Modular headache theory.

Many people experience headaches that do not fulfil the International Headache Society's criteria for a specific headache disorder yet behave biologically like that disorder. Others fulfil criteria for one headache disorder and yet have features of another disorder. To explain these observations, we propose that groups of neurones called modules become activated to produce each symptom of a primary headache disorder, and that each module is linked to other modules that together produce an individual's headache. This theory has implications for the classification, research and treatment of primary and secondary headache patients.