Gender differences in cortical representation of rectal distension in healthy humans

Cerebral cortical processing of information relayed via visceral afferents is poorly understood. We determined and compared cortical activity caused by various levels of rectal distension in healthy male and female subjects. Twenty-eight healthy, young (20-44 yr) volunteer subjects (13 male, 15 female) were studied with a paradigm-driven functional magnetic resonance imaging (fMRI) technique during barostat-controlled rectal distension at perception threshold and 10 mmHg below and above perception threshold. Male subjects showed localized clusters of fMRI activity primarily in the sensory and parietooccipital regions, whereas female subjects also showed activity in the anterior cingulate and insular regions. A progressive increase in maximum percent fMRI signal change and total volume of cortical activity was associated with the intensity of rectal distension pressure in both genders. Regions of cortical activity for below-threshold stimuli showed less substantial signal intensity and volume than responses for threshold and above-threshold stimuli. Volume of cortical activity during rectal distension in women was significantly higher than that for men for all distensions. We conclude that 1) there are substantial differences in female cortical activation topography during rectal distension compared with males; 2) intensity and volume of registered cortical activity due to rectal stimulation are directly related to stimulus strength; and 3) rectal stimulation below perception level is registered in the cerebral cortex.