Background: Absence of habituation during VEP measurements has extensively been studied in patients with migraine [1,2]. It is unclear whether this electrical phenomenon is accompanied by hemodynamic anomalies. In healthy controls, EP-habituation is well-known and hemodynamic refractory effects are observed in the net BOLDresponses to repetitive visual stimuli [3], i.e. a decreased amplitude and increased latency in time-to-peak for interstimulus intervals less than 6 seconds. Interictal hemodynamic differences between patients with migraine without aura and healthy controls have not been investigated. Methods: In this study, we measure interictal hemodynamic responses with functional magnetic resonance imaging in patients with migraine without aura and compare them with responses from healthy controls. Net responses to paired visual stimuli with varying interstimulus intervals are calculated. Several characterizing parameters of the responses are quantified. ANOVA and post-hoc Bonferroni tests are used for statistical analysis (significance level = 0.05). Results and discussion: Refractory effects are not observed in patients. There is no amplitude decrease, nor increased latency in time-to-peak in patients, not even for the shortest interstimulus interval, whereas in controls, refractory effects are found for all parameters of the net responses for an interstimulus interval of 1 second (amplitude and time-to-peak: p<0.001; width: p<0.01). The nonlinearities (i.e. differences in measured vs. expected responses) fade away with longer interstimulus intervals and have disappeared at the interstimulus interval of 6 seconds. The absence of refractory effects in patients with migraine without aura reflects the neurovascular correlate of the absence of habituation in this patient group. Multi-modal data acquisition (VEP/fMRI) or follow-up of patients taking prophylactic drugs may be subject to further research. References [1] Schoenen J. et al. (1995). Eur J Neurol 2(2): 115–22; [2] A ´ fra J. et al. (1998). Brain 121(2): 233–41; [3] Huettel S. A. and McCarthy G. (2000). NeuroImage 11(5): 547–55.