Yasmin Saplakolu (2:18)

People had difficulty with accepting it. It was kind of scary. People were confused by it. Some thought of it as like the devil's number. It challenged, like, really deeply held ideas. And, you know, because of the influence of the church, like philosophers and theologians, associated nothing with, like, chaos and disorder.

Regina Barber (2:39)

One city, Florence, Italy, actually built, banned the number zero altogether.

Yasmin Saplakolu (2:44)

It's a weird concept if you even think too deeply about it. It's like we're describing something that doesn't exist, right? We see three chairs or we see four birds, and we can count those and they're physically there. But we don't see zero birds or zero chairs. We just know that they're absent. But that is zero. That's, you know, an extra level of abstraction from the other kinds of numbers that we see around us all the time.

Regina Barber (3:15)

And that abstraction actually makes it harder for our brains to process. So today on the show the Neuroscience of the number 0. How do humans think about the concept of nothing? How do we find out? And what does that mean for our brains? You're listening to Shortwave, the science podcast from npr.

Yasmin Saplakolu (3:41)

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In celebration of her 50th anniversary hosting FRESH AIR, Terry Gross will be a guest on the Late show with Stephen Colbert. Tune in on Thursday, January 8th on CBS. This holiday season, the team at up first is still hard at work with all new episodes, but but the news does not take a holiday, and we know it's harder than ever to keep up this time of year. Listen for three essential stories in under 15 minutes. Get caught up and get on with your day. Up first, listen on the NPR app or wherever you get your podcasts. Okay, Yasmin, before we get into, like, the complexity of zero, let's just start with, like, the neuroscience of numbers in general. You've done some writing about this, like how our brains comprehend small numbers and differently than large numbers. Can you tell us more about that?

Yasmin Saplakolu (5:05)

Right. So this is actually kind of cool. We have what are called number neurons in the brain. So there are neurons that are tuned to specific numbers. There are neurons that favor, for example, the number five. And there are other neurons that favor the number seven and so on. So that means that for the neurons that favor the number five, they'll fire, morph. Like if it sees five items on a table, it'll fire more than if it sees four or six, it'll still fire for four and six, but less and then even less for three and seven.

Regina Barber (5:41)

Yeah. So these neurons are specifically for that number. They really like that number.

Yasmin Saplakolu (5:46)

Yeah it's kind of neat that we have all of these, and there's a lot of questions surrounding it still. We don't know if there are neurons that fire for, like, a thousand fire. 505. That seems like there would be a lot of neurons in the brain then for the various numbers. I'm sure there's some other kind of mechanism there. And, yeah, there was this research recently that found that the brain actually analyzes small numbers different than it does larger numbers. So there's a weird boundary around the number four. There seems to be some sort of double mechanism that's happening. So the brain processes numbers that are smaller than four in a more precise way than it does for numbers larger than four.

Regina Barber (6:34)

Yeah. Yeah. We did an episode about this, like, way back at the beginning of last year, and, like, how if you get above 4, you're not counting, you're actually comparing. And when you're below four, that's when you're literally like, your brain is counting.

Yasmin Saplakolu (6:46)

Yeah.

Regina Barber (6:46)

So you're not counting anymore past four.

Yasmin Saplakolu (6:48)

So Interesting. Right. It's like, I think about this all the time where it's like, why is it four? Like, why not five? But it's four. And when I reported that piece, a couple of experts were talking to me about how it's also weirdly related to working memory or awareness. So people can only really hold a certain number of objects in their awareness, and that's four. So they think that maybe there's some sort of connection there between, you know, how we're processing numbers and working memory.

Regina Barber (7:22)

Yeah, it's like phone numbers. Right. We're in chunks of three and four for us to remember. Same with Social Security number and stuff like that.

Yasmin Saplakolu (7:31)

Right.

Regina Barber (7:32)

So fairly recently, these two researchers were like, hey, if zero is special in math and history, maybe. And this is what you were saying. Maybe it's special in neuroscience. Maybe we think about it differently. One group looked at patients with epilepsy. They already had these electrodes in their brain, so the researchers were able to see how individual neurons were firing.

Yasmin Saplakolu (7:53)

And the other one, the other group looked more at populations of neurons, so it was kind of a larger scale. They used a magneto. I'm gonna botch this. They used a magnetoencephalography scanner.

Regina Barber (8:09)

That sounds right. That was impressive.

Yasmin Saplakolu (8:11)

Long word. And basically, that means that as the neurons fire, they generate voltages, which creates magnetic fields that the machine can detect. And by analyzing the magnetic fields, the researchers were able to kind of probe what the neurons were doing. When the participants were prompted to Think about zero. That's so cool. Yeah.

Regina Barber (8:33)

So these researchers, they're looking at neurons either specifically or as a group, you know, firing. What did they find? Was there like a new discovery on how we think about zero?

Yasmin Saplakolu (8:44)

So they actually, they were looking for something called the numerical distance effect, which is basically a phenomenon that occurs when the brain processes non zero numbers. And it means that it can more easily distinguish numbers that are far apart from each other than those that are close together. So the brain has a little bit more difficulty distinguishing between like 7 and 8 versus 7 and 10, for example, or 7 and 11.

Regina Barber (9:11)

Got it. Okay.

Yasmin Saplakolu (9:12)

So the idea for both these groups was that we should see if 0 also is part of this numerical distance effect, because if it is, then the brain might be seeing zero just as it does the other numbers. Just a normal number.

Regina Barber (9:27)

Just a normal number. Yeah. Yeah. Probably not.

Yasmin Saplakolu (9:30)

Kinda what happened.

Regina Barber (9:33)

Yeah.

Yasmin Saplakolu (9:33)

So the first group, the one that looked at a bigger scale foundation that the brain processes zero similarly to other numbers. Basically, it puts zero at the start of a mental number line like it's before one.

Regina Barber (9:48)

Excellent.

Yasmin Saplakolu (9:49)

It showed the numerical distance effect, which is what they were looking for. So their conclusion was there's no difference in the way that the brain sees 0 than the other numbers 0 in terms of both the digit 0 and 0 objects. The second group also found that the brain puts 0 before 1 on the mental number line. But they found subtle differences that still made zero special in the brain.

Regina Barber (10:19)

Okay.

Yasmin Saplakolu (10:19)

So, for example, they found that more neurons had zero as their preferred number than other small numbers. That suggested to them that the brain might be representing, you know, this empty set with more accuracy than it does for other small quantities. But this was only true for quantity 0. For the digit 0. They did not find any difference. Like, the brain saw the digit 0 like it does the other digits, like 1, 2, 3.

Regina Barber (10:49)

So in as you're doing this reporting, do you find that these, like, these conclusions are complementary? Do you think that they're, like, fighting each other? What do you think?

Yasmin Saplakolu (10:58)

Yeah, so I actually, it was funny because I had both groups kind of look at each other's results and I was like, what's going on here? Why is this slightly different? And they both said that they think, you know, their results are complementary, actually. And the reason for the discrepancy was most likely just scale. And, you know, they're hopeful that future experiments will be able to kind of tease apart, you know, what the nuances of this are.

Regina Barber (11:25)

So, like, what other, like, research did they. Did the researchers talk about like, that they would like to do.

Yasmin Saplakolu (11:32)

Yeah, I think that, I mean, there's a lot of directions you can go from here. Like, it's how the brain comprehends zero. This was kind of the first step into that. And now, you know, one of the groups, actually, they're hoping to go more in the direction of understanding how the brain comprehends absence, because they think that if they can kind of compare how the brain is processing zero and processing absence, they might be able to see how, like, evolutionarily how the steps toward understanding zero happen. And then the other group, they're more interested in the numbers aspect of things. So they are hoping to look more into some of these maybe stranger numbers. But for example, like, no one looked at the written word zero, which would be a really interesting thing to look at to, like, would that look different in the brain than the digit 0 or than it would for empty sex? Right.

Regina Barber (12:30)

What did you take away from this reporting? Like, you're working on this, you're learning about zero and the history. What was your big takeaway when you're talking to all of these researchers?

Yasmin Saplakolu (12:40)

I think my big takeaway is how incredible and complicated and big the brain is. I just, I think my mind is still blown that we have neurons that are attuned to specific numbers and ways to comprehend these abstract, you know, ideas. Because numbers, and 0 especially is an abstraction and we somehow figured out a way to comprehend it, which is incredible to me.

Regina Barber (13:09)

Yeah. Yasmin, thank you so much for bringing us the story on zero.

Yasmin Saplakolu (13:14)

Of course. Thank you for being interested. It was super fun to report, so I'm glad others find it cool too.

Regina Barber (13:21)

If you want to hear more about how numbers can be tricky for us to comprehend, that episode is called How Big Numbers Break Our Brains. We'll link to it in our show notes. This episode was produced by Hannah Chin and edited by our showrunner, Rebecca Ramirez. Tyler Jones checked the fact that Jimmy Keeley was the audio engineer. Bette Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. Thank you for listening to Short Wave from npr.

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Regina Barber (14:46)

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