All 106 individuals in the study were women - the selection wasn't completely random. By the ROME definition pain is associated with IBS irrespective of subtype so the 55 women with IBS had pain. Only 17 of the 55 were classified as pain-predominant - this is a very small size. A simple explanation could be that the normal individuals didn't have a cause of pain in the gut but the IBS individuals did. As I mentioned, in the original article the authors say they don't know if the change in grey matter in the cognitive pain region of the brain is due to primary alterations in brain or if they are a consequence of altered visceral signaling to the brain. This is an interesting study that adds significant to what is known but it still leaves the question as to the cause of IBS and associated pain a mystery.
-------------------- STABLE: ♂, IBS-D 50+ years - Science of IBS