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.
In this study, researchers from the United States determined the cortical areas associated with voluntary EAS contraction. They also evaluated the effect of 2 levels of sphincter contraction effort on brain activity.
The team studied 17 symptomatic adults (aged 21 to 48 years, 9 male) using functional magnetic resonance imaging (fMRI) to detect brain activity.
The study was performed in 2 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, 7 subjects (4 male) performed only maximum effort sphincter contractions without a catheter.
The team found that EAS contraction was associated with multifocal fMRI activity in sensory/motor, anterior cingulate, prefrontal, parietal, occipital, and insular regions.
They determined that total cortical activity volume was significantly larger for maximal compared with submaximal effort contractions.
Percent fMRI signal change was significantly higher for maximal compared with submaximal effort contractions.
The researchers found that cortical region-of-interest analysis showed the incidence of insular activation to be more common in women compared with men. Other cortical regions showed no such gender differences.
Dr Mark Kern's team concluded, "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".