James' World 2

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The brain is a well-designed machine. If it’s working well—like when it’s reading the words on this page—we don’t notice it at all. At night when we sleep, the brain takes our consciousness offline so it can start its real work: sorting through the day’s information, storing the important parts, and cleaning out the gunk that accumulated.

The brain is so well-designed, in fact, that we hardly even notice when it’s breaking down. 

Like the rest of our organs, the brain undergoes its own aging process. And yet the majority of adults don’t experience major cognitive decline—the kind that severely limits their ability to live independently—over time. 

That’s because the brain is one of the most resilient organs in the body. Yes, dementia affects about 5.6% of the world’s population, a share that includes the devastating burden of Alzheimer’s disease. But in normal aging, even as parts of the brain shrink and neurons lose connection with each other, those changes only have a minor effect on our daily lives. It may be frustrating to forget where you put your keys, but you can still learn that you’re prone to forgetting them, and pick up the habit of writing notes for yourself. 

For adults who remain neurologically healthy into their later years, the brain constantly adapts and even thrives under new conditions. But how it pulls it off is a mystery scientists are still trying to solve. The hope is that if researchers can understand how healthy brains stay resilient, they can identify what’s happening when these systems fail—often, leading to dementia. 

Never Constant

The brain’s incredible resilience comes, at least in part, from its plasticity. The rest of the body’s organs carry out roughly the same job from the moment we’re born—albeit on a larger scale as we grow. The heart pumps blood, the liver and kidneys filter, and the stomach churns food.

Not the brain.

Babies’ brains are equipped with billions of neurons, but they have to be warmed up and molded to be useful. Over as many as 25 years, neurons form hundreds of thousands of connections as we learn and make memories. Some of these connections are cropped as they’re not needed; others grow stronger as we learn to reason in the abstract, mitigate impulsive and risky behavior, and plan ahead for the future. 

Shortly after the brain finishes fully forming, though, it starts to wear down. 

“Aging is a lifelong biological process,” says Kristin Kennedy, a neuroscientist at the University of Texas at Dallas who studies healthy cognitive aging. There’s some disagreement about exactly when the brain starts to show signs of wear and tear. Some of the limited research available suggests it happens around middle age, some suggests our 30s, and some even in our 20s. But the consensus is that some shrinkage is inevitable and normal. Specifically, the prefrontal cortex and medial lobes—areas involved with high-level functions like planning, emotional processing, learning, and memory—get a little smaller, says Elizabeth Zelinski, a neuroscientist and gerontologist at the University of Southern California. 

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For most, the brain constantly adapts and even thrives under new conditions. Photo by Hokyoung Kim for Quartz

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