Actually there were issues left out of the video he did not cover. Like an alter gastro colonic responce to eating.
Most of the time when you here the vicious cycle in IBS it refers to "symptoms=anxiety=symptoms." What he was going into was the psychophysiology mechanisms. I am not sure if you caught it in the video, but the strongest evidence has to do with serotonin release from cells in the gut.
You should watch all these videos and especially this one.
Video Corner: Serotonin
Increasingly our understanding of IBS is that it is a heterogeneous disorder – that is, multiple factors contribute to the well defined symptoms of the disorder. One of these suspected underlying dysfunctions involves serotonin, which is a neurotransmitter or messenger to nerves. Most serotonin in the body is in cells that line the gut where it senses what is going on and through receptors signals nerves that stimulate a response. The serotonin must then be reabsorbed (a process called re-uptake) into cells. This process appears to be disrupted in people with IBS.
Serotonin and SERT How does serotonin affect gut function? An interview with Gary M. Mawe, PhD, Professor of Anatomy and Neurobiology, University of Vermont, Burlington, VT. Dr. Mawe is a basic scientist.
But this is the thing, its not a question anymore of the brain or gut brain, its recognizing and incorporating the functioning of both. Both are operational to cause the symptoms.