Abstract
Support is provided for a primary neural factor in migraine by studies in autonomic responsiveness to sensory stimuli in relation to the laterality of pain. Migraineurs with consistently lateralised headaches were found in two studies to exhibit extremes of autonomic responsiveness to sensory stimuli during the interictal phase. The direction of responsiveness was predictive of the laterality of pain; left-sided pain was associated with under-responsiveness and fast habituation, right-sided pain with over-responsiveness and slow habituation. Bipolarity in rate of habituation is consistent with a defect in a regulatory mechanism that controls regional cerebral activation such as the diffuse thalamic projection system.