• Robb G. Best

Tasting Sounds, Hearing Colors: The World of Synesthesia

What color is Bruce Springsteen’s “Born to Run”? For many, the question may sound like word salad, but if you have synesthesia, not only might it make perfect sense, but there’s a chance you already have an answer.

The UK Synaesthesia Association describes synesthesia like so: “[s]ensations in one modality (e.g. hearing) produce sensations in another modality (e.g. colour) as well as it's own.” There are many different kinds of synesthesia. A synesthete be able to “taste” a day of the week, or describe the weight or physical texture of a word. There is little consensus about just what those cross-category attributes are: the letter M may appear brown to one person and green to another.

It’s also somewhat unclear how common the condition is; estimates range from one percent of the population to twenty percent. Part of this ambiguity stems from synesthesia being a little hard to pin down. A synesthete won’t necessarily even know that the way they process the world is unusual. Some take it for granted that sounds have smells or numbers have flavors—at least, until they confuse the heck out of their friends or family by linking the two.

What we do know: synesthesia seems to have a genetic component. If you have relatives with it, you’re more likely to have it yourself. What’s more, synesthetes tend to have above-average memories, since their double-sensing allows for a kind of built-in mnemonic device. For instance, it’s easier to imagine an address if instead of 3462, you can also envision it as red-purple-green-blue.

To the extent that it’s possible to measure, synesthetes also seem to be more creative than the general population. As such, Neurosciencenews.com reports that researchers are currently preparing to study the dreams of synesthetes. If the theory holds, their slumber will adhere to previously observed patterns among creative types: dreams will be more vivid, more emotional, and more, well, weird than those experienced by an average sleeper.

There are, however, some distinct downsides. Synesthetes are statistically more likely to have certain disorders of the immune system, including multiple sclerosis and IBS. The leading guess is that the genes which govern synesthesia are linked to some genes regarding the immune system, although the specifics remain unclear.

But which genes govern synesthesia in the first place, and how does it happen in the brain?

Holly Baxter, a synesthete herself, reports that these effects may be the result of neural connections between two otherwise unrelated brain regions. One of the most common forms of synesthesia involves linking words to colors, and interestingly, our language-processing center is right next to our color-processing center. In an fMRI machine, both regions seem to fire when this type of synesthete hears words.

Another possibility is the “disinhibited feedback” theory, in which a synesthete’s brain forms unusual connections due to the way it weights information. In this model, those novel linkages occur because the brain doesn’t prune seemingly irrelevant associations between data points.

Still, one thing’s for sure. Synesthesia brings a whole new meaning to the question, “What’s your taste in music?”

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