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 b y various levels of rectal distension in healthy male and female subjects. Twenty-eight healthy, young (20-44 yr) volunteer subjects (13 male, 15 fema le) were studied with a paradigm-driven functional magnetic resonance imagi ng (fMRI) technique during barostat-controlled rectal distension at percept ion threshold and 10 mmHg below and above perception threshold. Male subjec ts showed localized clusters of fMRI activity primarily in the sensory and parietooccipital regions, whereas female subjects also showed activity in t he anterior cingulate and insular regions. A progressive increase in maximu m percent fMRI signal change and total volume of cortical activity was asso ciated with the intensity of rectal distension pressure in both genders. Re gions of cortical activity for below-threshold stimuli showed less substant ial signal intensity and volume than responses for threshold and above-thre shold stimuli. Volume of cortical activity during rectal distension in wome n was significantly higher than that for men for all distensions. We conclu de that 1) there are substantial differences in female cortical activation topography during rectal distension compared with males; 2) intensity and v olume of registered cortical activity due to rectal stimulation are directl y related to stimulus strength; and 3) rectal stimulation below perception level is registered in the cerebral cortex.