As compared to visceral pain, somatic pain is a much more developed area. Indeed, somatic afferents can be precisely investigated using a series of stimulation techniques that allow a selective activation of specific pathways (15,16). Some of these techniques can also be adapted for visceral stimulation.
Transmucosal electrical nerve stimulation has been applied in the gut via intraluminal electrodes mounted over a tube (5,6,17-21). Whereas distending stimuli activate sensory pathways and induce perception by specific stimulation of mechanoreceptors on the gut wall, trans-mucosal nerve stimulation induces similar perception by nonspecific stimulation of afferent pathways, that is, without relying on any specific receptor (5,6).
Methods for thermal stimulation, involving both cold and warm stimuli, have also been developed to test visceral afferents (22). Thermal stimulation of the gut can be produced via intraluminal bags by recirculating water at adjusted temperatures. It has been shown that the stomach and the intestine exhibit similar stimulus-related thermal sensitivity, but still gastrointestinal thermosensitivity in humans, and specifically the type of afferents activated by warm and cold stimuli, remain poorly explored. Nevertheless, thermal stimuli are potentially applicable in conjunction with mechanical and electrical stimuli for the evaluation of sensory dysfunctions of the gut. These combined techniques may help to identify the specific pathways affected and the level of the dysfunction.
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