Intensity dependence of auditory evoked potentials is pronounced in migraine: an indication of cortical potentiation and low serotonergic neurotransmission?

Migraine is associated with stimulus hypersensitivity, increased evoked cortical responses, and abnormal 5-HT levels in peripheral blood. We studied cortical auditory evoked potentials (AEPs) between attacks in 35 patients suffering from migraine without aura (MO, n = 25) or with aura (MA, n = 10) and in 25 healthy volunteers. Binaural tones were delivered at 40, 50, 60, and 70 dB sensation level (SL) in a pseudorandomized order. The intensity dependence of the auditory N1-P2 component was significantly greater in MO (p = 0.003) and MA (p = 0.02) patients than in healthy controls, resulting in a much steeper amplitude/stimulus intensity function slope. When three sequential blocks of 40 averaged responses were analyzed at the 40- and 70-dB SL intensities, N1-P2 amplitude decreased in second and third blocks at both intensities in controls, but increased in migraineurs, a difference that was significant in both blocks for the 70-dB SL stimulus. The strong interictal dependence of AEPs on stimulus intensity may thus be due to potentiation (instead of habituation) of the response during repetition of the high-intensity stimulation. In concordance with previous studies of visual evoked potentials, these results confirm that migraine is characterized between attacks by an abnormality of cortical information processing, which might be a consequence of low 5-HT transmission and favor cortical energy demands.