The colors that letters and numbers appear to a synesthete
What’s the News: For most of us, our senses stay relatively separate: that is, we hear what we hear and see what we see. People with synesthesia, however, actually see words as colors, taste a particular flavor when they hear a familiar song, or experience other strong, automatic linkages between senses. The neurological underpinnings of the condition—how the brain connects two usually distinct senses—have remained a mystery. But researchers have now found a possible cause, they reported yesterday: neurons in the area responsible for the second sensation, such as the color that goes with the word, may be unusually excitable.
When researcher Julian Asher goes to the symphony, he gets a sensory extravaganza. “When I hear a violin, I see something like a rich red wine,” says Asher…. “A cello is more like honey” [New Scientist]. Asher has a condition called synesthesia in which sensory information gets mixed in the brain; in Asher’s particular form, auditory-visual synesthesia, sounds cause him to see colors. Now, a study led by Asher may have uncovered the genetic source of the condition, which synesthetes say can be both a blessing and a curse.
The researchers collected DNA samples from 196 people who had auditory-visual synesthesia running in their families, they explain in the American Journal of Human Genetics [subscription required]. Asher expected to find a single gene associated with the condition, but scanning the genomes revealed that it was linked to four distinct regions, on chromosomes 2, 5, 6, and 12.
The region that was most strongly linked to synesthesia was an area on chromosome 2 that has also been strongly linked to autism. That doesn’t mean that the two conditions are related, per se, explained Ed Hubbard, a cognitive neuroscientist…. Instead, the common gene or genes are likely “more generally involved in how the brain gets built.” The study also pulled out a region on chromosome 6 that contains genes linked to dyslexia — especially interesting, “seeing as phonemes [the units of sound in language] and letters are two of the strongest synesthetic triggers,” Asher said [The Scientist].