Dear Doctors: When our grandson first learned his colors, he sang them along with music. We thought he was copying that song for learning the ABCs. But when he got older, he started saying that he “hears” the colors. We have been told this is called synesthesia. How and why does it happen?
Dear Reader: Synesthesia is a somewhat rare and quite fascinating phenomenon. It’s a neurological condition in which sensory input gets cross-wired in the brain. The result is that incoming information that would ordinarily be interpreted by a single sense spills over and stimulates another unrelated sense. While this blending of the senses has been described and referenced throughout the centuries, the emergence of the word “synesthesia” dates back to the late 1800s.
For some people with the condition, sounds will also activate the vision centers of the brain. For others, colors can also have flavor, flavors can evoke a physical shape, numerals can have colors and reading printed words can elicit distinct aromas. Depending on how the senses combine, there may be as many as 60 different forms of synesthesia. Estimates of the number of people who experience some form of synesthesia range from as low as 1-in-20,000 individuals to as high as 1-in-23.
Another ongoing discussion, which has not been conclusively resolved, concerns whether the condition appears in women more often than in men. The audiovisual variety that your grandson has described is considered to be one of the more common forms. The rarest is known as lexical-gustatory synesthesia, which causes speakers to “taste” the words they are saying.
Someone is either born with synesthesia or develops the condition at an early age. The condition does not affect an individual’s general health, nor is it linked to any diseases or physical disorders. It’s important to note that, despite the very different way that someone with synesthesia experiences and processes the world, it is not a form of, or a sign of, mental illness. In fact, studies and anecdotal data suggest that people with synesthesia are often highly intelligent and perform better on memory tests than those who don’t have the condition. Interestingly, there is also some evidence that people with the condition may often have a poor sense of direction.
As for the cause, that remains unknown. From the time synesthesia was first named and described, researchers have been looking into its origins. Some suspect the sensory crossover occurs due to the presence of additional neurons, which may link the affected senses. Another theory involves changes to how the brain receives information, as well as how that information gets processed.
The condition has also been found to run in families. Up to 40% of people with synesthesia turn out to have a close relative who also has a form of the condition. This makes it likely that heredity and genetics play a role. Meanwhile, advances in imaging technologies continue to aid in synesthesia research. It’s quite likely that we’ll have more answers in the not-too-distant future.
(Send your questions to askthedoctors@mednet.ucla.edu. Owing to the volume of mail, personal replies cannot be provided.)
