what doctors would expect to see in someone with severe dementia.

Yet many of these women had shown no signs of cognitive decline while they were alive. They continued to teach, write, read, and think clearly well into old age.

In effect, some of the nuns had the causes of neurodegenerative disease, but had no symptoms. They had influenza but no fever.

To understand why, let’s return to our homebuilders Bob and Steve.

The power of cognitive reserves.

The Nun Study showed that some nuns had built up and maintained cognitive reserves throughout their lives. These particular nuns aced cognitive tests throughout their lives, and yet brain exams after they died showed significant damage consistent with Alzheimer's disease.

Doctors refer to this as clinically silent Alzheimer’s disease. Their brains kept functioning even when damage was present.

To understand cognitive reserves, think back to Bob's house. He built his structure with many redundant support beams and lots of cross-bracing. With these redundancies built in, termites eating away at some of the house's support structure did not lead to the house falling down.

For me, this feels like quite a revelation. Dementia is scary. If you live to be 80, you will likely have the symptoms of dementia or care for someone who does.

Building up your cognitive reserves.

How exactly do you create cognitive reserves? For better or worse, while a few crossword puzzles may help, this is not enough.

The Nun study found that cognitive reserves are not created late in life—they come from the cumulative effect of mental activities throughout life.

The nuns who had the strongest cognitive performance late in life (despite some having damaged brains) had the following traits:

• Higher educational attainment: More years of formal education.

• Early-life linguistic complexity: Richer language and higher idea density in young adulthood (based on examination of past writing samples).

• Active social and community life: Daily interaction and communal living throughout life.

Many roads lead to the answer.

Let’s imagine a different way to understand this idea.

The average brain contains more than 100 trillion synapses, the connection points where neurons communicate. These connections are not fixed. They form, strengthen, weaken, and disappear throughout life in a process known as neuroplasticity. Every time you learn something new or engage deeply with a complex idea, new synapses form and existing ones strengthen.

If you only store a single fact about a topic, and the disease destroys the connection that holds it, the information is lost. If you have built multiple connections to that same piece of knowledge, the brain can use alternate pathways to find it.

This network effect explains why some people maintain normal thinking and memory even when the disease is damaging parts of their neural system.

The nuns bolstered this protective reserve through a lifetime of mentally demanding work. They taught lessons, read and wrote daily, and engaged in meaningful conversations that challenged their thinking. These activities built a surplus of neural connections. Even when some connections failed, others were still available to take over.

Building cognitive reserves in midlife.

I will save several more fascinating aspects of this story for next week. They relate to the special types of activities you can do in midlife and later to build new neural connections—in effect, new deposits to your cognitive reserves.

They include:

• Why does novelty expand neural connections in ways that already learned activities do not? For example, a trip to a new city helps more than returning somewhere you have already been.

• Why do new behaviors that have meaning to you expand mental capacity in ways that things you don't care about do not? Example: Why finally learning Spanish to live in Spain (which you have always dreamed about) is better than learning a new regulatory framework at work.

•  Why do social interactions have one of the biggest impacts of all?

Closing notes and inspirations.

Today’s letter built on my thoughts from last week’s Your Livewired Brain, which was informed by David Eagleman’s book Livewired.

Eagleman covered the Nun Study in his book, which led me down the rabbit hole of that research, which led me to the work of Lisa Genova, neuroscientist and author of Still Alice.

Do yourself a favor and watch her wonderful TED talk:

Thanks for reading today.

Have a great Sunday,

Kevin

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