The investigators are testing the effect of electrical stimulation of the rectum on colonic motility. Most individuals with spinal cord injury develop neurogenic bowel dysfunction, which includes slowed colonic motility, which means that stools take longer than normal to pass through the colon. This slowed movement may result in chronic constipation and difficulty emptying the bowels. Individuals typically (without or without caregiver assistance) insert a gloved finger into the rectum and gently stretch it to improve colonic motility for a brief period to empty the bowels. The investigators hypothesize that electrically stimulating the rectum, instead of mechanically stretching it, will produce the same beneficial effect of improving colonic motility. Therefore, this study will compare the two methods. If electrical stimulation effectively improves colonic motility, then the investigator shall develop the approach as a therapeutic intervention in future studies.