Cerebral cortical representation of external anal sphincter contraction: effect of effort

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. Our aims were to determine the cortical areas associated with voluntary EAS contraction and to determine the effect of two levels of sphincter contraction effort on brain activity. Seventeen asymptomatic adults (ages 21-48, 9 male) were studied using functional magnetic resonance imaging (fMRI) to detect brain activity. Studies were done in two stages. In stage 1 (10 subjects, 5 male), anal sphincter pressure was monitored from a catheter-affixed bag. Subjects performed maximal and submaximal EAS contractions during two fMRI scanning sessions consisting of alternating 10-s intervals of sustained contraction and rest. In stage 2 studies, seven subjects (4 male) performed only maximum effort sphincter contractions without a catheter. EAS contraction was associated with multifocal fMRI activity in sensory/motor, anterior cingula...