Investigation of Cortico-Rectal Pathways in Healthy Subjects and Constipated Patients

Biofeedback therapy improves bowel symptoms and anorectal function in patients with dyssynergic defecation, however its mechanism of action is not known. The investigators hypothesize that biofeedback therapy enhances gut-brain-gut communication by altering cortical processing of information and improving cortically mediated neuromuscular function of the gut. However, in order to better understand these mechanisms in patients, the investigators need to examine and establish normative data and compare findings with healthy subjects. The investigators specific aims are to examine and evaluate the following 40 normal subjects; (1) To evaluate the afferent cortical evoked potentials in response to the electrical stimulation of the anorectum and (2) To evaluate the corticofugal tracts (efferent) by recording the anal and rectal electromyographic responses following noninvasive lumbosacral and transcranial magnetic stimulation.