Are the periodic changes of neurophysiological parameters during the pain-free interval in migraine related to abnormal orienting activity?

Objective and methods: Migraine patients are characterized by increased amp litude and reduced habituation of contingent negative variation (CNV). Furt hermore, the CNV underlies periodic changes during the pain-free interval, being maximal before attack. The periodicity of CNV is related to periodic changes in habituation, probably due to variation of orienting activity dur ing the pain-free interval. CNV and orienting response (OR) were studied in 20 females suffering from migraine without aura and in 12 matched healthy females. The neurophysiological recordings in the group of patients were pe rformed 1-4 days before and 4 days after a migraine attack. The amplitudes and habituation of early and late components and total CNV were calculated. The OR was assessed using the habituation of the skin conductance response (SCR) and alpha blocking (AB). The non-parametric tests were employed for statistical analysis. Results: There were no differences between the two groups for habituation o f all CNV components and of SCR following an attack. However, the habituati on of AB was significantly reduced in migraine. Before attack we observed a significantly reduced habituation of the early and total CNV and of the AB compared to controls and recordings performed after an attack. The habitua tion of the late component and of SCR remained unchanged. Conclusions: The abnormal habituation could be explained by the periodic ch anges of physiological parameters during the pain-free interval. The impair ed habituation of early CNV in migraine is associated with increased orient ing activity seen only in the central component (AB) of OR.