Cerebral hemisphere function and migraine.
An hypothesis that migraine is the experience of a protective vascular response to cerebral information overload has been explored to a limited extent by examining the association between laterality of the attack and verbal and spatial performances under standard symptom-free conditions. The study was restricted to individuals with unilateral symptoms always presenting on the same side. It emerged that those with classical migraine do not always have prodromata referable to the same side as the pain. Indeed, in the present study, prodromata were almost exclusively referable to the left (dominant) cerebral hemisphere. A subgroup of those with speech disturbances as a feature of the prodromal symptoms was also found to have relatively impaired language abilities on routine testing. It is this finding that lends some support to the hypothesis. The findings also invite the refining proposition that information overload, as defined in the hypothesis, is almost always borne by the dominant (verbal) hemisphere in our species. Such overload might concurrently or sequentially also overtax a suggested limited right hemisphere language capacity, in terms of the hypothesis, accounting for the right-sided pain sometimes presenting in these cases. Otherwise, pain appears to be predominantly left-sided or midline. Perhaps the frequency of this particular syndrome is an indictment of the limitations of language as a basis for communication, as well as reflecting the possibility that most of our stressful transactions and their cerebral processing use a verbal substrate. The results also reveal the need for agreement on rules for classification of laterality in migraine.