Brain-gut connections in functional GI disorders: anatomic and physiologic relationships

Understanding the neural regulation of gut function and sensation makes it easier to understand the interrelatedness of emotionality, symptom-attentive behavior or hypervigilance, gut function and pain. The gut and the brain are highly integrated and communicate in a bidirectional fashion largely through the ANS and HPA axis. Within the CNS, the locus of gut control is chiefly within the limbic system, a region of the mammalian brain responsible for both the internal and external homeostasis of the organism. The limbic system also plays a central role in emotionality, which is a nonverbal system that facilitates survival and threat avoidance, social interaction and learning. The generation of emotion and associated physiologic changes are the work of the limbic system and, from a neuroanatomic perspective, the 'mind-body interaction' may largely arise in this region. Finally, the limbic system is also involved in the 'top down' modulation of visceral pain transmission as well as visceral perception. A better understanding of the interactions of the CNS, ENS and enteric immune system will significantly improve our understanding of 'functional' disorders and allow for a more pathophysiologic definition of categories of patients currently lumped under the broad umbrella of FGID.