Imagine hearing Bach every time you bite into a broccoli head. It might seem like the result of eating a questionable vegetable, but for synesthetes, it’s an everyday reality.
Synesthesia is a neurological phenomenon that causes "crossed" links between sensory experiences, and yes, it sounds like the stuff of comic books. You might have it if reading these letters brings a certain hue to mind, for example, or certain sounds trigger certain colors.
New research has identified genetic clues that could explain the biology of synesthesia, suggesting certain genes might predispose people to the condition.
Researchers analyzed the DNA of three families that had multiple synesthetes over several generations who experience color when listening to sound. Genome sequencing identified 37 possible gene variations that could be responsible for this phenomenon. While different in each family, these variants provide a common theme.
Six of the variants are related to axonogenesis – how neurons develop and connect to one another in the brain – suggesting an unusually high degree of connectivity in certain brain regions might predispose people to synesthesia.
Physical senses (sight, hearing, taste, smell, and touch) are separated into distinct experiences and work in specialized regions in the cerebral cortex. Brain scans show that when people “hear” color activity both sight and sound areas are highlighted.
Derived from the Greek meaning “to perceive together,” synesthesia links these sensory experiences. Stimulation of one sense provokes a secondary one through a unique “cross-talk” between different neurons in the brain.
"Brain imaging of adults with synaesthesia suggests that their circuits are wired a little differently compared to people who don't make these extra sensory associations. What we don't know yet is how these differences develop," said Dr Amanda Tilot, a geneticist at the Max Planck Institute for Psycholinguistics, in a statement. "We suspect some of the answers lie in people's genetic makeup."
Published in PNAS, the study suggests shared genes might influence brain development, leading to altered structural and functional connectivity in the brain. Researchers say it might offer a better understanding of autism, which also shares certain phenotypic characteristics with synesthesia.
Synesthesia was first reported more than 100 years ago, but genetic studies are still in their early stages and researchers say they were limited by the lack of past research. Information about synesthetes is also limited: some research suggest one in 2,000 people have synesthesia, others suggest as much as one in 500.
Researchers hope to expand the small sample size and correct these limitations by furthering their research. If this sentence looks red or green to you, find out how to get involved here.