Short latency cerebral response evoked by painful electrical stimulation applied to the human sigmoid colon and to the convergent referred somatic pain area

Background. The brain-gut interaction is important for the understanding of pain mechanisms related to gastroenterological diseases. Unfortunately little is known about the early cerebral events related to the processing of gut-evoked pain. The aims of this human study were (1) to investigate the early-evoked brain potentials (EPs) to painful sigmoid colon stimulation and (2) to evaluate the EPs evoked from the convergent referred skin pain area after this area was induced by the painful gut stimulation. The background for the second aim was to evaluate whether the convergent input between somatic and visceral structures could induce detectable short-term cortical reorganization. Methods. Eleven subjects (nine men) participated; the mean age was 39.5±11.9 years. The gut-evoked EPs (recorded from 31 scalp sites) were evoked by electrical stimulation 30 cm from the anal verge by a modified biopsy forceps, inserted through a sigmoidoscope. The painful gut stimulation elicited a characteristic pain pattern referred to the abdomen. The short latency somatosensory evoked potentials were evoked from the skin inside and outside the referred pain area elicited by gut stimulation. A total of 750 electrical stimuli were delivered to the gut at slight painful stimulus intensity and 500 stimuli were delivered to the skin. Results. Short-latency EPs to electrical gut stimulation with an onset of 50–60 ms could be recorded. The gut EP topography revealed three consecutive positive peaks (P63, P101, P145) towards the frontal area. Centroparietal negativities (N128 and N222) were found, which were followed by two central positivities (P269 and P352). The somatic and gut evoked EPs differed in morphology and topography, but the EPs to skin stimulation inside and outside the gut-evoked referred pain area did not differ significantly. Conclusion. Short latency (50–60 ms) EPs to painful electrical sigmoid colon stimulation were demonstrated, reflecting an early cortical processing of sensory input from the sigmoid colon. The early cortical processing of somatic input from experimentally evoked visceral referred pain areas did not cause any detectable short-term cortical reorganization.