Visual evoked potentials in interictal migraine: no confirmation of abnormal habituation.

Objective: We intended to study the effect of check size on visual evoked potential habituation in interictal migraine, using the faster 3 per second reversal rate and an improved analytic procedure with block-number blinding.

Background: Habituation in migraineurs has been extensively studied with visual evoked potentials. Despite discrepant results, possibly related to the use of different stimulus conditions, lack of habituation in the period between attacks is presently considered to be a neurophysiological hallmark of migraine.

Methods: Midoccipital monocular visual evoked potentials were recorded and analyzed in 27 interictal migraineurs and 34 healthy controls using a blinded study design. Small 8' checks and large 65' checks were applied in random order, both with 3 reversals per second. Six consecutive blocks of 100 responses were recorded for each check size. N70-P100 and P100-N145 peak-to-peak amplitudes were measured. Regression slopes across the 6 blocks, supplemented by last block/first block ratio and repeated measures analysis of variance with amplitude as the dependent variable, were used to test for habituation.

Results: N70-P100 habituation to small and large checks was observed in controls (mean slope -0.30 and -0.11 μV/block) and interictal migraineurs (-0.32 and -0.26 μV/block). P100-N145 habituation to small checks in controls (mean slope -0.39 μV/block) and to small and large checks in interictal migraineurs (-0.38 and -0.17 μV/block) was also observed. None of the habituation measures were significantly different between healthy controls and migraineurs (F < 1.6, P > .18). The check-size effect was similar in the 2 groups (F < 2.3, P > .14).

Conclusion: Reversal rate and check-size differences do not seem to explain the discrepant visual evoked potential habituation results in the migraine literature. Furthermore, no differences in first block amplitudes or N70, P100, and N145 latencies between healthy controls and migraineurs were found. We recommend blinded evaluation designs in future habituation studies in migraine.