Why can’t the brain regrow neurons?

Alzheimer’s kills brain cells. Can we help the brain make new ones?

By: Simon Spichak

If you scrape your knee or break a bone, new cells repair the damage before you even know it. Other organs in the body are even better at regrowing themselves: The cells lining the gut regenerate every three to four days

In contrast, the brain has a limited capacity to regenerate and repair itself. Even when brain cells begin to die off in Alzheimer’s or other types of dementia, there aren’t nearly enough new cells dividing and surviving to repair the brain.

Up until the mid-20th century, scientists believed that no new brain cells at all formed over the lifetime. But in the 1960s and 1970s, scientists discovered cells in the brain dividing to form new cells: a process called neurogenesis. But as we age, the rate at which our brains can form these new neurons decreases. When new cells do form, they originate near the hippocampus, a region of the brain important for memory — one affected early on in Alzheimer’s

In 2019, a study found that among people with Alzheimer’s, those with more neurogenesis — more new brain cells being formed — did indeed have less cognitive impairment. These findings came with an exciting realization: If we increase the brain’s ability to regenerate brain cells, could it make up for the cells that die off in Alzheimer’s and stave off the symptoms of cognitive decline and dementia?

Researcher María Llorens-Martín, PhD, at the Autonomous University of Madrid, thinks so: Her research so far shows promise for the idea that neurogenesis may hold the key to figuring out what causes Alzheimer’s and how to diagnose it early. 

“What is failing in the environment that is making these neurons die prematurely or making it very difficult for them to get connected appropriately?” she said in an interview with The Scientist

New brain cells need a supportive environment to thrive and function.

In 2020, another research group completed a study which found that stimulating the production and survival of new neurons in mouse models of Alzheimer’s did in fact improve cognition. Their researcher found that brain-derived neurotrophic factor — a signaling molecule that helps neurons grow — even mimicked the effects of exercise on cognition.

But what if you could skip one of these steps altogether? Transplanting brain cells grown in a dish could quickly boost the amount of new neurons integrating into the brain, researchers believe. It might also speed up cognitive recovery.

In 2022, a study in dogs with a canine cognitive dysfunction found that injecting neuronal precursors into the memory center of their brain could reverse some of the decline. As a result, human trials of this approach will kick off in the next few years.

 

So far, this work raises more questions than it answers. But down the line, researchers hope to find the answer to whether it’s possible to harness the brain’s own regenerative ability to treat or halt the progression of Alzheimer’s.

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