Stress and anxiety from trauma, and the mind in general, can affect physiological responses. Hypnotherapy, mediation and a variety of other things illustrate this point.
Research suggests that IBS is caused by a physiological miscommunication in the complex gut-brain signaling processes.
There is physiological evidence illustrating that GI infection can cause 'post infectious IBS' that may or may not correct itself within 5 years. And there is further physiological evidence seen in the effect that the ebb and flow of hormones, composition of the colonic microflora and malabsorption of short chained carbohydrates have on the gut-brain communication processes.
There is no evidence that psychological experiences 'cause' physiological miscommunication producing IBS. However, there is evidence to suggest that psychological experience may precipitate IBS perhaps by exacerbating or modulating pre-existing gut-brain physiological miscommunication processes.
It is difficult, if not impossible, to show a direct causal relationships between negative psychological experiences and physiological gut-brain miscommunication to 'cause' IBS.
In many ways after you have IBS the cause is somewhat irrelevant. One's time is better focused on developing tools for managing the symptoms.
-------------------- STABLE: ♂, IBS-D 50+ years - Science of IBS