Visual evoked potentials during long periods of pattern-reversal stimulation in migraine

We have previously shown that during repetitive pattern-reversal stimulation, lasting 2 min, the amplitude of the visual evoked potential (PR-VEP) increases in migraineurs when tested interictally whereas it decreases 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 maxima after 12 min, at a time when there is a decrease of stimulation-enhanced lactate levels in the occipital cortex. We have therefore compared PR-VEP during long periods of repetitive stimulation in healthy control subjects (n = 25) and in patients suffering from migraine without (n = 25) and with aura (n = 15) between attacks. During uninterrupted stimulation at 3.1 Hz VEPs were sequentially averaged in blocks of 100 responses for a total duration of 15 min and analysed in terms of latencies and peak-to-peak amplitudes of N1-P1 and P1-N2 peaks. Amplitude changes from the baseline were calculated for each block, by comparison with the first block, and analysed statistically using Zerbe's method. The N1-P1 and P1-N2 amplitudes in the first block tended to be lower in migraineurs than in healthy control subjects. During the 15 min of stimulation, amplitudes of both components progressively decreased in control subjects, but remained stable in both groups of patients. The difference between patients and control subjects proved to be significant (P < 0.05). The neurophysiological data were not correlated with clinical features such as attack frequency or duration of illness. These results are yet another demonstration in migraine of an interictal habituation deficit in cortical information processing, which might favour lactate accumulation in sensory cortices during sustained activation.