VISUAL-EVOKED POTENTIALS DURING LONG PERIODS OF PATTERN-REVERSAL STIMULATION IN MIGRAINE

We have previously shown that during repetitive pattern reversal stimu lation, lasting 2 min, the amplitude of the visual evoked potential (P R-VEP) increases in migraineurs wizen tested interictally whereas it d ecreases in healthy control subjects. According to Sappey-Marinier et al. (J Cereb Blood Flow Metab 1992; 12: 584-92) habituation of the PR- VEP in normal subjects is maximal after 12 mil?, at a time when there is a decrease of stimulation-enhanced lactate levels in rite occipital cortex. We have therefore compared PR-VEP during long periods of repe titive stimulation in healthy control subjects (n = 25) and in patient s suffering from migraine without (n = 25) and with aura (n = 15) betw een attacks. During uninterrupted stimulation at 3.1 HZ VEPs were sequ entially averaged in blocks of 100 responses for a total duration of 1 5 min and analysed in terms of latencies and peak-to-peak amplitudes o f N1-P1 and P1-N2 peaks. Amplitude changes from the baseline were calc ulated for each block, by comparison with the first block, and analyse d statistically using Zerbe's method The NI-PI and P1-N2 amplitudes in the first block tended to be lower in migraineurs than in healthy con trol subjects. During the 15 min of stimulation, amplitudes of both co mponents progressively decreased in control subjects, but remained sta ble in both groups of patients. The difference between patients and co ntrol subjects proved to be significant (P < 0.05). The neurophysiolog ical data Mere not correlated with clinical features such as attack fr equency or duration of illness. These results are yet another demonstr ation in migraine of an interictal habituation deficit in cortical inf ormation processing, which might favour lactate accumulation in sensor y cortices during sustained activation.