M1299 Endogenous Pain Modulation and Brain Activity in Irritable Bowel Syndrome (IBS) and in Healthy Controls: Individual Correlations During FMRI

Abstract

INTRODUCTION: A majority of patients with IBS show abnormal visceral and somatic sensory function and endogenous pain modulation compared to controls (Wilder-Smith C et al. World J Gastro 2007). While pain inhibition is evident in over 90% of controls, over 50% of IBS patients show pain facilitation and most of the remainder have decreased pain inhibition during heterotopic stimulation for activation of pain modulation. METHODS & AIMS: In this study we correlated individual pain intensities with individual fMRI brain activations in 14 female IBS (7 IBS-D, 7 IBS-C) and 14 female healthy subjects using electrical hand pain (pain threshold+20%) and foot cold pain (4°C) applied either alone or together (heterotopic stimulation). Hand stimulation below perception threshold was applied for control purposes. Six imaging runs (6x30s stimulation blocks) were presented in randomized sequence. Group-level activation maps using random effects general linear model with conditions of interest were generated via the finite impulse response (FIR) deconvolution method and corrected using cluster threshold estimation. RESULTS: After correction for multiple testing, there was a correlation in the change in hand pain during heterotopic stimulation and brain activation in the left anterior cingulate cortex ACC (BA 24), right ACC (BA32), right anterior insula and the right dorsolateral prefrontal cortex (BA9) during subliminal stimulation (p 0.60) in controls, but not in IBS. In IBS, but not controls, hand pain during endogenous painmodulation correlatedwith the changes in brain activation in the right ACC (BA32), left ACC (BA24) and PAG during heterotopic stimulation (p 0.55). If all subject data were pooled, individual pain ratings and brain activations correlated in the rostral ventromedial medulla, PAG, left and right amygdale, left putamen, right dorsolateral prefrontal cortex and the right precentral gyrus. CONCLUSIONS: Individual correlations of pain ratings and brain activations within the homeostatic modulatory network show significant differences between healthy and IBS subjects, both during subliminal stimulation and activation of endogenous pain modulation. There is consistent evidence for a shift in the dynamic balance between inhibition and facilitation.