Song of the Cerebellum

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1:17RebeccaFilm.com slash audio. Wait, you're listening. Okay. All right. Okay. All right. You're listening to Radiolab. Radiolab. From WNYC. Yeah.

1:39Hi, Latif. Hello. All right. So, reporter walks into a bar. Okay. And that's just the beginning of our story. That reporter's name is Rachel Gross. She is 35. The year is 2024. It's a warm spring night. The bar is in Brooklyn and it is called the Branded Saloon. So Branded Saloon is a very gay bar. You know it because there are all these rainbow flags bursting out the front. It's like very, very crowded and loud. She's a regular, shows up there nearly every Thursday to hang out. Like grab some fries, hang out for an hour. But also for karaoke. So that night she made her way to the back room. Got on stage, put in like a Savage Garden song, Crash and Burn, from like my teenage years.

2:26Do you know this one? I don't. Can we pull it up really quick? Okay, Crash and Burn, Savage Garden. Okay.

2:38Okay, we got that. Oh, I do know this song. Oh, okay, yeah. Okay, so you're singing along. And I think it was initially going fine, but it's really at the chorus that just like nothing came out of my mouth. It was just air. Could you almost imitate what happened? Yeah, it goes like, When darkness is upon your door and you feel like you can't take anymore. Is it like when you have a sore throat and suddenly you're just like, oh, I can't, there's nothing coming out? Or did it feel different? No, it was the notes weren't translating from my brain to my vocal cords. And the rest of the song, like the verses, I just felt like I wasn't on the beat.

3:27But you finished it out. You finished out the song. Yeah, I mean, I am used to bombing. It's part of my philosophy of karaoke. It teaches you how to be okay with things not going perfectly. So I was trying to keep that in mind while I was like, damn, what just happened? I literally crashed and burned. And that night when she got home, Rachel started thinking about another moment from the day that was a little strange. I was like shadowing an acupuncturist because I was writing about alternative medicine. I take like handwritten notes and my writing was so poor, I couldn't read it afterwards. So that was another like, hmm, odd.

4:08But Friday, I felt myself to be slurring a bit. And then on Saturday, I decided to go for a run and it felt really weird. It felt like I was like forcing my limbs to run in tandem. And it was after that run that I decided I needed to go to the hospital.

4:37I remember they handed me the form that you just fill out with your basic information. And I couldn't fill out the form. Like, I couldn't write my name and birth date. They do a CT scan. And the PA comes up to me and he's like, honey, you have a bleed in the back of your brain. In other words, she'd had a stroke. And that's when I went into shock. So they rush her across town to a hospital that has a stroke ward. There's like a lot of beeping. Most of the patients are over 70, of course. The neurologist and all her residents come in and they eventually said, we think this is a cavernoma. It's like where very small blood vessels form a little, like, raspberry.

5:23Huh. And this little raspberry can exist your whole life, but sometimes it bursts. And that's when you have a stroke. And in my case, doctors were saying, you should probably have surgery to remove it. And where exactly in the brain was the stroke? In the cerebellum. And where is that? What is that? I didn't know what the cerebellum was at that point. But the neurosurgeons told me that it's in the back of my head, basically behind my neck, and it's involved in fine-tuning motor stuff. They also called it redundant. Redundant. And later, one of them called it practically vestigial. It almost sounds like an appendix.

6:05Yeah, exactly, exactly. Another one said, because I was terrified about surgery, obviously, he says you can actually take out a third of it. and people don't even notice. He was like, when you wake up, you might feel a little bit clumsy, but you'll still be you. Huh. Was it kind of like this is of a place to have a brain situation, the cerebellum's a lucky spot? Yes. Yes, that was definitely, definitely reassuring. So Rachel went into surgery. They removed a piece of her cerebellum. And then when she woke up, she started, like, testing herself. And so I drew a spiral and it was smooth and it didn't tremor or whatever.

6:48Within a few more days, I was like circling the hall by myself and nurses were like clapping for me. So I was like, I'm going to have the best recovery they've ever seen. So you're like writing, check, walking, check. Yeah, yeah, yeah. Like stuff's coming back. You're like, yeah. But over the next couple of months. I could just still hear that slur so much. It bothered me so much. and I tried singing along to a couple of karaoke tracks and I couldn't get the timing right, let alone the notes. But then the other experience I was having was a sentence that I want to say will just kind of disappear or escape me and I will laugh at something but it'll come out like too big or too like rambunctious.

7:37It felt much more profound than you're having some body coordination issues. That's like kind of what I'm trying to figure out now. So Rachel Gross is actually a science journalist, and she writes a lot really beautifully about the body. Right. Yeah, yeah, yeah. I know her work. Yeah, she wrote this awesome book called Vagina Obscura. Terrific book. And so when she told me she wanted to talk, I figured she was going to tell me a story full of fun facts about this other body part. But as we sat there talking. And I need to just go for the nearest word. It became clear she was in the middle of a story.

8:17That's a difficult thing to accept for someone who's like used to writing precisely. It was still unfolding. There's this confrontation with your sense of like who you think you are. So I guess like, what do you really want to know? what are you after? What do you want to find out? I think the simple quest is I want to figure out how to get my karaoke back. But that's not the bigger thing. I think my question now is, why does this feel like more than just a motor problem, more than just fine-tuning? Why do I not feel like myself anymore?

9:04So after that conversation, Rachel just started digging and researching, talking to so many people, reading so many studies. Producer Sindhu Nyana Sambandan and I joined whenever we could. And what Rachel discovered is something I thought we were done finding, which is something totally new about the basic anatomy of the brain. and a shift in how we think not just about this part of the brain, but really about thinking itself.

9:38All right. Okay. This is Radiolab. Here we go. Here we go. Okay. So I started in kind of the most obvious place. What do we know about the cerebellum? So cerebellum is the old Latin term for little brain. Little brain. Okay. And it's tucked in under the big brain, sitting in the back of the brain. So I ended up calling this scientist named Jeremy Schmaman. I'm a neurologist at Mass General Hospital. He's been studying the cerebellum for decades now. His whole career. Yeah. So can we just back up and like, what does it look like? Well, it's smaller than the rest of the brain in terms of size. It's about the size of your fist.

10:20But it's very deeply folded. So unlike the big folds of the cerebral hemispheres, everybody knows those pictures, the cerebellum has multiple tiny little folds. And it even lives in its own membrane pocket. So it really looks like a little brain underneath the big brain. And the cerebellum was described in 1776 in terms of its structures by this fellow called Malacharni. And then some 50 years later, people start to look at what cerebellum does. So by the 1800s and early 1900s, scientists are doing these experiments where they basically remove the cerebellum from pigeons and cats or whatever, just to see what happens.

11:02But then in World War I, you actually end up with this massive, unintentional human experiment because of the helmets that the British soldiers were wearing. So maybe you've seen pictures of this, but these helmets, they sit up at the top of the head, kind of like an upside down bedpan. Yeah. And they essentially leave the whole back of the neck exposed, right where the cerebellum is. I see. And the doctors who were fixing up these soldiers noticed that all of them sort of had the same problem. They would stumble around when they tried to walk. They were really jerky. They would fumble when they tried to reach out and grab for something.

11:40In other words, they had... difficulty with the coordination and the timing of the movement. So at this point, science basically concludes... Oh, this is all about motor control. What the cerebellum is doing is all the stuff in the background that you don't even think about when you're moving around in the world. That's correct. And that fits really neatly into the map that we were starting to make of the entire brain, where there's kind of this upstairs part, the cerebrum, which is where like poetry and art and math and all the things that make us human are happening. And then you have sort of the downstairs, the basement, where we're just sort of doing basic body stuff, animal stuff, like movements, breathing and heart rate.

12:27And of course, what science is interested in is all of that thinky human stuff, to the point that even today, if you look at most neuroscience papers that say that they're exploring the whole brain, they tend to just ignore the cerebellum completely. Wow, really? They literally crop it out of their findings. There are MRI machines that don't cover the cerebellum. That's crazy. Yeah, and that's probably why all the surgeons I was talking to when I had my stroke were telling me not to worry. The cerebellum is really just making you less clumsy, and it's really not going to be a big deal if we take a little bit out.

13:07Well, almost everything that you've told me was the understanding of the doctors that you've spoken to is outmoded, outfashioned, and predominantly incorrect. Where we are now is a complete paradigm shift. There's been a revolution in our thinking about the cerebellum. And can we just back up to where that shift started for you personally? As a resident in the neurological unit of Boston City Hospital. This was in 1982. I saw a patient with a stroke in the basal ganglia. And what's the, remind me, what's the basal ganglia? Yeah, the basal ganglia are these structures that are deep in the brain.

13:43And just like the cerebellum, they've been associated with motor control. But this patient wasn't aware of the left side of space. He was having problems with his perception. And that's a syndrome that had been exclusively described in people who have damage to the cerebral hemisphere. Like the upstairs thinky brain. So my question was, well, if this motor system can produce a cognitive change, what about the big motor system downstairs? What about the cerebellum? So I had to go back into the stacks of Harvard Medical School's Countway Library. So he's there in the dusty stacks, and he's pouring through papers for any little footnote or mention of the cerebellum.

14:22And he found this subterranean kind of hidden description of cerebellar damage in people whose behaviors were a little off the beaten track, whether it was mental or emotional or cognitive. But it really got hidden in the literature. Everybody knew that the cerebellum controlled motive function. And one of the people I came across in my reporting was a scientist named Henrietta Leiner. And that was it, motor function. They're still teaching that, I think. This is an interview of her talking about the cerebellum before she died. When I first proposed the hypothesis about the cerebellum. She'd been arguing that the cerebellum was actually influencing cognitive functions in the upstairs brain.

15:09The reviewer, the peer reviewer of the paper, turned it down with a comment, this couldn't possibly be true or we would have thought of it long ago. But, you know, science gets driven by people who have powerful influence. And those folks who were saying this is motor control won the day. And you, I guess, did you start to look into that? What was your next step? So we started looking at the anatomy of how the upstairs brain talks to the downstairs brain. Jeremy figured that if the cerebellum is doing more than just motor stuff, then there would need to be some sort of like infrastructure between the two.

15:49In other words, does the cerebellum have access to information that is beyond motor control information?

16:00So Jeremy and his mentor, Dr. Pagna, this was in the late 80s, they took rhesus monkeys and injected their cerebrums, or the upstairs brain, with these dyes that act like tracers. Tracers that get picked up by the nerve cell. Then they left up the monkeys for a week or so, just going about their day, thinking monkey thoughts. And meanwhile, these dyes travel down the nerve and they end at the point where the nerve ends. And what Jeremy ends up seeing is these lit up highways going down to the cerebellum. From areas of the brain relevant for executive control functions in the frontal lobe, awareness of ourselves in the environment, parietal lobe, temporal lobe involved in language processing, for emotional modulation.

16:46Am I getting too sciency? No, we love it. It's called Radiolab, you know? So all those areas send information into the cerebellum. And then other investigators showed that the cerebellum sends information back up to the thinking brain. So now in a word, you have an anatomical circuitry linking cerebellum to the thinking brain. Wow. Yeah. the neocortex and the cerebellum are massively interconnected. And according to evolutionary biologist Robert Barton at Durham University in the UK, there seems to be a very particular evolutionary relationship between these two structures. These connections between the thinky brain and the motor brain might actually be a big part of the story of how humans became humans.

17:38One of the really popular ideas about brain evolution is predominantly a story of the expansion of the cortex. But we made two discoveries that kind of started to challenge that conventional wisdom. So what he and his colleagues did was gather up a bunch of data about the size and the structure of the brains of a bunch of different primates. And then if you know how those species are related to each other, you can reconstruct patterns of evolutionary change. So the first thing Robert notices is that... Across all of the primates... Their cerebrums and cerebellums are evolving in lockstep. They're pretty tightly coordinated.

18:23But then we stumbled on a pattern in the data that took me by surprise, which was that when we get to the apes, the ape part of the story, we see a deviation from that general pattern of coordinated evolution. What we see in the apes is an acceleration in the expansion of the cerebellum. Wait, so you're saying like the cortex got bigger, but the cerebellum... It got big faster. Wow. Kind of outstripping it. So what Robert is really saying here is that right at the moment that we are becoming human, which everyone has assumed was all about the upstairs brain, it was actually the cerebellum, so the lower brain, that was rising to the moment.

19:09Yeah, exactly. To the point where in the human brain today... Although it's a lot smaller than the neocortex, it has about four times more neurons. What? That's a lot! Isn't that bonkers? The cerebellum has about 80 % of the brain cells that we have. Wait, 80 % of the brain cells of our whole brain are in the cerebellum? Right. There's a lot of brain in there. And that's the part they cropped out of the MRIs or whatever? Exactly. Exactly. But here's the thing that's remarkable. Most of the cerebellum, in terms of the size of cerebellum, is the region that is interconnected with thinking brain, not motor brain.

19:50Wow. Most of the human cerebellum has nothing to do with motor control.

19:58So to collect what we have here, there are old case studies where people with cerebellum injuries, it's more than just a motor problem. Ape and human cerebellums are bigger than other primate cerebellums. Exactly. Right. And it's massively connected to the rest of the brain. To the thinky parts. Yeah. Okay, so I still do not understand what is this thing even doing? I mean, that's the 80 million neuron question or the 80 billion neuron question.

20:32And we will get to that right after this break.

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23:11Okay, Latif. Lulu. Radiolab. We are back talking about the cerebellum, this little part of the brain down near the neck that for a long time was believed to be distinctly about motor stuff, smoothing walking, smoothing handwriting, until very recently scientists began noticing that this part of the downstairs brain was wired up to the big brain upstairs, where, you know, all kinds of behaviors like speech and decision-making and emotional regulation are processed. Right, right. But the question for Jeremy Schmamman at this point is, what is it actually doing? And I remember presenting the anatomy of this story at one of the neuroscience meetings.

23:52And a well-meaning senior colleague said, you're telling us that the Shrebelam's involved in behavior. Well, what kinds of behavior? And I really couldn't answer the question. I wasn't sure. So we did what we do in clinical neuroscience. We went to the patient, and I met a young woman in her early 20s. She had slipped on some ice and fallen backwards and hit her head. It was just a slip and fall, but she had a CAT scan, and they found a tumor in the midline of the cerebellum. Oh, my gosh. The tumor was taken out, and she did fine from the motor perspective. But what was noted right from the get-go by the nurses in the ward is that she had difficulty coming up with words or using words correctly.

24:42She had difficulty with planning and organizing her thoughts. And she'd had a change in her personality. Like what kind of change? She was being disinhibited. She was just robing in the corridor. She was being rude to her parents. She was hiding under the bed covers. She was talking in a high-pitched kind of whiny tone of voice, which was a change for her. But this came from cerebellar damage. The brain upstairs was fine. And we then... Since then, he's had dozens more patients. Who'd had cerebellar-focused damage. And they all have different problems with their motor and cognitive and behavioral skills.