Ask the Doctors: People with synesthesia might hear colors or taste words

Dear Doctors: When our grandson 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 he “hears” the colors. We have been told this is called synesthesia. How and why does it happen?

Answer: Synesthesia — a somewhat rare and quite fascinating phenomenon — is a neurological condition in which sensory input gets crosswired in the brain.

The result is that information that would ordinarily be interpreted by a single sense spills over and stimulates another unrelated sense.

This blending of the senses has been described for centuries. The word synesthesia dates to the late 1800s.

For some people with the condition, sounds also activate the brain’s vision centers. For others, colors can also have flavor, flavors can evoke a shape, numerals can have colors, and reading printed words can elicit aromas.

Depending on how the senses combine, there could be as many as 60 forms of synesthesia. Estimates of the number of people who experience some form of it range from as low as one in 20,000 to as many as one in 23.

The audiovisual variety your grandson has described is considered one of the more common forms. The rarest — lexical-gustatory synesthesia — causes speakers to taste the words they are saying.

Someone is either born with synesthesia or develops the condition at an early age.

It doesn’t affect health, nor is it linked to any disease or physical disorder, nor is it sign of, mental illness. Studies and anecdotal data suggest that people with synesthesia often are highly intelligent and perform better on memory tests than others.

There’s also evidence that people with the condition often have a poor sense of direction.

The cause is unknown. From the time synesthesia was first described, researchers have been looking into its origins. Some suspect the sensory crossover occurs due to the presence of additional neurons.

The condition has been found to run in families. Up to 40% of people with synesthesia turn out to have a close relative who has a form of the condition. This makes it likely that heredity and genetics play a role.

With advances in imaging technologies, it’s likely we’ll have more answers in the not-too-distant future.

Dr. Eve Glazier and Dr. Elizabeth Ko are internists at UCLA Health.