Brain activity in rectosigmoid pain: Unravelling conditioning pain modulatory pathways

ObjectiveConditioning Pain Modulation (CPM) represents the various descending inhibitory mechanisms induced by a heterotopic noxious stimulation (previously termed DNIC). CPM-induced modulations in brain activity have not previously been investigated to visceral pain. Hence the aims were to assess the role of CPM in terms of: (1) psychophysics, (2) alterations in topography and amplitudes of evoked brain potentials and (3) modelling the brain activity.MethodsFifteen healthy volunteers were stimulated electrically in the rectosigmoid, and 64-channel brain activity was recorded two times before (reproducibility), during and after induction of CPM by immersing the non-dominant hand into water at 2 °C for 180 s (cold pressor).ResultsDuring CPM pain scores were reduced in comparison to baseline (P ⩽ 0.001), which corresponds to 30% pain attenuation. In comparison to baseline significant differences in bipolar EEG topography were seen during CPM, where N2 moved from central to frontal activity (P < 0.001), and peak-to-peak amplitude of the central N2–P2 complex measured at the Fz-electrode was enhanced (P = 0.04). Furthermore, dipolar source modelling showed an anterior shift of the mid-line cingulate dipole (P = 0.004) and a caudo-posterior shift of the insular dipole (P = 0.01) during CPM.ConclusionsA visceral platform was established to reliably assess the role of CPM, which for the first time demonstrated dynamic changes in cortical processing of visceral pain before, during and after CPM induction.SignificanceThe model provides a unique approach to study basic pain and pharmacological intervention in healthy volunteers as well as in patients with dysfunctional pain inhibition.

► Conditioning Pain Modulation (CPM) induced visceral pain attenuation.
► Evidence of topographic shift to frontal brain activity and enhanced amplitudes during CPM.
► Source localisation showed frontal shift of cingulate activity, possibly indicating enhanced anterior cingulate cortex (ACC) activation during CPM.