Irritable bowel syndrome (IBS) is a common digestive disorder that primarily affects the large intestine, also known as the colon. It may also be referred to as irritable colon, spastic colon, or spastic colitis. These disorders stem from problems in the brain and gut interaction. For instance, the neurotransmitter serotonin plays a role in the brain and the digestive system. Conditions like anxiety, depression, stress, and sleep disturbances, such as insomnia, can contribute to IBS development in some instances.