Beth Stevens, a neuroscientist, is a newly appointed MacArthur Fellow. (John D. and Catherine T. MacArthur Foundation)

Newly crowned MacArthur Fellow Beth Stevens is into remodeling — but not the kind that requires a hard hat. In her neuroscience lab at Boston Children's Hospital's F.M. Kirby Neurobiology Center, she watches the brain’s fastest-moving cells flit from synapse to synapse in developing brains. Her discoveries about these tiny cells have launched her into an entirely new field, suggesting that brains are even more complex and amazing than anyone previously thought.

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The cells in question are called microglia, and they’re all over the brain. Until recently, common wisdom was that they were part of the immune system, defending the brain against invaders and cleaning up after disease. That is, until Stevens got her hands on them.

As a graduate student, Stevens became intrigued by the cells. She wondered why they tidy up in some places, but not others. Then, she discovered that they’re doing more than just cleanup: They’re remodeling the brain.

In the developing brain, she explains, “synaptic connections form early on and many of them get whittled or pruned.” This pruning is important for precise brain wiring and sets the stage for healthy development, but nobody knew how pruning worked. “Everyone knew about microglia,” says Stevens, but nobody thought they were involved in brain wiring.

“These molecules can wear different hats,” she says. “It can’t be a coincidence that we have all of those immune molecules in the brain during development.” By visualizing the brain while synapses were being pruned, Stevens was able to prove their role in whittling away extra synapses.

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Now, she thinks that microglia may reactivate during adulthood, causing neurodegenerative diseases like Alzheimer’s. Her lab is trying to demonstrate that when microglia malfunction, they can prune too many synapses and lead or contribute to conditions like autism, schizophrenia or other brain disorders.

And maybe the cells have other functions, too. “Pruning is probably the tip of the iceberg,” says Stevens. By integrating neurology and immunology, she says, scientists could discover a whole host of alternative functions of cells they’ve known about for years.

So what’s it like mashing up two scientific disciplines? “I’m in completely uncharted waters,” she laughs. And she likes it. As a young scientist, pursuing unasked questions gives her a wide-open field that’s hers for the taking. “Science can be quite competitive, and that’s attractive to me,” she says. “I’d rather be leading the charge instead of being one of the herd.”

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Armed with $625,000 in grant money and new prestige, she hopes to translate her windfall into funding for higher-stakes projects her lab might not otherwise pursue. But she also plans to use some of the funds to chase success “as a person, not a scientist” — something she measures in terms of balance, not recognition.

As the only woman in this year’s class of scientists, Stevens feels obligated not just to juggle work, family and science but to teach others what she’s learned. She wants to use her award to highlight her challenges along with her successes, she says. Other women in the field “are all wondering how they are going to do this,” she says. “Run a lab, run a family — it’s particularly hard in science.”

Stevens doesn’t claim to have it all figured out (she admits that she wouldn’t necessarily want to relive her early days starting a lab and having two children). Instead, she says it’s her responsibility to tell the truth to other women in science. “It’s hard, but it’s worth it,” she says. “I try to be honest with people — it wasn’t easy.” Then again, neither is remodeling the way scientists think about the brain.

Erin Blakemore (@heroinebook) is a freelance journalist from Boulder, Colo. She is the author of "The Heroine’s Bookshelf" (Harper). 

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