O45: Lateral inhibition in somatosensory cortex of migraine without aura patients between attacks

Our objective was to investigate lateral inhibition within the somatosensory cortex in a group of migraine without aura (MO) patients compared to healthy volunteers (HVs) by stimulating two peripheral nerves simultaneously, while recording somatosensory evoked potentials (SEPs). SEPs were elicited by electrical stimulation of the right median and ulnar nerve at the wrist separately and simultaneously (300 sweeps per condition), in 21 MO patients between attacks and in 17 HVs. We measured parietal N20–P25 amplitudes and we evaluated the ratio ICLI = MU/(M + U) ∗ 100, where MU is the SSEP amplitude obtained simultaneously stimulating both median and ulnar nerves (MU), and M + U is the sum of amplitudes obtained by stimulating each nerve separately (M + U). Habituation was calculated as the slope of the linear regression between the 1st and the 3rd block of 100 averaged sweeps. SSEP N20–P25 amplitudes lack of habituation in MO patients ( p  = 0.03). On grand-average, ICLI resulted similar between groups. However, only when data of HV and MO patients were combined the habituation slope was positively correlated with ICLI ( r  = 0.331, p  = 0.04). These results suggest that lateral inhibitory mechanisms within somatosensory cortex may contribute to induce interictal lack of habituation of N20–P25 SSEPs amplitude seen in migraine patients.