Changes in cortical processing of pain in chronic migraine

The aim of this study was to perform a topographic and dipolar analysis of nociceptive-evoked responses obtained by laser stimulus under basal conditions in a cohort of chronic migraine (CM) patients, compared with migraine without aura (MWA) patients and noncraniofacial pain controls.

An increased activation of cortical areas devoted to the emotional and attentive components of pain was previously found during the course of the migraine attack; it was more pronounced in patients reporting higher frequency of migraine.

Twenty-six outpatients were enrolled in the study; 16 fulfilled the criteria of CM, and 10 were affected by MWA. Fifteen noncraniofacial pain subjects were also selected. The pain stimulus was a CO2 laser pulses. The right-supraorbital zone was stimulated. Source localization analysis was performed on the most prominent laser-evoked potentials (LEPs) peak (P2) for each data set. The anatomical locations of the P2 sources were projected onto a standard normalized 3D MRI model.

The CM group differed significantly from both MWA patients and controls for the x coordinate and from controls for the z coordinates. The P2 dipole localized in the rostral cingulate cortex in CM patients, lying in a more posterior location within the anterior cingulate cortex (ACC) in both controls and MWA patients. The x coordinate of the P2 dipole, expressing the postero-anterior location, was significantly correlated with frequency of headache.

CM seems to be characterized by a distinctive pattern of cortical elaboration of pain, with a prevalent activation of the rostral portion of the ACC: our results suggest that this may be a predisposing factor to migraine chronicity.