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DON GONYEA, HOST:

It's MORNING EDITION from NPR News. I'm Don Gonyea. For President Obama, 2013 wasn't just the year of Obamacare. It was also the year of the brain. Here he is announcing his BRAIN initiative back in April.

(SOUNDBITE OF SPEECH)

PRESIDENT BARACK OBAMA: You know, as humans we can identify galaxies light years away. We can study particles smaller than an atom. But we still haven't unlocked the mystery of the three pounds of matter that sits between our ears.

GONYEA: NPR's Jon Hamilton reports that the president's plan to figure out the human brain is starting with a lot of research on mice and fruit flies.

JON HAMILTON, BYLINE: A person's brain has about 100 billion neurons. The brain of a fruit fly has only about 100,000. But Rachel Wilson at Harvard says you can learn a lot from a brain smaller than a poppy seed. For example, she says, fruit flies are helping to explain a problem that affects many people with autism.

RACHEL WILSON: And that's the problem of volume control.

HAMILTON: Wilson, who presented her work at this year's Society for Neuroscience meeting, says many people with autism are overwhelmed by loud sounds, bright lights, strong odors, or simply being touched. The reason appears to be a malfunction in brain circuits that adjust the volume of sensory signals from our eyes, ears, nose, and skin. Wilson says this built-in volume control is what allows the human brain to process signals that range from very strong to very weak.

WILSON: So the softest sound you can perceive versus. the sound of a jackhammer, those sounds vary in terms of their physical energy by something like 10 orders of magnitude. Similarly, odors turn out to vary over a really huge range in terms of the lowest concentration of an odor you can perceive versus the most intense odor that you can smell.

HAMILTON: Wilson says a fruit fly also can perceive a wide range of odors and also uses a volume control system in its brain. She thought if she could figure out how the system worked, it might help explain why many people with autism experience sensory overload.

So Wilson and her team did a series of experiments on fruit flies. And they discovered special brain circuits that constantly adjust a fly's sensitivity to odor signals. She says the circuits work a bit like the gas and brake pedals in a car.

WILSON: So when signals are barely detectable, the gas dominates. And that's probably useful because it boosts the sensitivity of the whole system. But when odors are intense, when volume control is really needed to turn down the volume, then it's the brakes that dominate.

HAMILTON: Wilson suspects those same circuits are faulty in people with autism. Of course, fruit flies are best for studying basic functions in the human brain. For more complicated stuff scientists need more complicated animals, like mice. Joshua Trachtenberg at UCLA says mice are helping him figure out how children learn to see the world in three dimensions.

JOSHUA TRACHTENBERG: You don't initially have very good three-dimensional vision and this three dimensional vision emerges during the first two years of life or so.

HAMILTON: That's when the brain learns to combine the information from our two eyes to give us depth perception. Children who have crossed eyes or other vision problems that aren't corrected usually don't develop this three-dimensional view of the world. Trachtenberg says that's because there are critical periods during childhood in which the brain is able to learn things it can't later on.

TRACHTENBERG: The part of the brain that seems to be most affected during these critical periods is the cortex. So we need an animal that has a cortex and the mouse is great.

HAMILTON: Trachtenberg was part of a team that used mice to identify a group of cells in the cortex that determine the brain's ability to acquire 3-D vision. He says the team also found a way to control these cells with drugs. So in one experiment, he says, they were able to take young mice and switch off this visual learning, also called plasticity.

TRACHTENBERG: But more importantly, we were able to go to fully adult animals that don't normally have this kind of plasticity and turn it back on. So we were basically able to make the adult brain of a mouse resemble, in terms of plasticity, a juvenile brain.

HAMILTON: Trachtenberg says that means it should be possible to give people who never developed 3-D vision a second chance to acquire it. And he says this ability to return areas of the brain to a youthful learning state could be useful in treating a wide range of other brain development problems, from ADHD to perhaps even schizophrenia.

TRACHTENBERG: And that's really the goal of the BRAIN Initiative, is to try and understand the brain to begin with and once we understand it on this most basic level we can then go in hopefully and find handles in there that we can use to manipulate the system to make the lives of people better.

HAMILTON: To achieve that goal, though, will require a lot more research on the brains of mice and fruit flies. Jon Hamilton, NPR News.

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