Migraine, a word of French origin, is a mediaeval corruption of the Greek hemicrania". Its etymological meaning, half-headache, indicates two important features of the disorder, the headache and its onesidedness. In classical migraine, the headache is preceded by an 'aura' of focal neurological symptoms. The symptoms are generally sensory in nature and often involve disturbances of vision, such as scotomas, either dark or luminous, or the. scintillating scotoma, also called teichopsia, a phenomenon which will be described further in Chapter 3.2. There may also be a sensation of tingling, like 'pins and needles', which often commences in the fingers of one hand, gradually extending up the arm to jump, at a given moment, to the area of the mouth. When this sensory disturbance affects the right side of the body, it may be associated with an aphasic disturbance of speech". However, the classical form of migraine occurs much less frequently than the so-called common migraine in which the headache comes on without an aura. Except for the presence of an aura in the former, classical and common migraine do not differ essentially from each other141 and therefore have been placed under the same nosological entity, migrai~e. The observations on the migraine attack which will be reviewed in. this section, can be roughly subdivided into three groups, i.e., those concerning (i) the circulation of the head, (ii) the gastrointestinal tract and (iii) the chemistry of the body. The circulation of the head - the cephalic circulation - can be subdivided into two compartments, the circulation of the brain - the cerebral circulation - and the circulation of the remaining structures of the head which is here referred to as the cranial circulation. The two parts of the cephalic circulation will be considered separately because of their distinct significance in the pathophysiology of the migraine attack