Transient neurological symptoms in full awareness allow us to understand functional brain organisation at first hand. Indeed, descriptions provided by patients or their families are usually accepted as adequate evidence to localise the side of brain dysfunction during transient ischaemic attacks and partial epilepsies.

Language is lateralised to the left cerebral hemisphere in most right-handed individuals, and crossed aphasia (that is, a language disorder secondary to a right hemisphere lesion in a dextral pertson) is a rarity (1–4%) in otherwise healthy subjects.

Over the past 10 years, as a result of my interest in headache and behavioural neurology, I have observed five patients with crossed aphasia during migraine auras. Patients were examined in an outpatient clinic, and systematically recorded. None of them had any factor that could account for an atypical dominance for language—that is, all patients were right handed, with no personal or family history of left-handedness, previous brain injury, epilepsy, developmental language disorders or learning disabilities. All had normal imaging examinations (MRI of brain in three and CT scan in two subjects) that excluded a structural lesion. Patients were contacted by telephone in 2005–6. The International Classification of Headache Disorders, second edition …