Cortical processing of human somatic and visceral sensation

Somatic sensation can be localized precisely, whereas localization of visce ral sensation is vague, possibly reflecting differences in the pattern of s omatic and visceral input to the cerebral cortex. We used functional magnet ic resonance imaging to study the cortical processing of sensation arising from the proximal (somatic) and distal (visceral) esophagus in six healthy male subjects. Esophageal stimulation was performed by phasic distension of a 2 cm balloon at 0.5 Hz. For each esophageal region, five separate 30 sec periods of nonpainful distension were alternated with five periods of simi lar duration without distension. Gradient echoplanar images depicting bold contrast were acquired using a 1.5 T GE scanner. Distension of the proximal esophagus was localized precisely to the upper chest and was represented i n the trunk region of the left primary somatosensory cortex. In contrast, d istension of the distal esophagus was perceived diffusely over the lower ch est and was represented bilaterally at the junction of the primary and seco ndary somatosensory cortices. Different activation patterns were also obser ved in the anterior cingulate gyrus with the proximal esophagus being repre sented in the right midanterior cingulate cortex (BA 24) and the distal eso phagus in the perigenual area (BA32). Differences in the activation of the dorsolateral prefrontal cortex and cerebellum were also observed for the tw o esophageal regions. These findings suggest that cortical specialization i n the sensory-discriminative, affective, and cognitive areas of the cortex accounts for the perceptual differences observed between the two sensory mo dalities.