The condition known as synesthesia is one of the most mysterious phenomena in all of neuroscience. The term refers to a perceptual glitch in which different senses seem to be crossed up in the brain — people might “see” certain sounds or “hear” particular colors.
Scientists have observed that synesthesia seems to run in families, and new research published this week confirms that there is almost certainly a genetic component to the condition.
In a report published in the journal Proceedings of the National Academy of Sciences, researchers from the University of Cambridge and the Max Planck Institute for Psycholinguistics reveal new findings that help explain the biological origins of synesthesia. The new research contributes to a growing body of data on the condition and could also help scientists better understand how the brain processes sensory input in general.
“We knew that our genetics can influence other aspects of perception, like the intensity of pain or bitter flavors, but connections between senses like in synesthesia have been harder to study,” Amanda Tilot, lead author of the research and a geneticist at the Max Planck Institute, said.
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Previous brain imaging studies have demonstrated that people with synesthesia process sensory input differently than those without the condition. But scientists don't really know how the perceptual differences develop in the first place.
“We hope our results will help us get closer to bridging the gap between knowing that synesthesia is at least partially genetic and knowing how the brains of adult synesthetes are wired a little differently compared to non-synesthetes.” Tilot told Seeker.
The research team took advantage of recent advantages in genome sequencing to track three different families in which multiple generations have experienced color when listening to sounds.
“Each of the synaesthetes in the families had sound-color synesthesia,” Tilot said. “Their experiences were confirmed using a test where they listened to sounds and chose which color they associated with what they heard. The sounds were repeated in random order, so we could see if they were consistent in matching certain sounds with particular colors.”
The researchers then analyzed individual DNA samples looking for genetic clues. In each family, they spotted rare DNA changes that altered the way genes code for proteins. They also noted commonalities in the way synesthesthetic brains handle axonogenesis, the process that enables brain cells to wire up to their correct partners.
Tilot said that the research team hopes to expand the project to study less common forms of synesthesia.
“Some synaesthetes describe numbers, for example, as having specific personalities — this is called ordinal-linguistic personification,” she said. “In one rarer form, words can be connected to specific tastes, a type called lexical-gustatory synesthesia.”
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The researchers are also looking for more volunteers.
"Although we studied families where several people all experience the same form of synesthesia, there are lots of people who are synesthetic but don’t have a family history of synesthesia,” she said. “We’re currently studying hundreds of unrelated people who link colors with letters or numbers, to learn about the genetics of synesthesia from a different angle.”
Tilot invited readers to learn more about the study and take a short test if interested in participating in future research.