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Fashion influences science just as much as any other human activity. When neurologist Richard Cytowic became interested in synaesthesia, colleagues told him it was “too New Age” and would ruin his career. People with this intriguing physiological phenomenon – about 1 in every 100,000 – experience the world as a sensory salad, “seeing” sounds and “tasting” shapes. The concept was first described in the 17th century, but by the late 20th century it was considered too weird for serious study. Ten years ago, Cytowic published The Man Who Tasted Shapes (Imprint Academic/MIT Press, £14.95/$19.95). That sparked a resurgence and his book has been updated to include the latest knowledge. It is a very readable description of something more than just a medical curiosity. Synaesthesia may shed light on the greatest of mysteries, the functioning of the human brain.