Short Wave - Scientist Just Made The Largest Brain Map Ever

Episode Date: October 27, 2023

The human brain has more than 170 billion cells. A newly published atlas offers the most detailed maps yet of the location, structure and, in some cases, function of more than 3,000 types of brain cells. The atlas could help scientists understand what makes humans unique in the animal kingdom and the roles different brain cells play in disease. Science correspondent Jon Hamilton talks to host Regina G. Barber about the findings from this new map, a product of the NIH's BRAIN initiative. Plus, what the heck splatter neurons have to do with all of this!Read Jon's full story here. Science question on your brain? Email us at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, Short Wavers, Regina Barber here. Today we're going to talk about maps. But not the kind that you use to drive to that restaurant. Everyone's been talking about. These maps are helping scientists navigate the human brain. So we've summoned NPR's own wannabe brain cartographer, science correspondent John Hamilton. Hey, John.

Hey. What kind of brain maps are we talking about? I mean, do they show where my neuroses live? Not exactly. These maps are part of a new Atlas that shows where to find different types of cells in the brain. That might sound pretty straightforward, but a human brain actually has more than 170 billion cells. Wow. And so far, scientists have identified more than 3,000 different types. Oh, okay.

You know, you have cells that help you wiggle your toes and other types of cells that help you process what you see in here and other ones that even help you ponder things like the nature of consciousness. Like I do. There is a lot to map. And producing this first draft of the Atlas took hundreds of scientists the better part of a decade. Wow. Okay. So obviously somebody thought this was super important. Can you break down how this Atlas is going to be used?

I think I'll let one of the lead scientists on this project do this for me. His name is Ed Lean, and he's at the Allen Institute for Brain Science in Seattle. 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? And it now becomes a really foundational reference for us to think about what happens in disease. Which of these types of cells might be vulnerable in disease?

Today on the show, mapping the brain cells that allow us to walk, talk, and think. Plus, we are going to talk about splatter neurons. I am not making that up. I love that name. You're listening to Shortwave from NPR. Okay, so John, this new brain atlas took hundreds of scientists to map billions of cells. Who was behind this project? This short answer is President Obama.

This all goes back to something called the Brain Initiative that the president unveiled back in the before times, by which, of course, I mean 2013. There's this enormous mystery waiting to be unlocked. And the Brain Initiative will change that by giving scientists the time. 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. I remember that. It sounded pretty ambitious at the time. Yeah, it was. But the brain initiative has really delivered. And one reason is that it invested heavily in the creation of these tools that you need to study something as complex as the brain.

For example, it used to be that scientists might identify a particular cell by studying its shape under a microscope. Or they'd use an electrode to measure its electrical activity. Cool. But the Brain Initiative helped fund technology that could automatically slice up brain tissue, put each slice on a slide, record its location in the brain, and create a digital image that would be interpreted by a computer. It also helped create these tools that let scientists take thousands of cells at the same time

and really quickly figure out which genes are turned on and off in each cell. And, of course, it helped create these huge public databases of brain cell data that any scientists can use for their own research. Okay, so lots of new technology. Was that the key to mapping the human brain? In part, the other thing the brain initiative did really well was it embraced this idea of what people call big science, you know, having hundreds of scientists working together on a single project. So you had all these high-powered teams, and in the past, they would have been competing against each other. But in this case, they all met and they shared data on a regular basis.

And a couple of years ago, I talked to John Nye. He's the scientist at the NIH who is in charge of the brain initiative. And here's how he described the approach. Some problems are so large and complex that it really does require not just a village, but a city or larger, of talented people to really find and build new tools to really get up better solutions. Yeah, but they must have had to test those solutions, right, to make sure they work. How did they do that? Well, on mice. A lot of the early work ever required our little rodent friends.

Right. Something a lot smaller, simpler than the human brain, right? Yeah. And so you're talking about, you know, millions of cells instead of billions. And scientists already knew a lot about the mouse brain and the types of cells that it has. So they were able to see which new approaches work before using them on human brain tissue. But there was still some challenges. One was that you needed living brain cells to do certain kinds of analysis.

That's pretty easy with mice, but, you know, there are some ethical hurdles to clear before you can get living brain cells from a person. I mean, other than taking living brain tissue from somebody who's having, like, brain surgery, I can't think of a possible ethical way to get living brain cell tissue. And in fact, that's exactly what the Alman Institute did. I'm a genius. They formed this partnership with some local brain surgeons. And when a surgeon needed to remove brain tissue from a patient who had, say, a tumor or epilepsy, They would take healthy tissue that they had to remove on the way to the disease tissue, and they would send a portion of it over to the Institute's lab. Of course, these patients had to get permission.

Fortunately, a whole lot of them did. Awesome. Okay. So once the scientists were able to study human brains, what did they find? For one thing, as I mentioned, they found more than 3,000 different types of cells. And this was just in what the scientists are calling a first draft of the Brain Atlas. Wow. Okay.

First edition. Yeah, exactly. They expect to find a lot more as this atlases are refined. Okay, so what do these cell types do? Like, what makes them different? Well, one type of cell that we've all heard of is, of course, the neuron, right? Yes. And in our brains, we have about 86 billion neurons, and they are what we often call the gray matter in our brains. And one defining characteristic of these cells is that they use electrical signals to communicate. But the brain also has about 85 billion cells that are not neurons.

They are called glial cells, and they are a big part of what is known as the brain's white matter. So glial cells don't send electrical signals, but they do send chemical signals in addition to performing a whole bunch of functions that help neurons stay healthy. Then within each of these two big categories of cells, there are lots of subcategories. We've got special neurons called photoreceptors that respond to light, and we've got special glial cells called astrocytes that maintain the blood-brain barrier and provide nutrients to neurons. In the past decade, scientists have identified more and more subtypes. Wow. Okay. This amounts to the creation of this sort of parts list for the brain.

But they're still finding new cells. And a lot of cell types that have been identified, they still don't really know what they do. Ooh, like which ones? Like splatter neurons. Yes. I knew we were going to get back to them eventually. So what do scientists know about these splatter neurons? Well, they know that they're found all over the brain and they have complex shapes, or at least they do when you look at them in three dimensions.

But when they're squashed down into two dimensions, you know, like on a paper map, they look like bugs that have hit your windshield. Like those Rorschach tests. Exactly. Splattered, right? Sadly, that name is probably going to go away when scientists learn more about these cells. Oh, boo. Okay. So, but how is the new brain atlas going to change? change things for scientists and for the rest of us.

It's already providing a new way to see how the human brain is different from animal brains. Turns out we humans have some specialized neurons for processing visual information, and those cell types don't exist in mice. You know, humans mainly process things visually, so it makes sense. Mice depend on their sense of smell. Knowing about that sort of difference is really important if you're using mice to study human diseases, especially since we know mice findings don't always translate into humans. Right. So like what other animals are they looking at? As part of these hat lists, scientists actually map the brain cells of some of our closest relatives, and that includes chimps and gorillas. I talked with one of the researchers involved

in that work. This is Dr. Trigva Bakken of the Allen Institute. One question was, do we have cell types that are unique to humans and not found in chimpanzees, for example? What we found in this study is that there really is a conserved set of cells. cell types that we share with chimpanzees and gorillas, but the gene expression has changed in those cells. So what does it mean that the gene expression has changed? Gene expression is really which genes in a cell are turned on or off at any given time. Right. And in this case, what they found was that even though humans and apes had all the same types of brain cells, these cells were turning on different genes.

So, for instance, in a brain area that humans use for language, cells were turning on genes that were not turned on in apes. And these genes are involved in creating synapses, you know, the connections between neurons. Yeah. So what all this suggests is that human use of language doesn't really require different types of brain cells, just different wiring. Wow. So I guess we're not that special after all. Yeah, I mean, that is kind of the humbling message that we are getting from the world of science. Sad but fair. Okay. So the big thing that's been on my mind this whole time is this going to speed up scientists' ability to research brain diseases? It will. Now that scientists have these maps, they can start looking at which cell types are

affected in conditions like depression or schizophrenia or Alzheimer's. Bingren is at the University of California, San Diego, and he says his team has already learned some things from the Atlas. We found that late-onset Alzheimer's disease are particularly associated with a type of cell we call microglia. These are not neurons. They are cells that carry out the equivalent immune function in the brain. And that is really interesting because scientists already know that these microglia, these immune cells, are activated in areas of the brain that are affected by Alzheimer's. So one question is whether you might be able to slow down Alzheimer's by somehow

controlling these cells. Wow. Thank you for bringing us the story, John. anytime Regina. Before we head out, a quick shout out to our Shortwave Plus listeners. We appreciate you and thank you for being a subscriber. Shortwave Plus helps support our show and if you're a regular listener, we'd love for you to join so you can enjoy the show without sponsor interruptions. Find out more at plus.npr.org slash shortwave. This episode was produced by Burley McCoy and edited by managing producer Rebecca Ramirez.

John Check the Facts. Maggie Luther was our audio engineer. Beth Donovan is our senior director and Anya Grunner. is our senior vice president of programming. I'm Regina Barber. Thank you for listening to Shortwave from NPR.