Migraine is a reversible brain dysfunction characterized by pain and passive coping strategies consistent with sickness behaviour. The brain contains no pain fibres and the only way it may signal pain is through the trigemino-vascular system. Here, it is postulated that migraine is an example of genetically determined behavioural responses and that sickness behaviour, a pan-mammalian adaptive response to internal and external stressors, characterizes the migraine attacks. Sickness behaviour is manifested in withdrawal and motor quiescence, sympatho-inhibition and lethargy, in which visceral pain signals a homeostatic imbalance of the brain. The sickness behavioural response is associated to pain felt as inescapable visceral pain, and depends upon brain networks involving different brainstem, hypothalamus and forebrain regions, that encode evolutionarily conserved adaptive genetic responses. This hypothesis, still speculative, may offer a more coherent view of migraine as an adaptive biobehavioural response triggered by a threatened brain.