WIKIMEDIA COMMONS, JENNIFER RENSEL
What if every time you listened to Mozart or the Wu-Tang Clan your world began to change color. What if every time you touched a rough sandy surface, you felt an irrepressible jealousy. Synesthetes, or people who connect the perception of one sense with another unrelated sense or processing center, will commonly have strong associations such as these throughout their lives, often without realizing that their experiences are different.
Researchers have shown that this ability—or disorder, depending on how you look at it—may have a genetic basis. Around 50 percent of parents pass the trait onto their children, although it’s still unclear what genes are involved. With 2 to 4 percent of the population estimated to have this trait, David Brang and V.S. Ramachandran from the University of California, San Diego, wondered whether synesthesia might confer a selective advantage. The pair published their musings in an article published in PLoS Biology today (November 22), and The Scientist spoke with Brang about this unusual phenomenon—how it might be useful, and how it’s changed his own perception of the world.
The Scientist: How did you get into this area of study?
David Brang: I think the first time that I discovered it was through a friend of mine. I had just learned about synesthesia in class, I was telling a few friends about it, and all of a sudden he sort of looks over and he asks, “What do you mean you don’t see colors when you think of numbers and letters?” This was the first time I had seen a synesthete, and it tends to be the way most synesthetes “out” themselves.
TS: Why do you suspect it could be good to have synesthesia?
DB: Synesthesia is an interesting phenomenon in itself, but a secondary question is what good is it? Why would this have survived any type of evolutionary pressure? It’s possible that it was just by chance—that it co-evolved with some other process that was itself useful; it just tagged along. Another possibility is that it’s just the tail end of the distribution of how senses are perceived in the normal population. It’s not special in itself, it’s just the extremes of normal experiences.
But one thing we do find is that there are specific enhancements from synesthesia. For example, synesthesia is more common in artists, poets, novelists, and these people say that it helps their art-form. There have been a number of well documented cases over time—Kandinsky was always thought to be a synesthete, possibly also Van Gogh. One of the other interesting things is that synesthesia doesn’t just affect communication between the senses but it seems to actually enhance the sensitivity of the individual sensory systems as well. So when people see colors in numbers, they have better discrimination ability for just colors in themselves.
One of the other findings is that synesthetes report that these secondary associations aid in their memory, including anything from remembering phone numbers to license plates to remembering equations. If they need to remember “56249,” they can think in numbers, or they can think ‘well I know I saw a red color first and then there was a green and then a blue color, and so it just adds this perceptual anchor to give weight to some of these primary sensory processes.
TS: If there is a genetic basis, what might these genes be doing on the cellular level?
DB: There may be enhanced connectivity between separate brain regions. Typically the sensory systems—such as sight, hearing, taste—are usually pretty distinct. But in synesthetes we think there is actually increased communication between the senses such that there is increased white matter connectivity between each of the sensory modalities.
During development you have a huge excess of connections. Most of the regions of the brain are connected to most of the other regions and then you have this steady process of pruning through development where connections that are not efficient get pruned back so you get these efficient hubs. One possibility is that synesthesia may just be the outgrowth of what happens when pruning isn’t as successful as development may have wanted it to be, and then it has this secondary consequence.
TS: Does working on this research change how you perceive the world?
DB: I don’t have synesthesia myself, but I have definitely, over the years, developed preferences for associations. I definitely have a preference that “2” should be blue, that “b” should be yellow and that “a” should be red. I started building my own associations, but I don’t see them to any degree.
Studying synesthesia, in general, has made me more aware of the fact that our own experiences may not be universal. We can only see inside our own head.