Prediction of migraine attacks using a slow cortical potential, the contingent negative variation.

Amplitudes of contingent negative variation (CNV) as a slow cortical potential in migraine patients were recorded before and after migraine attacks. The level of CNV amplitudes, especially of the early component, showed a trend in rise of negativity 1 day before the attack, whereas amplitudes were normal for 2-3 days following an attack. In most cases the attack occurred when the CNV amplitude showed maximum negativity. We conclude that migraine-susceptible days are indicated by a high CNV amplitude the day before the attack.