Differential NMR spectroscopy reactions of anterior/posterior and right/left insular subdivisions due to acute dental pain

Abstract

OBJECTIVES: The insular cortex has an important role within the cerebral pain circuitry. The aim of this study was to measure metabolic alterations by MR spectroscopy due to experimentally induced trigeminal pain in the anterior/posterior and right/left insular subdivisions. METHODS: Sixteen male volunteers were investigated using magnetic resonance (MR) spectroscopy before, during and after experimentally induced dental pain. Biphasic bipolar electric current pulses of 1 ms duration were administered based on the subjectively determined pain threshold. Volunteers were instructed to rate every stimulus using a MR compatible rating scale. RESULTS: Due to the pain stimulation a significant absolute increase in glutamate (Glu, F = 6.1; P = 0.001), glutamine (Gln, F = 11.2; P = 0.001) as well as glutamate/glutamine (Glx, F = 17.7; P = 0.001) were observed, whereas myo-inositol (mI, F = 9.5;P = 0.001) showed a significant drop. Additionally, these metabolites showed a significant effect towards lateralisation, meaning that metabolic concentration differed either in left or right insular subdivision. Creatine demonstrated also an absolute significant decrease during stimulation (F = 2.8; P = 0.022) with a significant anterior-posterior difference (F = 40.7; P = 0.001). CONCLUSIONS: Results confirm that the insular cortex is a metabolically high active region in pain processing within the brain. Quantitative metabolic changes show that there is a distinct but locally diverse neurometabolic activity under acute pain. The known cytoarchitectonic subdivisions show different metabolic reactions and give new insights into pain-processing physiology. KEY POINTS: • Dental pain leads to recognisable changes in MR spectroscopy of the insula • Immediate changes in glutamate, glutamine, composite glutamine/glutamate and myo-inositol are seen • Sub-regions demonstrate different metabolic reaction patterns to acute trigeminal pain stimulation • Differing metabolic reaction patterns to acute trigeminal pain stimulation confirm cytoarchitectonic differentiation.