The only intra cranial structures innervated by sensory nerves, and therefore a possible source of the headpain are the meninges and the large intracerebral arteries. The dilatation of the cerebral vessels may not be the origin of the head pain per se, but measurements of the intra cerebral vascular bed in the past has proven valuable in the migraine-research, and has helped elucidate the basis for the migraine aura (Olesen, Friberg et al. 1990). The effects of different signal molecules on the intra cerebral vasculature continue to be an important field in the migraine research, in the search for possible pain causing signaling molecules.