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ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

In 2013, President Obama put brain science on the national agenda. And today, we're going to look at some of the things his BRAIN initiative is trying to accomplish. Back in April, the president said one his goals was to help scientists whose research is being held back by technical obstacles.

PRESIDENT BARACK OBAMA: The BRAIN Initiative will change that by giving scientists the tools they need to get a dynamic picture of the brain in action and better understand how we think and how we learn and how we remember.

SIEGEL: NPR's Jon Hamilton reports on one of those tools that could help reveal the brain's secrets.

JON HAMIILTON, BYLINE: Studying the brain is a bit like studying a computer. You can't really understand how it works unless it's switched on and doing something. Elizabeth Hillman of Columbia University says that presents a big challenge for brain researchers.

ELIZABETH HILLMAN: If it has to be switched on and it has to be intact, how on Earth do you get the information out? We need tools. And I mean, really, that's the message of the BRAIN initiative.

HAMIILTON: Hillman says tools like fMRI scans can offer a glimpse of which brain cells are active during a task. And you can manipulate individual cells by placing wires in the brain, though that's usually limited to certain patients awaiting brain surgery. But until recently, Hillman says, there was no good way to study a specific type of brain cell in action or to tweak whole networks of cells. Hillman says all that changed in 2005, when a team at Stanford showed how to control brain cells using light.

HILLMAN: There was instant buzz about it. People were sort of running around and saying, what is this thing? Where can I get it? How can I do it? You know, this is fantastic.

HAMIILTON: The technique is called optogenetics. And Hillman says it provides a way to switch cells on and off in a living, functioning brain.

HILLMAN: Now you can select that very specific genetic cell type. And you can tell that specific cell type to react when you shine light on it.

HAMIILTON: So if you select the right type of motor neuron in a mouse, you can make the mouse start running with the flick of a light switch. It's also possible to control brain cells involved in pain and fear and moods. So there's huge potential for both understanding the human brain and treating brain diseases.

But Hillman says optogenetics is facing some big challenges before it's ready for people.

HILLMAN: So the first challenge, of course, is that you're actually altering the genes of the neurons.

HAMIILTON: That's because most neurons don't normally respond to light. So you have to add genetic material to every brain cell you want to control. Scientists can do that in mice with genetic engineering but that's not an option for people. The other way to add genetic material is by infecting an animal with a virus that reprograms certain cells. Hillman says this approach has been used in people, but carries risks that probably mean most human optogenetic experiments are a long way off.

Hillman says another challenge for optogenetics is delivering light to cells deep in the brain. She says it's easy to illuminate cells near the surface.

HILLMAN: There, we can do anything. We are the magicians of the superficial layers of the cortex. We can turn things on, turn things off, read stuff out. That's fine.

HAMIILTON: But she says it's a different story in the layers below.

HILLMAN: It's really hard to get light to go deep. And we all know this just from trying to sort of shine a flashlight through our hand, you know, you really don't see a lot of light coming through tissue.

HAMIILTON: Hillman spoke about that challenge at a BRAIN Initiative meeting this month at the Optical Society of America.

Another speaker was Hillel Adesnik from the University of California, Berkeley. He says a different problem occurs when light reaches too many cells in the brain.

HILLEL ADESNIK: If you want to say what is one of the major caveats of optogenetics, is that it's like slamming the thing with a hammer.

HAMIILTON: So Adesnik says scientists are looking for ways to deliver light with less force and more precision.

ADESNIK: One thing that's been very much discussed is how we can control the cells one at a time, or 10 at a time, or a thousand at a time, but extremely specifically.

HAMIILTON: Adesnik says you can see the potential of optogenetics if you look at its impact on a specific brain disorder, like epilepsy. Scientists know that epileptic seizures occur when brain cells start firing out of control. But Adesnik says they've been struggling to understand the role of so-called inhibitory neurons, which quiet down other brain cells.

ADESNIK: Prior to optogenetics, there was no way to control these neurons and test hypotheses.

HAMIILTON: Now, Adesnik says, there is - at least in mice.

ADESNIK: You can manipulate the activity of this inhibitory class of cell and either stop a seizure or, if you're studying epilepsy, per se, to initiate a seizure.

HAMIILTON: Adesnik says some day it may be possible to halt a person's epileptic seizure with a flash of light. And by tweaking other networks in the brain, he says, doctors may be able to help people with Parkinson's disease, depression or even schizophrenia.

Jon Hamilton, NPR News.

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