Inclusion Criteria for Controls.

• Healthy male (N=30) and female (N=30) volunteers aged 18-80 years.

• Having capacity to provide written informed consent before participating in the study.

• Able to communicate adequately with the investigator and to comply with the requirements for the entire study.

Inclusion Criteria for Constipated Patients.

• Male and female volunteers aged 18-80 years.

• Individuals with chronic constipation for 1 year, with 2 or more of the following symptoms for 3 months or longer: <3 bowel motions/week, straining ≥ 25% of time, hard or lumpy stools ≥ 25% of time, incomplete evacuation ≥ 25% of time, feeling of anorectal blockage ≥ 25% of time.

• Having capacity to provide written informed consent before participating in the study.

• Able to communicate adequately with the investigator and to comply with the requirements for the entire study.

Exclusion Criteria for Controls (Items indicated with an asterisk are also exclusion criteria for patients).

• Clinical evidence of significant cardiovascular, respiratory, renal, hepatic, gastrointestinal, hematological, neurological, psychiatric or other disease that may interfere with the objectives of the study and/or pose safety concerns.*

• Current symptoms of a functional gastrointestinal disorder assessed by questionnaire [2, 16].

• Putative risk factors for pelvic floor trauma: i.e. six or more vaginal deliveries, birthweight >4500gms (macrosomia), or known 3rd or 4th degree perineal tear.

• Medications that are likely to alter gastrointestinal motility: e.g., opiates, anticholinergic medications, serotoninergic agents, alpha adrenergic agonists, calcium channel or b blockers; a stable dose of thyroxine will be permitted (i.e. no alterations in dose for the preceding three months).

• Active rectal inflammation, cancer; perianal sepsis; history of pelvic radiation, rectosigmoid surgery or inflammatory bowel disease.*

• Anxiety or depression as assessed by the Hospital Anxiety and Depression Questionnaire [17].

• Contraindications for MR imaging: i.e. pacemakers, aneurysm clips, cochlear implants.*

• Pregnant women, prisoners and institutionalized individuals.*