Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. It’s been estimated that around 4% of the world’s population has some form of synesthesia. That’s a neurological phenomenon that blurs the boundaries between the senses. Let me give you an example.

In a common form of synesthesia, when people see letters they also see colors. Or see colors when hearing musical notes. And there are many, many kinds and many combinations. But all of them involve the crossover of one form of perception to another.

This week researchers report they’ve identified several regions of the genome that may be involved in the phenomenon. Joining me now is Amanda Tilot, one of the authors of the research published this week in the proceedings of the National Academy of Sciences. She’s a Postdoctoral Researcher at the Max Planck Institute for Psycholinguistics in the Netherlands. Welcome to the program.

AMANDA TILOT: Hi, thanks for having me.

IRA FLATOW: You’re welcome. Also with us is Ed Hubbard, Professor of Educational Psychology and the Neuroscience Training Program at the University of Wisconsin in Madison. He’s at WPR Studios in Madison. Welcome to Science Friday.

ED HUBBARD: Thank you for having me.

IRA FLATOW: Amanda, this is a pretty common phenomenon. But at the same time, many people have never heard of it. I never really heard about it until we started researching this.

AMANDA TILOT: Right. A lot of people don’t realize that their perceptions are anything unusual until maybe they hear about it in a book or in a neuroscience class in college. So that’s actually a tricky thing. It’s very common, but people don’t talk about their perceptions with their friends and realize that there’s something a little different.

IRA FLATOW: So people who have it grow up thinking everybody is like them.

AMANDA TILOT: Often, yeah.

IRA FLATOW: Yeah. Ed, is this the same thing as imagining deep or musical tones? Notes as darker colors or seeing music in a minor key as dark? What is going on? Explain this for us.

ED HUBBARD: Yeah, so our thinking about this is that some of the same brain processes that are involved in, say, imagining the music as being darker, these sorts of things, might be present both in people who experience synesthesia and in all the rest of us that don’t experience synesthesia. But in people who have synesthesia, these processes are heightened or exaggerated in such a way that they do this involuntarily. They often describe it as something that happens to them as opposed to something that they do.

And they report that it’s been that way for as long as they can remember, ever since childhood. So it’s quite different at the level of how it feels to you. And that’s subjective experience. But we think at the brain level, there might be a continuum between what you and I might do voluntarily and what synesthetes report experiencing.

IRA FLATOW: You what’s interesting is when we were talking about this in the office, some people in the office– and we have a small population of people– just perked up and said, I get that. I hear that. And one of our staff people said that she gets in trouble giving people in the New York subway directions because the color the MTA has assigned, let’s say to the A train, it doesn’t match up with the color that she sees as that letter.

ED HUBBARD: Yeah. This is a quite common experience that synesthetes will report. That they have their own lifelong associations. And the rest of the world also tries to use color codes but they don’t match for any given synesthete.

IRA FLATOW: Amanda, you looked at several families of people with synesthesia. Who were they, and what did you find? What were you looking for?

AMANDA TILOT: So these were families that were originally identified about 10 years ago in a study done in the UK where they were using the best technology at the time to try and understand if there were particular parts of the genome that were associated with synesthesia that might be the same across families. So a more unifying answer that would apply to everyone with synesthesia. And they actually had a really hard time finding something like that which suggested that in individual families you might have different genetic causes.

And so that’s where the research left off. And we picked up a couple of years ago coming back to these families with newer technologies that allowed us to get really precise. So we could look for specific single letter changes in the DNA that would be associated with synesthesia in these families.

So the people in the family who have synesthesia might have these changes. And the people who did not have synesthesia would not show those changes. And we looked for those in each family separately.

IRA FLATOW: So this is genetically passed on from one member of the family to another?

AMANDA TILOT: Yes, that’s what we think. And we’ve had some indication that that was the case for about 130 years. So that idea, that it runs in families, is not new. But it’s been taking a long time to figure out exactly what was happening.

IRA FLATOW: Well, what was happening? What did you discover is happening? What do the genes do?

AMANDA TILOT: So the genes that we found that contained changes that were specific to synesthesia, those were different in each of the three families. But were expecting that based on the previous research that suggested this is going to be complex. This is not going to have one simple answer.

And so our next task was to figure out if there were any functions of those genes that would tie them all together. So maybe they’re all different, but they act in similar biological pathways. Maybe they have similar roles, maybe even in the brain.

And when we look for that, what activities were overrepresented in this big list that we had from the three families, we found that genes related to how neurons connect with each other during development, how they know where to go to send their connections to link the right circuits together, that was a function that was overrepresented in our list of genes that were showing differences in the synesthetes. And that was surprising and exciting for us.

IRA FLATOW: Ed, how does this fit into what we already know about synesthesia?

ED HUBBARD: So I think that this is a really nice bridge between the genetic level and what we were learning from more systems-level neuroscience thinking about how the brain is organized. So one of the main theories about what’s causing synesthesia is a story of crossed wires in the brain that– for example, brain areas that are involved in recognizing letters and words lie directly adjacent to brain areas that are involved in perceiving colors. And so about 15 years ago, we put forth this idea that there was some sort of what we called cross-activation.

So every time somebody who has synesthesia sees a letter or number in addition to activating those neurons in the brain that are involved in recognizing letters and numbers. They also activate some of those color cells in the brain. And that’s why they then get this automatic, involuntary additional experience of colors. And that idea has been around and it’s been supported by various different brain imaging tools.

So looking at for example, functional brain imaging, FMRI, and also looking at the structure of the brain at a very coarse level. Being able to look at how brain systems look when we look at them with MRI. But this bridge to be able to connect this up now with the molecular and cellular level and talk about these pathways at the level of these individual families I think is really exciting. And I think that this is now allowing us to build these bridges across these different levels of explanation.

IRA FLATOW: Dr. Tilot, do we have any idea what’s going on in the brain that sets these associations initially?

AMANDA TILOT: That’s a good question. So the ideas that are out there right now, and I think some of the more prominent hypotheses, are that something in your genetics, maybe differences in the types of genes that we saw, maybe differences in genes that we haven’t identified yet, predispose the brain to form these extra connections. So your brain is primed to make these extra links between your senses.

And then, exactly what links form. What color is your number six or your Wednesday is then an interplay with your environment. And that is something that has been looked at a couple of different ways, trying to see what environmental effects there are. But the idea is, so far at least, maybe that your brain is wired a little bit differently that makes it more receptive to these changes– or to these associations. And then it’s up to what you experience to form the rest.

IRA FLATOW: Let’s go to the phones to Merritt Island, Florida, to Leigh. Hi, Leigh. Welcome to Science Friday.

LEIGH: Hello. HI. Thank you for taking my call. I discovered that I have synesthesia when I was teaching a college-level composition course and I gave my students an assignment to write down what color the music was that I played. And I played some pieces of music. And not a single one of them understood at all what I was asking of them.

And when I received their blank looks I thought, oh, there’s something wrong with me. And I started doing some research and I realized this must be what it is. I see colors. I see shapes and textures when I hear music.

And sometimes it’s distracting enough that I can’t listen to it while I’m driving because it’s so vivid in my sight line. Even though it’s in my mind’s eye, it’s sometimes hard to see the road. And my son is very interested in music.

And he’s fascinated by this. And he wants to know, can you induce this in a person who doesn’t have this tendency naturally? Is this something you can learn to do when you listen to music?

IRA FLATOW: A good question. Ed, what do you think?

ED HUBBARD: Yes. This has been a question that’s been around in the experimental psychology literature and in the neuroscience literature almost as long as we’ve been studying synesthesia. So since the late 1800s really, people have asked that same question. And the answer seems to be kind of.

With lots and lots of intensive training, people can learn to have synesthesia-like associations. And a recent study has even shown that you get these really nice systematic changes in brain activity along with these changes in people’s report. But it doesn’t seem to be quite as automatic.

It doesn’t seem to be quite as stable. And the changes may go away fairly quickly after you stop the training. So there does seem to be something still different between synesthetes and non-synesthetes in that respect, but those of us that are curious about it might find a way to at least get some insight into what it’s like.

IRA FLATOW: Leigh, are you still there?

LEIGH: Yes.

IRA FLATOW: Does it help you? Do you think of yourself as more artistic because of– I’m going to call it a talent that you have with synesthesia?

LEIGH: I think that I found artistic ways to express it. For example, from the time I was very young, five years old as I first remember, I was interested in dancing. And every time I would hear music I would act out the shapes and textures that I would see with the music.

And that turned into an ability to dance. And as a consequence, since I was 18, I’ve been a professional choreographer. And I am very easily able to choreograph dances to the music because I just close my eyes and watch the music and then teach people to do what I see.

IRA FLATOW: Wow. That’s a great story. Thank you for sharing that with us, Leigh.

LEIGH: Thank you.

IRA FLATOW: Thank you for calling. I have a tweet here from Kim who says, both my husband and daughter have synesthesia. I read that it is thought we all have synesthesia as infants but that the associations diminish or disappear from most people within their first few years of life.

Have you seen any research regarding this idea? This fact, she says. Do we all have it? And do some of us keep it and some of us lose it? What do you think? Amanda, Ed?

AMANDA TILOT: Ed?

ED HUBBARD: Amanda, I’ll– go ahead. I can talk about the Dobkins Study or you can if you would like to.

AMANDA TILOT: Oh, no. Go ahead. I think that’s the one I was thinking of.

IRA FLATOW: OK, [INAUDIBLE]. You go.

ED HUBBARD: So there was a study that was done by Karen Dobkins and her team at the University of California, San Diego. And they looked at six-month-old infants and used a paradigm where they asked the infants to look at the same shape over and over and over again until the infant got bored. And then they presented things that were colored and tested whether or not that boredom from the shape also transferred to the colors.

And what they found was that individual infants would associate, for example, triangles with red. So if they had seen a bunch of triangles they were bored by red. And that suggested that the cross talk that is present for synesthetes between letters and colors might be present in infants.

And then when they looked at, I think it was nine-month-old infants, that cross talk seemed to go away. And so this does suggest that early in development there is some of the same cross talk that’s important for synesthetes having their lifelong associations between letters and colors.

IRA FLATOW: This is Science Friday from PRI, Public Radio International. Now, Amanda, I understand you are studying synesthesia and you need volunteers. Right?

AMANDA TILOT: Yes, we do.

IRA FLATOW: You have a big megaphone right here. How can people sign up?

AMANDA TILOT: If you experience connections between letters and numbers or days of the week and colors, we would love for you to join our study. You can start by going to our website. It’s www.mpi.nl/synesthesia. And if you click on Join This Study, you can learn a little bit more about synesthesia, take some short quizzes if you’re not sure.

And if your types that you experience are the right ones for our test, we’ll send you a genetic test in the mail. And you can mail it back to us. You can participate from anywhere in the world. And we pay for the shipping.

IRA FLATOW: There you go. Their website is mpi.nl/synesthesia. We’ll try to get it up on our website later on. In a minute we have to go. Ed, you’re studying educational psychology. Now, does this affect the classroom? synesthesia?

ED HUBBARD: This is part of what we’re looking at now. Synesthetes will say that sometimes their colors help them to remember things like phone numbers or math facts. They will also say that sometimes they get in the way when, for example, the colors for three and four don’t mix to create the color that seven should be. Or two plus five, which are different colors, are supposed to give them the same color for the seven.

So synesthetes say it helps them and it hurts them in all sorts of interesting ways. And we’re still trying to understand this. And so we’re looking at adults, college students here, that have synesthesia, and also looking at children trying to understand better how these synesthetic associations help and hurt their learning.

IRA FLATOW: Well, good luck to both of you. Ed Hubbard, Professor of Educational Psychology and Neuroscience Training Program, University of Wisconsin and Madison. And Amanda Tilot, Post-doctoral Researcher, Max Planck Institute for Psycholinguistics in the Netherlands. Thank you, both, for taking time to be with us today.

ED HUBBARD: Thank you, Ira.

AMANDA TILOT: Thanks for having us.

IRA FLATOW: You’re welcome.

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