Functional neuroimaging of visceral sensation

The use of functional brain imaging techniques has led to considerable adva nces in our understanding of brain processing of human visceral sensation. The use of complementary techniques such as functional MRI, positron emissi on tomography, magnetoencephalography, and EEG has led to the identificatio n of a network of brain areas that process visceral sensation. These studie s suggest that unlike somatic sensation, which has an intense homuncular re presentation in the primary somatosensory cortex (SI), visceral sensation i s primarily represented in the secondary somatosensory cortex, whereas repr esentation in SI is vague. This difference could account for the poor local ization of visceral sensation in comparison with somatic sensation. However , in a manner similar to that of somatic sensation, visceral sensation is r epresented in the paralimbic and limbic structures such as the insular, ant erior cingulate, and prefrontal cortices. These areas are likely to mediate the affective and cognitive components of visceral sensation. Recent studi es suggest that negative emotional factors such as fear, and cognitive fact ors such as attention can modulate the brain processing of visceral sensati on in the insular and anterior cingulate cortices. In addition, alterations in the pattern of cortical processing of visceral sensation have been desc ribed in patients with functional gastrointestinal pain. It is likely that future research into the factors that modulate the brain processing of visc eral sensation in health and disease are likely to improve further our unde rstanding of the pathophysiology of functional visceral pain disorders.