ARI SHAPIRO, HOST:
Researchers have created a new, highly detailed map of the human brain. This map doesn't feature the brain's anatomy. It shows which genes are expressed in different areas. NPR's Jon Hamilton reports it provides some hints about what makes the human brain special.
JON HAMILTON, BYLINE: Scientists have been dissecting human brains for centuries. But Ed Lein of the Allen Institute for Brain Science in Seattle says they still haven't explained abilities like using language or solving complex problems.
ED LEIN: Clearly, we have a much bigger behavioral repertoire and cognitive abilities that are not seen in other animals, but it's really not clear what elements of the brain are responsible for these differences.
HAMILTON: So Lein and a team of researchers have been looking at which genes are expressed or switched on in different areas of the brain. They studied brains from six typical people. Lein says usually this sort of study asks about differences across the brains.
LEIN: And we sort of flip this question on its head. And we asked, instead, you know, what's really common across all individuals, and what elements of this seem to be unique to the human brain versus being more general to all mammals, let's say?
HAMILTON: And it turned out the six brains had a lot in common. Mike Hawrylycz of the Allen Institute is lead author of the paper which appears in Nature Neuroscience
MIKE HAWRYLYCZ: One of the big findings of the paper is that whereas there's a lot of very, very small variation on a grand scale in the brain, there's only a limited number of patterns that these genes take.
HAMILTON: The team identified 32 of the most common genetic expression patterns. Then they compared the patterns in people with those in mice. And they found something that could help explain what makes human brains so different. Ed Lein says it involves neurons and another type of brain cell called the glial cell.
LEIN: The patterns that are more related to the neurons, the sort of information carriers in the brain, tend to be better conserved across species, whereas those that are related to the support cells, the glial cells, are actually less conserved. This is somewhat of a surprise.
HAMILTON: A surprise because scientists used to think glial cells weren't involved in higher brain functions like thought. But recent studies have suggested that glial cells, and especially a star-shaped variant called astrocytes, play an important role in learning and intelligence. Ben Barres is a professor of neurobiology at Stanford University.
BEN BARRES: We've spent a lot of years studying the function of glial cells using the mouse brain as a model system. And we've actually found, to our great surprise, that the glial cells are actually much more active in controlling neural circuits in the brain than people have generally thought.
HAMILTON: Barres says research in his lab has shown that astrocytes help determine where and when neurons make connections in the mouse brain. And he's begun studying astrocytes in the human brain, but he says that's difficult.
BARRES: It's actually very hard to get human brain material that's in sufficiently good condition to study it. And so as soon as the tissue is removed from the body, it starts to degrade.
HAMILTON: Barres thinks scientists will find out precisely what makes a human brain different, but he says they may have to employ a new technique. It uses stem cells to grow miniature human brains in the lab.
There's one more thing the new research turned up. It's a possible explanation why so many brain drugs that work in mice don't help people. Mike Hawrylycz of the Allen Institute says that among the genes that varied the least in those six human brains were those associated with diseases such as epilepsy, autism and Alzheimer's. So Hawrylycz says they looked for these same patterns in mice.
HAWRYLYCZ: And it turns out that the patterns which are typically most associated with some of these diseases are not really well recapitulated in the mouse.
HAMILTON: The mouse brains didn't have those gene patterns. So future drug testing may include those miniature human brains grown in the lab. Jon Hamilton, NPR News.
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