What is synesthesia and why do some people taste sounds or see music?

The answer

Synesthesia is a neurological condition where stimulation of one sense automatically triggers another. Approximately 4% of the population experiences some form: grapheme-color (seeing letters as specific colors) is most common, but over 80 types exist, including lexical-gustatory (words triggering tastes) and mirror-touch (feeling others' physical sensations). A 2018 study in the Proceedings of the National Academy of Sciences found synesthetes have measurably increased structural connectivity between brain regions, with extra white matter tracts linking sensory areas. The condition runs in families with 40% heritability. Renowned synesthetes include Pharrell Williams (who sees music as colors), Vladimir Nabokov, and Duke Ellington. Intriguingly, many young children show synesthetic responses that typically prune away by age eight.