The synesthesia gene: why did it survive?

                                                                        By: Jenna Hebert

            Most of the blog’s readers have probably heard of synesthesia, a phenomenon in which “stimuli presented through one modality will spontaneously evoke sensations in an unrelated modality.” In other words, some people can see music, taste colors, and associate numbers or letters with colors. This raises some interesting questions: where did this trait come from? Why has it been conserved in the population? While it would certainly make listening to music or reading a vivid experience, synesthesia has no evolutionary advantages...right? To address this question, V.S. Ramachandran, a renowned neurologist at UC San Diego, investigated the neural basis of the disorder. He proposed that synesthesia is the result of an excess of neural connections between different modules in the brain. Supposedly, these different regions in the brain that are interconnected in the fetus do not completely separate, leading to cross wiring. While there is no definite proof that it has a genetic basis, the trait does tend to run in families suggesting that it is transmitted from parent to offspring.

Ramachandran considers several explanations for why the synesthesia gene was concerned. Since the disorder is not deleterious or advantageous, perhaps natural selection never selected for nor against the gene. It is also possible that everyone falls somewhere along a synesthesia spectrum, and those we identify as veritable synesthetes are at the tail end. A more interesting explanation considers the possibility that synesthesia might in fact be an advantageous trait. For example, the gene is frequent among artists, musicians, and other people who spend a significant amount of time on creative activities. Ramachandran suggests that because synesthesia results from cross-wiring between different modules in the brain, it is conducive to creativity and innovation. Creativity is, after all, combining ideas or things in novel ways. Another possible advantage to synesthesia is a prodigious memory. Because synesthetes associate things with more than one sense, numbers or letters are more salient. Daniel Tammet, for example, was able to memorize pi to 22,514 digits using synesthetic associations. Ramachandran also proposes that synesthetes have an enhanced sensory processing. Depending on the type of synesthesia, they perform better than control subjects at discriminating between similar colors and demonstrate increased tactile acuity. Synesthesia and its origins clearly present a fascinating mystery to neuroscientists, and I am eager to see what future research will find.

David Brang, V. S. Ramachandran. “Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words?”