DAVID GREENE, HOST:
Scientists have taken one more small step toward understanding what makes the human brain unique. As NPR's Jon Hamilton reports, they've identified a type of brain cell that exists in people but not in rodents.
JON HAMILTON, BYLINE: The cells are called rosehip neurons, and they were first described by a scientist in Hungary named Gabor Tamas. Ed Lein of the Allen Institute for Brain Science in Seattle says Tamas was recording electrical signals from cells taken from two human brains.
ED LEIN: In the course of doing these recordings, he started to notice a very distinctive type of cell that to him had the shape of a rose after the petals have fallen off. So he called them the rosehip cell.
HAMILTON: Meanwhile, Lein and other scientists at the Allen Institute had also run across these unusual neurons while doing a genetic analysis of the brain cells. So the researchers combined what they had learned. And Lein says their conclusion was remarkable.
LEIN: This particular type of cell had properties that had never actually been described in another species to date.
HAMILTON: The findings suggest that the human brain is more than just a big mouse brain. At some point, it acquired at least one kind of cell a mouse doesn't have. Scientists aren't sure exactly what these cells do, though they seem to be involved in controlling the flow of information in the brain. And Lein says their existence has big implications for researchers.
LEIN: It throws some doubt on the ability to use the mouse, then, to study certain elements of human function and disease.
HAMILTON: Rosehip cells are a type of inhibitory neuron. They act like the brakes in a car telling other brain cells when to slow down. And Lein says it's possible they play a role in mental illness.
LEIN: These types of cells are extremely important. And dysfunction of them can actually directly be linked to different types of neuropsychiatric disease like schizophrenia.
HAMILTON: If rosehip cells are involved in brain disorders, it could help explain why so many brain drugs that work in mice don't work in people. Josh Gordon directs the National Institute of Mental Health, which helped fund the research.
JOSHUA GORDON: It may be that in order to fully understand psychiatric disorders, we need to get access to these special types of neurons that exist only in humans.
HAMILTON: Gordon says this study is part of a larger effort by the National Institutes of Health to identify every type of cell found in the brains of mice, monkeys and people.
GORDON: We don't know how the brain works if we don't know all of its parts. Right? So in order to describe how the brain produces behavior, we want to know what are the different parts in the brain and then how they work together.
HAMILTON: New genetic techniques are rapidly improving scientists' ability to detect new types of brain cells. And Gordon expects that researchers will find more cells that exist in people but not animals.
GORDON: I think it's very, very likely that this is the tip of the iceberg.
HAMILTON: The new research appears in the journal Nature Neuroscience. Jon Hamilton, NPR News.
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