Visceral and cutaneous pain representation in parasylvian cortex

The ability to localize both touch and pain has been attributed mainly to the primary somatosensory cortex (S1), based on its fine somatotopic mapping of tactile inputs. Recently, S1 has also been implicated in the differentiation of noxious stimulation, such as distinguishing between pain arising from viscera and skin. Recent MEG and fMRI studies show that there is at least a rudimentary tactile topographic representation in the supra-sylvian cortex [encompassing secondary somatosensory area (S2)], suggesting that this area may contribute to touch localization. Nevertheless, the role of this region in pain localization or its role in the differentiation of various types of pain has not been clearly established. Healthy subjects (four males, three females) underwent fMRI-scanning (1.5 T, standard head coil, BOLD analysis) during painful balloon distention of the distal esophagus and painful heat on the midline chest in the zone of referred pain for the esophageal stimulation. Five of the seven subjects exhibited significant activation of the parasylvian region in both experimental conditions, and in each of these five subjects activation related to esophageal pain was represented more laterally within the parasylvian cortex than that associated with cutaneous trunk pain (paired t-test, p's < 0.01). Our results suggest segregation of visceral esophageal and cutaneous chest afferents within parasylvian cortex, possibly implicating this region in the perceptual differentiation of visceral and cutaneous pain.