The external anal sphincter (EAS) plays a critical role in maintaining fecal continence, however, cerebral cortical control of voluntary EAS contraction is not completely understood. AIMS: 1) To determine the cortical areas associated with voluntary EAS contraction. 2) To determine the effect of two levels of sphincter contraction effort on brain activity. METHODS: Seventeen asymptomatic adults (age 21-48, 9 male) were studied using functional magnetic resonance imaging (fMRI) to detect brain activity. Studies were done in two stages. In stage one (10 subjects, 5 male), anal sphincter pressure was monitored from a catheter-affixed bag. Subjects performed maximal and sub-maximal EAS contractions during two fMRI scanning sessions consisting of alternating 10-second intervals of sustained contraction and rest. In stage two studies, seven subjects (4 male) performed only maximum effort sphincter contractions without a catheter. RESULTS: EAS contraction was associated with multifocal fMRI activity in sensory/motor, anterior cingulate, pre-frontal, parietal, occipital and insular regions. Total cortical activity volume was significantly larger (p<0.05) for maximal (5175±720 µL) compared to sub-maximal effort contractions (2558±306 µL). Similarly, percent fMRI signal change was significantly higher (p<0.05) for maximal (4.8±0.1%) compared to sub-maximal effort contractions (2.2±0.1%). Cortical region-of-interest analysis showed the incidence of insular activation to be more common in woman compared to men. Other cortical regions showed no such gender differences. FMRI activity detected in stage 2 showed similar regions of cortical activation to those of the stage 1 study. CONCLUSIONS: Willful contraction of the EAS is associated with multifocal cerebral cortical activity. The volume and intensity of cerebral cortical activation is commensurate with the level of contractile effort.