A Swiss woman who fell off her bicycle has yielded a unique insight into how auditory hallucinations are generated.

The woman suffered damage to the part of the brain where speech is generated and could speak only in short, stunted words and sentences. Five months later, when she suddenly developed epilepsy, she began “hearing” voices with the same speech impediments as herself.

“She initially heard her own voice speaking aloud, then the voices of hospital staff,” says Daniela Hubl at the University Hospital of Psychiatry in Bern, Switzerland, a member of the team that treated her. “They had the same speech impediments as she did. It …