Possible representation of somatic pain in the rat insular visceral sensory cortex: a field potential study

Vagus nerve stimulation evokes a potential in the dorsal insular cortex in rats. To determine whether this cortical visceral area, like the brainstem visceral nuclei, also receives somatic input, somatic potentials were examined. Subcutaneous electrical stimulation, regardless of the laterality and site, evoked a potential closely resembling the vagal potential in shape, surface distribution and depth profile. This somatic potential had a higher threshold and a longer latency than the potentials in the nearby somatosensory cortices, and was attributed to primary Adelta afferents based on conduction velocity measurements and the relationship to peripheral nerve activity. No Abeta afferent-related response was found. These results suggest that the insula receives convergent sensory input from both the viscera and body surface, and the latter probably conveys somatic nociceptive information.