MADELEINE BRAND, host:
From NPR News, it's DAY TO DAY. Alex, don't you wish sometimes you could just shut off your brain, stop thinking, and settle in for a long nap?
ALEX CHADWICK, host:
Well, I'm trying to stay awake through the end of the show.
(Soundbite of laughter)
BRAND: But maybe after? Well, after the show, you might have a lot in common with squirrels this time of year. A lot of squirrels hibernate during the winter. They actually switch off their brain cells for a week or more at a stretch, and now scientists say they're beginning to understand how these squirrels do it and what it might mean for people like Alex.
NPR's Jon Hamilton has more.
JON HAMILTON: Craig Heller is a biologist at Stanford who spent decades studying ground squirrels - think chipmunks without the facial stripes. That's because ground squirrels hibernate. Tree squirrels don't. Heller is especially interested in the Golden-mantled Ground Squirrel. It does more than just shut down its brain during hibernation. The squirrel actually gets rid of many of the biological wires that connect its brain cells.
Professor CRAIG HELLER (Biology, Stanford University): Imagine losing 20 to 40 percent of your neural structure. And then when the animals came out of hibernation, it all comes back in three or four hours. It's the most incredible recovery of neural structure that we know of.
HAMILTON: Heller is part of a team that's been trying to understand precisely what happens to individual brain cells during this process. The team's latest research appears in the Journal of Neuroscience. It shows that soon after a ground squirrel begins hibernating, each brain cell actually gets smaller.
Prof. HELLER: It's like a big bush. And what we're seeing is we're seeing the extent of that bush being retracted.
HAMILTON: It's as if the bushy cells are pulling in their branches all over the brain. The structures that retract form connections with other nerve cells, and it's these connections that let us remember who we are and where to find food. So Heller says it's kind of amazing that most squirrel memories remain intact after hibernation.
Prof. HELLER: They clearly don't forget how to be a squirrel. There are important things that they don't forget. For example, they don't forget who their relatives are.
HAMILTON: Somehow, the squirrels are able to reassemble the vast network in their brains. That suggests the animals are carrying some sort of blueprint that brain cells can use to put everything back the way it was. It's still not clear how that happens. Even so, Heller says it raises a provocative question about humans with brain damage from a stroke or Alzheimer's.
Prof. HELLER: If there were a way to actually repair the loss of structure which results from disease or accident such as a stroke - if there's a way of repairing that, could we get the function back?
HAMILTON: That question won't be answered anytime soon. But it's one that intrigues doctors like Kai Frerichs. He's a neurosurgeon at Brigham and Women's Hospital in Boston. Frerichs says he's especially intrigued by evidence that the ground squirrel's brain has special protection only when the animal is hibernating.
Dr. KAI FRERICHS (Neurosurgeon, Brigham and Women's Hospital): That gives hope that maybe there is something we can learn from this state that could be transferred to a non-hibernating species as well.
HAMILTON: Frerichs says you might be able to help people who've just had a stroke if you could induce a state similar to hibernation. He says right now, brain tissue begins to die almost immediately after a stroke.
Dr. FRERICHS: The more time elapses, the more likely the tissue damage is going to continue and get worse. So if there's anyway we could just calm everything down, that could potentially enhance the chances of having a good outcome.
HAMILTON: Stroke patients might be able to save their brain cells by putting them into a sort of suspended animation for a few days, just like a ground squirrel. Jon Hamilton, NPR News.
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