Do you see blue the same way I do on the inside? Why do some people think the northern lights make noise? Why do you think the low note on the piano is larger, and the high note brighter? Join Eagleman on a wild ride into the world of synesthesia, a topic his neuroscience laboratory has pioneered for years.
Why do some people think that the Northern lights make noise and other people say that that's impossible. And why did Pythagoras think that numbers had colors and personality? And what does any of that have to do with creators like Vladimir Nabokoff and Billie Eilish, And why do you think that a high note on the piano is brighter than a low note. Welcome to Inner Cosmos with me, David Eagleman. I'm a neuroscientist and an author at Stanford University, and I've spent my whole career studying the intersection between how the brain works and how we experience life. On today's episode, we're going to talk about how we can all experience reality a little bit differently. Okay, so this story begins in the early nineteen thirties. You've heard about the Northern lights, or maybe you've even seen them in person. They're these rippling rivers of green blue light in the sky. But here's the really strange part. About one hundred years ago some people started to make the claim that the northern lights make noise. In nineteen thirty one, in the journal Nature, a scientist named Harold's Fairdrop wrote a short paper that he called Audibility of the Aurora polaris, and he wrote, quote, it cannot be doubted that many persons have heard a distinct sound when watching a brilliant display of aurora. Communications regarding the auroral sound appear now and then, and recently.
Mister J. H.
Johnson has collected a great number of reports on the auroral sound in his pamphlet concern the Aurora borealis. Then, in nineteen thirty three in the journal Science, someone named Clark Garber wrote another letter on the audibility of the Aurora borealis, and Garber wrote quote, some scientists have claimed with much positiveness that the aurora emits no audible sounds. In my own mind, there can be no doubt left as to the audibility of certain types of aurora, for I have heard them under conditions when no other sound could have been interpreted as such, for no other sounds were present. And he goes on to say that he first heard about the possibility that the aurora makes sounds from the eskimos, and he says he was skeptical at first, but then he experienced this sound himself. Now I stumbled on these papers a few years ago, and I was surprised because the problem is that it's not scientifically possible for the Aurora to make sound. The Northern Lights happen because photons from the Sun are banging into gases in the Earth's upper atmosphere, and that causes all that amazing light. But those collisions are happening eighty kilometers up in the sky, which means that even if there were sound, it would take about four minutes for that sound to get down here. And yet people who claim to hear the sound say they see it happening in lockstep with the lights. And more importantly, for sound to travel it needs a medium like air, and that's because sound moves as compression of the air. In other words, molecules in the air get pushed closer together and farther apart, and that's what a sound wave is. But at the altitude where the Northern Lights come into being, the atmosphere is essentially a vacuum.
So this means there's probably no.
Sound happening even up there, and if there were, it couldn't get all.
The way to us until four minutes later.
So this became a top of debate because as time went on, thousands of Arctic explorers listened carefully for these sounds but didn't hear anything. So this idea of the northern lights making noise came to be understood as a superstition. So what was happening here? Were some people simply lying in scientific journals It's happened before, But it seems that some people really believed and still believe, the lights make sound, even though the physics don't seem to allow that. So worse Ferdrup and Garber lying, were they looking for attention that they somehow have better hearing? Even today? This is contentious in geophysics. Some people argue from their personal experience that it happens, and others point out that it simply can't. To unpack this mystery, let's jump back even farther back another twenty five hundred years to Pythagoras. Pythagoras was one of Greece's most famous philosophers, and he massively influenced the trajectory of Western thought through his religious teachings his political teachings. In part this was due to his influence on Plato and Aristotle. But you've probably heard of Pythagoras because of his love of numbers. He loved geometry and theories about instrument tuning and the theory of proportions, and you'll probably remember the Pythagorean theorem from school in a right triangle, A squared plus B squared equals C squared. But there was something very odd about Pythagoras's relationship with numbers. I'm going to quote from the Yale historian Robert Brumbaugh, who notes that for Pythagoras quote, each number had its own personality, masculine or feminine, perfect or incomplete, beautiful or ugly. For Pythagoras, ten was the very best number. This feeling modern mathematics has deliberately eliminated, but we still find overtones of it in fiction and poetry. Now, how could numbers have gender and personality? Did Pythagoras have fundamental insight about numbers that the rest of us couldn't see? Or was he making up stuff to impress his followers, or was he mentally ill or taking drugs. The way that he personified numbers is traditionally discussed as an interesting oddity, or occasionally you'll find numerologists who cite Pythagoras's view as evidence that he had a cosmic insight into the true natures of numbers. I've seen websites that springboard from Pythagoras's number personalities to sell new age models of the nature of the universe. But most people don't believe that the number five has a gender or a personality. So what was going on here and what does this have to do with the scientists who claim to hear sounds from the Northern Lights. The answer to both these mysteries is related to something I'm going to discuss a lot across many episodes of this podcast, and that is the difference in people's internal worlds. We all like to believe that our experience of the world is the same as everyone else's. But the key to unlocking the mystery of the Northern Lights or Pythagoras's view of numbers is to understand that people can have very different realities on the inside. The interesting part, as we'll see, is that we accept the reality presented to us. Your brain constructs a story about what's going on out there, and you accept that as your reality. So imagine I showed you a picture of a crowd of people. If you're color blind, all you see are shades of gray. If you're not colorblind, you see it in full color. But either way, that's the reality that you know. And we now know that a very tiny fraction of the female population doesn't just have three types of color photoreceptors in their eyes, but they have four types because of a mutation, and as a result, they perceive colors that the rest of us can't even imagine. Their reality is different. So the key is we accept whatever reality our brains serve up to us. Okay, So this all leads to a very old philosophical question which I think everyone has asked at some point in their lives. How do you know that what I see as blue is what you see as blue? My parents taught me to call that thing blue, and your parents taught you to call it blue.
Two. But inside your.
Head and inside my head, it might be a different experience.
Right.
I might be seeing it as what you would think of as green, But it doesn't matter, and we'd never know as long as we can transact in the outside world. In other words, if I say, hey, can you pass me that blue thing, and we both call it blue, then the word suffices, even if we're having a different internal experience and it turns out. The situation might be even worse than that. It may be that what I call vision and what you call vision are totally different. I might see the world completely upside down from the way that you see the world, and it wouldn't matter as long as we can agree on things out there, and I can throw a ball and you can catch it. So what my colleagues and I have worked on for years is taking this question or we having different lives on the inside and elevating that from the realm of phys sophical speculation to actual scientific experiment. And one way to get at that this was something my lab is studied for fifteen years called sinnesthesia. Synesthesia is a condition in which one person might be seeing reality a little bit differently from another. So you know the word anesthesia, that means no feeling. Synesthesia means joined feeling. It's a blending of the senses. Now, there are many forms of synesthesia, and one of the most common is where a person looks at numbers or letters and that triggers an internal experience of color. So for a given synesthete, her eight might trigger the experience of blue. She still sees the number eight on the page. There if I were to write eight with black ink on a white page, she'd say that she can see the number, but seeing the number eight triggers a blue experience, an internal experience of blue. And it's just self evidently true for her that eight and blue are connected. Now this isn't just a memorized thing that she says, but it's an actual experience. And for her, maybe five is yellow, and Saturday is orange, and November is purple and so on. Now, the first thing to note is that sequences that we learn, like letters and numbers and weekdays and months, these are drilled into the brain really deeply. They're known in the field as overlearned sequences, and these are the things that trigger synesthesia. And interestingly, this often goes beyond color in when flavor of synesthesia, sequences come to have gender and personality and other qualities. So one cynesthete describes the number three as a vain, elitist girl, while seven is a shy, wimpy boy. This same cynisthe described by my colleague Sean Day. She also noted that she doesn't like certain number combinations, like ninety four.
That quote result.
In putting four, which is a plain but decent, hardworking older woman and nine together as they greatly dislike each other and do not get along well. And this is what was going on with Pythagoras. He had this not uncommon form of synesthesia, but his followers didn't know this, so they presumably thought he was tapped into some cosmic truth about numbers. He obviously liked numbers, but that doesn't mean he had access to some deeper significance that others didn't. How do we know that, Because each person with this particular type of synesthesia has a different association between a particular number and a gender personality. So you might think three is male and kind, and someone else might think three is female and a bit of a comic, and so on. There is no right answer. So we're gonna come back to this in a moment, But first I want to tell you about some other forms of synesthesia. It's not just colors or genders or personalities triggered by overlearned sequences. There's also a flavor of synesthesia in which what you hear causes a visual experience. So you might listen to music and that causes you to see moving shapes or colors. In my book, Wednesday's Indigo Blue. I have a picture of a shape that looks like a colorful caterpillar, and this is what one synesthete sees. She actually sees this when her furnace kicks on and goes whoosh. She has this visual experience that flashes for her. Her visual system gets tickled by the noise, and senses can be triggered in the other direction, where something visual leads to a sound. For some people, when they watch movement like a swarm of moving birds or an electric sign blinking, they feel like they hear a sound with it. They don't see the motion by itself. Their brain imposes sound on top of that. It's impossible to separate the motion and the sound. And I've proposed that this is the solution to the mystery of the Northern lights. It's impossible from a physics point of view for the lights to be making synchronized noise. But what is possible is for a small fraction of the population to be cinnesthetic, such that when they see the beautiful moving lights, they hear sound. And because of their assumption that our senses tell us the truth and that everyone should be having the same experience, this has led to over a century of debate about whether the lights make noise or not, because if your sphare drop or Gerber or any of the others who hear the sounds, you'll sit down and you'll write a letter to nature or science and insist that you can hear it. The important lesson is that we all assume our senses tell us the truth and that everyone is tapped into the same reality. But when we realize that's not necessarily the case, we can take a higher view on the scientific literature and look at all these papers going back and forth about whether the northern lights make noise, and we can understand the game at a different level. For most people the answer is no, they don't make noise, and for some it's yes. Beyond the relationship of sound and vision, there are dozens of forms of synesthesia. My colleagues and I have found that essentially any sense that you can imagine can be mixed with another. One form of synesthesia involves tastes shapes, So when people taste something, it makes them feel like they're touching something with their fingertips. So you might take a sip of soup and you feel something cold and pointy on your fingertips. Or one guy determines whether his chicken is cooked right this way. He tastes it and judges by what he's feeling on his fingertips, is it smooth or glassy or spiky. He comes to be a good cook that way. And there's also musical synesthesia. For a lot of people, different notes of the scale will trigger a color experience. For one cynisthee that I test in the lab, when she hits the note A on the piano, that's pink, the note B is blue. C is goldish white like sunlight. B is silvery white like moonlight. E is fiery orange, and so on, So she experiences very specific colors that get triggered when she hears specific notes. And I know a professional drum tuner who goes around for all the famous rock and roll bands and tunes their drums, and he does it with color, so he can tell if the drum is a little bit sharp or a little bit flat by the color that he sees in response to the sound. Now, not all people with music synesthesia have their percepts triggered by a pitch a note. For some people, it's the interval between notes like a chord that matters. So for one woman, different chords trigger different, very particular tastes in the mouth. In a paper in the journal Nature, she reported that she uses these sinnesthetic associations to identify which chord was just played. And synesthesia can also be triggered by an instrument's tamber, the way that it sounds. So when a person hears the music of a violin versus a tuba, versus a cello versus a flute, the timbre of the instrument can trigger very different experiences in terms of colors or visualized shapes or whatever. So two people might listen to a clarinet playing and that triggers different internal experiences. One of them sees it as a flat, horizontal shape with spring like protrusions sticking out, and the other person sees it as a thick ribbon that's oscillating, and so on. For different cinisthetes. And beyond shapes or colors, it can trigger other notions as well, like personalities. One cinis The reports that the obo is quote profoundly emotional and thoughtful, with drawn, introspective, and prone to melancholy, while she describes the flute as quote feminine, sweet, innocent, naive the personalities of the different instruments. They're not generic, they're rich and detailed. The triggered perception can also be a physical sensation, like a physical state of your body. For one Cyniceitt that I interviewed, different chords make her feel like her body is in different positions physically, So when she feels one chord, she feels like she's standing upright with her feet on the ground, or stepping onto a stare or soaring in the sky. She happens to be a professional musician, so when she's memorizing a piece of music, it's like memorizing a series of dance moves. And there's one more form, which is likely the most common, around ten percent of the population experience it. It's when people perceive sequences like the days of the week or the months of the year, as though they have a specific space location in relation to their body, like March is off here to the left, and April is next to it, and May is a little bit higher and off next to that. For every month or a weekday or numbered things like that, they have a specific spatial location that the person can identify where it seems to them that the thing exists. It's just self evidently true to them that that member of the sequence has that particular spatial location. This form of synesthesia is not a hallucination. It's not that you actually see April right there visually.
It's that it's just obviously true to you.
That April would occupy that spatial location to you. It would be like if I asked you to imagine an apple five feet in front of you. So you're picturing the apple there and it's got a particular spatial location with respect to your body, and you can imagine it, but you're not actually hallucinating it. But if I ask you where that apple is, that's the spatial location that it has. A lot of people have this form of synesthesia for years, like the year nineteen seventy nine has a specific spot in space and relation to your body, as does twenty twenty one or twenty fifty seven and everything in between, and the years sit on this spatial timeline. The timeline isn't necessarily straight. It can curve or take sharp turns, and it typically moves with the passing of each year. Now, what's interesting is that for many cinisthetes, a year in the past moves behind them, say the year twenty twenty one. Why because that year has already happened, so it moves behind you, while a year like twenty forty two is often the distance ahead of you. But for other cynisthetes, it's exactly flipped. A year in the past is in front of them because they already know what happened in twenty twenty one, but year like twenty forty two hasn't happened yet, so they don't know anything about it. It's as invisible to them as an object that is behind them. I'll just note that another research group called this form of synesthesia time space synesthesia because they looked at things like weekdays and months and years and said, hey, those all have something to do with time. But I want to emphasize that this is not the correct way to understand this, because this same spatialization happens with number lines like one, two, three is over here, that it takes a right turn here for four through seven, then eight, nine, ten climb straight up, then eleven through twenty shoot off in a straight line, and then twenty one through thirty are stacked above that like that.
Kind of thing.
And also we find cinisthetes who have spatialization for the Indian caste system, or shoe sizes, or temperatures, or historical eras or primetime television line. So it can be anything that's a sequence, and it just so happens that time is sequential, but it's just a subset of the sequences that you might learn in life. And that's why I named this spatial sequence synesthesia in the literature, which is the name now used in the field. It turns out there are many, many forms of synesthesia, and one group has estimated that there are one hundred and fifty two different forms that have been reported. So anything you can imagine, any kind of cross blending between the senses has been reported at one point or another.
Beyond the spatial sequence synesthesia.
The next most common one seems to be the letters or numbers mapping on to colors, or weekdays and months to colors, or musical sounds to colors, or smells to colors, or taste to colors. Most forms of synesthesia trigger color, but we also find triggered tastes, smells, sounds, temperatures, emotions, and so on. We find essentially any kind of cross sensory blending that you can think of. It appears that synesthesia is different for every synesthet Her associations are different from hers, are different from hers. So the color that gets triggered by the letter J or the number three is a different color for everyone. Now why is this. It could be that it's just about random wiring in the brain, so the particular letter that matches up to a particular color is arbitrary. But my colleagues and I started to wonder if instead of randomness, it could be about something that you imprinted on as a young child. Now, this would give essentially the same results as randomness, because you might, as a child see an alphabet quilt that your mother made, and your mother's choices were just her random choice, or an alphabet poster that your teacher made at your preschool with some random choice, or some ad in a magazine, and the idea is that those particular letter color associations stuck for you. For most brains, the statistics wash out, which means that one day you see an A that's red, and the next day you might see an A that's blue, and the next day yellow, and so on, and so your brain learns that A is not associated with any particular color, but in a synesthetes brain, for whatever reason, perhaps the first association that they see sticks and doesn't get washed out. Now, how could you possibly test for this imprinting given that there's no easy way to know what people saw in their childhoods? And this is where science comes in. I collected detailed colored alphabets from almost seven thousand cynisthetes who had these colored alphabets, and with two colleagues at Stanford, we analyzed those colors in detail, like person number one has a red A and a purple B and a yellow C and so on, and the next person has a brown A and a crimson B and a gold C and so on. So we analyzed this huge pool of cynisthetes and we found something amazing. At least six percent of the cynisthes had approximately the same colors. A through F went red, orange, yellow, green, blue, purple, and then this same sequence of colors was repeated G through L, and then M through R and so on till the end of the alphabet. This was so weird, and even more of a clue is that we looked at people's birth year and this sequence of colors never came up for people who were born before the late nineteen sixties, and then the proportion of people started to rise. So for cyniesites born between nineteen seventy and nineteen eighty five, fifteen percent of them had this same sequence of colors for their letters, and then for those born after nineteen ninety the proportion decreased again. So what was going on here? We figured it out. In nineteen seventy one, a new toy started finding its way into homes all over the United States. It was the Fisher Price magnet set. This was a set of refrigerator magnets that consisted of the letters of the alphabet, and each one was colored and it cycled through the letters red, orange, yellow, green.
Blue, purple.
So for those born in the decade after the magnets existed, this color pattern reached fifteen percent. But for those who grew up before the magnets existed, not a single one of them had this pattern. So for all of these cyinsetes, it was about whether they were exposed to these magnets as children. Now, I want to be really clear that the synesthesia wasn't caused by the Fisher price alphabet set because the rest of the population saw it in the seventies and eighties, but only three percent of people become cynisthetes. It's simply that the sinisthetes who saw it imprinted on it, so that.
To them A always.
Triggers red, and B orange, and C yellow and so on. Synesthesia is something we think of as a different way of perceiving the world. It's not a disorder or a disease, because there's no disadvantage to it. In fact, in some cases, cinisthetes tend to have better memories. So if I were to tell you my phone number and you are a sinisthete, you might forget some of the digits, but you may think, oh, yeah, I remember it had a really nice autumn color pattern to it, and so that would help you to reconstruct.
It later when you're trying to think of it.
You may have heard the termmneminists spelled with an m N like Johnny mnemonic or a mnemonic device. Anyway, aneminist is a person with an incredible memory. They can memorize long lists of nonsense words, or really long strings of numbers or series of locations. It turns out as far as I can tell, that every single one of these mneminists have synesthesia. They can take something like the digits of Pie three point one four one five, nine, two sixty five three five, and for thenemenist this may have colors, such as the colors helped them to memorize the sequence. And more than colors, they may have also textures and personalities and genders and sizes, So as they're learning three point one four one five, nine two sixty five, there's a whole story landscape with a rich texture. So this is how they memorize Pie to thousands of digits, while for the rest of us who aren't synesthetic, for whom all numbers are essentially alike, it's an almost impossible challenge. I'll just mention that this advantage of synesthesia can also become a confusion in some circumstances. So one synesthete has particular colors that he sees for names like Mike and Dan, but it turns out that he sometimes runs into trouble at cocktail parties because it just so happens that Dave and Rob have exactly the same colors for him as Mike and Dan. So if your name is Dan, He's pretty likely to mess up and call you Rob later in the night. It turns out many artists have synesthesia. Vasili Kandinsky was a music to color cinesthete. So if you can picture a Kandinsky painting, you know that he has these bold brushstrokes and vibrant colors. He makes these abstracts with a sense of movement and energy. Boy, you might not know is how he made them. He would crank up his phonograph and he would stand in front of his canvas and paint the images that came to his head from the music that he was hearing. So what you see on the canvas are his renditions of his synesthetic experience. And many writers are cynisthetes. Vladimir Nabokov, who wrote Lolita, was very synesthetic with letters and numbers. These would trigger colors for him, and as a young man he actually wrote quite a bit of poetry about how he saw letters. When he was asked what color his own initials were, the Bokhoff answered quote, the D is a kind of pale, transparent pink. I think it's called technically quartz pink. This is one of the closest colors that I can connect with the V, and the N, on the other hand, is a grayish yellowish oatmeal color. Interestingly, different colors were triggered for him by the same letter in different languages, so he said, quote the long A of the English alphabet has for me the tint of weathered wood, but a French A evokes polished ebony. This black group also includes hard G, vulcanized rubber and R, a sooty rag being ripped, oatmeal, N noodle, limp L, and the ivory backed hand mirror of an O. Take care of the whites. I am puzzled by my French on, which I see as the brimming tension surface of alcohol in a small glass. As a side note, Thebokoff loved butterflies, and one of his favorites had yellow wings in a black middle. So when yellow black yellow, and that corresponded for him to the letters ab a so boom. That became the title for his great novel Aida. It was his little insider synesthetic joke, and many musicians are synesthetic. Take Amy Beach, who was the first successful American female composer. Her biographer noted that for her, C was white and F sharp was black. And e was yellow and so on. Until the end of her life she associated those colors with those notes. Or The composer Olivier Mession, he was synesthetic, and he described his purpose as quote, painting the visible world in sound. He would describe things in his diary like, quote, the gentle cascade of blue orange chords. This is the way that he would describe particular sequences of music. There are lots of musicians with synesthesia. Billy Joel, Duke, Ellington, Torry, Amos Grimes. The singer Billy Eilish recently told Rolling Stone quote, every person that I know has their own color and shape and number in my head, but it's normal to me. She says that her brother Phineas is an orange triangle, although his name Phineas is dark green. Pharrell Williams also has synesthesia. For him, each note has a color, and his musical group Nerd named one of their albums Seeing Sounds. Now people have speculated, because of this sort of thing, that maybe there's an overrepresentation of sinnisthetes in the artistic community. But I just want to point out that we don't actually know if that's true, because no one's ever gone in and tested the community of accountants or deep sea divers. All we know is that we can point to a lot of artists who are synesthetic, and so we can hypothesize that maybe synesthesia provides some pull to those professions. In other words, if you have this slightly richer sort of perception, then maybe you gravitate towards certain sorts of pursuits. By the way, I should note that not every artist who does something synesthetic is actually a synisthet The composer Scriabin was really interested in the effects of putting sound and color together, and he thought that would provide a really strong resonance for the listener. So he invented a color organ. When you hit the notes, you're not only playing the musical sound, but there are spotlights of different colors coming out of the top. But Screopin wasn't actually a synisthete himself he was just exploring cool things and was influenced by the fashions of the art world at that moment. So not everyone who does this sort of thing is actually a synesthee. And this leads me to a really important point. How can you tell if someone really is synesthetic? How can you test for this. So when someone tells you that they're a synisthete, how could you ever know if they're just being artistic or metaphorical or poetic, or lying or just trying to get attention. So my colleagues and I, over the past fifteen years, have developed a whole series of tests where we can show when synesthesia is actually a real perceptual experience. And I want to tell you how we do that. It has everything to do with the consistency of people's perceptions. So if you're a cynisthete who sees eight as lavender, you're always going to see it as lavender. But if I were to ask you to make up some colors right now, and then I ask you again a year from now, if you're not synesthetic, you're not going to be able to get these same color associations. But if you are synesthetic, it'll be the same colors. So many years ago I launched a website called cinnisthete dot org, and it's a battery of tests that are freely available. So if you think you might be a synthete, go to the site and take the tests. What we can do this way is rigorously determine who exactly is synesthetic and who's not. Here's the method. It has anything to do with internal consistency. So we show you a letter of the alphabet at random, say a J, and you see a color palette on the screen, and by moving a slider around, you can get to any hue, any color, and by moving a second slider around, you can specify whatever saturation, in other words, how dark or bright it is. So you pull the sliders around and you pick the color that best matches your synesthetic perception for that letter. And this is out of sixteen million different colors that can be displayed on a computer screen. And when you found the best one, you click submit, and then you get the next random letter or number, say the letter W or the number three or whatever, and you find exactly that color that best matches for that one. And the trick is we present you with each letter and each number three times, each in random order. So the idea is that if you are really a synesthee, you're going to land on the same shade of color for let's say the letter J every time. And if you're a sinisthete, it turns out it's very hard to fake that. So when you look at the results for cynisthetes and for control subjects who are asked to fake synesthesia, we can measure the amount of difference in the colors that they chose. And what we see is that for a real cinisthete, it's easy. Every time she's presented with the letter T, she picks the same color or E, it's the same color every time, and so on. Whereas for somebody who's asked to use free association or memory or whatever but they're not actually synesthetic, it's really difficult to get the same colors. It's a very hard test to pass to remember what you said fifty seven trials ago and find that color again out of sixteen million possible colors. So this turns out to be a powerful way that we can distinguish who is a cynisthete and who is not. And we actually have several levels of testing to make it absolutely impossible to cheat. So, for example, after we've collected your colors, we then flash it to you on the screen. So let's say it's the letter H. We flash an H that's either the color that you've had chosen or a different color from somewhere else in your palette, and you have to say as quickly as you can whether it matches or didn't match your perception. And for a real cynisthete, if I'm flashing the orange h they'll say, yeah, that match, and if I flash a green age, they'll say that doesn't match. But for someone who's just faked their way through, it's something they're terrible at, both in terms of accuracy and reaction time. So this is how we can make sure that we find real cynisthetes. And we've translated this battery into many different languages, including Chinese and Hebrew as well as a whole bunch of European languages, and this way we can find out what's going on not only in French and Spanish and German, but also in different alphabetic systems like Cyrillic or Hebrew or Chinese. Also we can test all sorts of different forms of synesthesia. And what we have now are about eighteen different forms of tests, like musical notes to color, or instrument tambers to color and so on. And it turns out with this sort of testing we can finally get the sample sizes that we need, because it turns out that all the previous literature had a sample size of one. Up until the early two thousands, it was all single case studies where people said, hey, I met a cinisthet and I asked her these questions and here are her answers. And then people started publishing papers with a participant group size of two or four, and a few papers had eight people in them. What we've done now is changed the game on that because we have rigorously verified over sixty four thousand cinisthetes and we have their data in exquisite detail, and this allows us to alter the scientific playing field. Now, there were a few papers on synesthesia in the eighteen hundreds, but then synesthesia essentially slipped out of the scientific spotlight for most of the twentieth century, and that was because psychology was dominated by the behaviorist school of thought, where the idea was that we're just input output reflex machines and it wasn't really appropriate or scientific to talk about private subjective experience. So as a result, synesthesia fell to the wayside. But fundamentally, if there's one thing we know, it's that it feels like something to have a brain. We have private subjective experience consciousness, and so as this question has become a serious one in our field. Synesthesia has risen from the ashes as a powerful inroad to understanding consciousness. So what causes synesthesia? My colleagues and I have performed brain imaging and what we found is that in a cynisthete, neighboring areas of the brain have a little bit more cross.
Talk than normal.
So regions of the brain that care about letters and numbers happen to be close to other regions that care about colors, and in a sinisthete, there's a bit more cross talk between these areas than in a typical brain. So think of it like two neighboring countries with porous borders. And some years ago my lab started a long term project to find the gene or genes that underlie synesthesia. And to my mind, this is the first step in a new subfield, which I'm calling perceptual genomics, which just means understanding the subtle genetic differences that make you see the world differently than I do. As a scientific community, we're always looking for the genes for predisposition to diabetes or aortic stenosis or Parkinson's, or that make some people taller or broader or red haired or whatever. The same techniques can be used to find the genes that make our realities a little different from one another. Something that struck me, as I mentioned earlier, is that there are many different subtypes of synesthesia. Now are these all the same thing or different? In other words, are all synesthesias due to a single genetic change or are there totally separate mechanisms involved? So how could I answer this? We tested all these thousands of people on synesthesia, and we asked from the data how the different types cluster with one another. In other words, if you have colored letters, what is the likelihood that you also have instrument tamber synesthesia or colored months or colored musical notes or something like that. How do these different things clump with each other. What we found is that if you have colored letters in number, you're really likely to have colored weekdays or months, but you're not terribly likely to have other forms of synesthesia like vision to sound or taste to touch. And what we found is that the different types fall into five different clusters.
If you have touch to color.
You're not really likely to have sound to touch or other types. They fall into these different groups. And if you want to know more about this, go to Eagleman dot com slash podcast to see our different papers on this. Now, this is an important finding that I'm mentioning because it suggests that synesthesia is not a single thing genetically, but there may be at least five different things that we're all putting under the same umbrella. And the reason we put them under the same umbrella is simply because they have something in common. There's a mixture of the senses, but they might actually be underpinned by different genetic bases. And this is something I'll talk about in future episodes, because we're generally seeing the same thing when we look at other things like schizophrenia. People can present clinically very differently, but we lump it all under schizophrenia. But I think it's likely that in ten years from now, we'll talk about multiple types of schizophrenia, and eventually we'll have totally new names that identify the different genetic causes that happen to give rise to these similar conditions that we stick under the same umbrella. So the one that I've been concentrating on is the one I call colored sequence synesthesia, because as I mentioned, the thing to note is that letters and numbers and weekdays and months are all overlearned sequences. They're all arbitrary sequences that you memorize when you're about four or five years old. And the way I started this genetic study was by crashing a wedding and asking everyone to spit into spitkits. Now why a wedding, It's because the whole family tree of this family with synesthesia was there, so I could march through the tree to see who has synesthesia and who doesn't, and then do what's called a family linkage analysis, which looks at how the small genetic changes march through the family tree and you find out which tiny changes are tracking with who has synesthesia. Now, we're still working on this with lots of different families in their trees, and it may well be that there are different genetic changes in different families, but we're getting closer to identifying at least some of the genes involved. Now, this might involve an increased wiring in a cineste's brain, or it might involve a slight imbalance of the inhibition and excitation in the brain such that you have activity in one area that kindles activity in the neighboring area. I actually favor the second hypoth this because non synesthetes can experience synesthesia with drugs, and people can also experience synesthesia sometimes if they're super tired and someone slams the door, they'll see colors. Even for synesthetes, there synesthesia waxes and wanes a bit. Whether they're stressed or fatigued, or on cigarettes or alcohol, or antidepressants or anti epileptics. All these things change the quality of their synesthesia. And that has the feeling of something to do with the chemical balance, not simply the hardwiring. So I think that when we find the gene or genes, will be able to show that it's something associated with the balance between inhibition and excitation in the brain. So what's amazing about synesthesia is that what might be a single nucleotide change in your genome changes the way that you see the world. It changes the way that you experience and it's your reality. So this will be the first time that we're able to say, if you change this little A or C or T or G over here, now you are seeing the world differently. Now I want to ask you a question. I'm going to play two notes on my piano, which one is brighter, which one is bigger. I've asked this informally to thousands of nonsynesthes and essentially everybody answers that the high note is brighter and the low note is larger. And that's strange, right, because all I'm doing is playing some notes, and you're mapping that sound onto brightness and onto size. So what this suggests is that everyone has some cross connectivity in the brain. And when you look at the micro anatomy, what you find is that there are fibers in the brain carrying visual information that go into the auditory part of your brain, and there's fibers carrying auditory information that plug straight into the visual parts of your brain. So this isn't everybody's brain. It turns out there's naturally a lot of mixing of the senses, and that's presumably why we all understand expressions in the language that cross the senses, like oh, that's a loud tie, or that's cool jazz, or she has a sweet personality, or that's sharp cheese. Cross sensory expressions are all over the language, and they kind of work with everybody.
We all know what it means when.
You talk about these So this is the sense in which we all share something like synesthesia, but we only call it synesthesia when it's a cross sensory connection. That's rare, And in this way synesthesia can serve as a terrific inroad into understanding consciousness, both what people have in common and what they experience differently. It illustrates a theme that I'm going to come back to a lot in this podcast, which is that people can be quite different on the inside. So, to wrap up today's episode, reality is not one size fits all. Two people can stand right next to each other watching the Northern lights, and for one a sound is internally triggered by the visuals, and not for the other. Two humans watching the same event and having divergent experiences. And the important lesson here is that if we're just trying to understand our own reality, we're like fish in water trying to describe water. It's impossible to describe what water is because we've never seen anything other than that. But when you see a different way that things can be, that gives you a broader platform from which to build theories, and that allows us to make progress on one of our deepest goals in neuroscience to understand how the microscopic activity in these three pounds of wet, gushy alien computational material maps onto the world that you see and enjoy every day, How it maps onto the view that you're looking at right now, or the feel of your clothes on your skin, or the sound of my voice in your ear. That's all for this week. To find out more and to share your thoughts, head over to eagleman dot com slash podcasts. If you think you might have synesthesia and you want to take the tests, go to sinnisthet dot org. Until next time, I'm David Eagleman, and this is Inner Cosmos.