MARY LOUISE KELLY, HOST:
Scientists are one step closer to understanding the human brain. NPR's Jon Hamilton reports on a new atlas cataloging more than 170 billion brain cells, cells that allow us to walk, talk and think.
JON HAMILTON, BYLINE: The atlas arrived in the form of more than 20 research papers in three different scientific journals. Together, the papers map out the location, structure and function of at least 3,000 types of brain cells. Ed Lein of the Allen Institute for Brain Science is one of several hundred researchers who worked on the project.
ED LEIN: We really need this kind of information if we're going to understand what makes us unique as humans or what makes us different as individuals, or how does the brain develop.
HAMILTON: Lein says the atlas also offers a way to study conditions ranging from Alzheimer's to depression.
LEIN: You can use this map to understand what actually happens in disease and what kinds of cells may be vulnerable or affected.
HAMILTON: The atlas still isn't finished. Researchers expect to find even more types of cells, and they don't fully understand some of the ones they've already found, like splatter neurons. Lein says the name describes what these highly complex cells look like when they're represented in two dimensions instead of three.
LEIN: When you do that with these types of neurons, it looks a bit like a Rorschach test. It's a splatter of these types of cells.
HAMILTON: Like bugs on a windshield. Lein says the atlas in its current form amounts to a first draft.
LEIN: But it really has set the stage to show that this is a definable system.
HAMILTON: And already, the atlas is offering a way to see how the human brain differs from animal brains. Dr. Trygve Bakken of the Allen Institute says humans have some specialized cells for processing visual information that mice don't.
TRYGVE BAKKEN: We share kind of a basic plan with mice, but we see specializations in primates that we don't necessarily see in a mouse.
HAMILTON: Those specializations are present in primates like chimps and gorillas, whose brains were also mapped as part of the atlas project. But Bakken says in those species, scientists found subtle differences in the brain areas that humans use to process language.
BAKKEN: What we found in this study is that there really is a conserved set of cell types that we share with chimpanzees and gorillas, but the gene expression has changed in those cells.
HAMILTON: In ways that suggest humans' language abilities are the result of a different wiring, not different brain cells. The atlas project is funded largely by the National Institutes of Health as part of its BRAIN Initiative, which was launched a decade ago by President Obama. One of its goals is to find new treatments for brain disorders. Bing Ren of the University of California San Diego says these disorders often occur when our DNA undergoes subtle changes.
BING REN: Interpreting those changes actually has been the hard part because we lacked the dictionary to understand what they are.
HAMILTON: So as part of the atlas project, Ren and his team have been creating a dictionary that links genetic changes to specific types of brain cells.
REN: For example, we found that late-onset Alzheimer's disease are particularly associated with a type of cell we call microglia.
HAMILTON: An immune cell that's known to be activated in Alzheimer's patients. Ren says the dictionary also connected genes that raise the risk of major depressive disorder with one particular set of neurons.
REN: By contrast, a different set of neurons are being linked to the risk of schizophrenia.
HAMILTON: Ren says this sort of information could lead to treatments that target specific types of cells. The new research papers appear in the journals Science, Science Advances and Science Translational Medicine. Jon Hamilton, NPR News.
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