Irritable bowel syndrome (IBS) is characterized by abdominal pain and altered bowel habits. Visceral hypersensitivity is believed to be a key underlying mechanism that causes pain.
There is evidence that interactions within the brain and gut axis (BGA) that involves both, the afferent-ascending and the efferent-descending pathways as well as the somatosensory cortex, insula, amygdala, anterior cingulate cortex and hippocampus are deranged in IBS showing both the activation and inactivation.
Clinical manifestations of IBS such as pain, altered gut motility and psychological dysfunction may each be explained, in part through the changes in the BGA but there is conflicting information and its precise role is not fully understood. A better understanding of the BGA may shed more knowledge regarding the pathophysiology of IBS that in turn may lead to the discovery of novel therapies for this common disorder.
Emeran Mayer from the University of California, Los Angeles, has been studying the connection between the gut’s microorganisms and our nervous system for years.
“Discovering structural changes in the brain, whether they are primary or secondary to the gastrointestinal symptoms, demonstrates an ‘organic’ component to IBS and supports the concept of a brain-gut disorder,”
The gastrointestinal (GI) tract has a unique neuronal innervation that includes both an intrinsic neural network called the enteric nervous system (ENS) and an extrinsic neural network with connections to the central nervous system (CNS) that provides sympathetic and parasympathetic innervation. The vagus nerve and its branches provide an important connection between the brain and the gut and convey both afferent and efferent information. These networks play a crucial role in the normal regulation and homeostasis of the GI tract.
Emotion plays a key role in altering autonomic and endocrine function which in turn may derange the emotional circuitry. In health, peripheral stimuli travel through the afferent pathways and before reaching the higher cortical regions, they are filtered and evaluated in the neocortical and subcortical regions in order to prevent a circuit overload. When the filtering process is altered, stimuli can reach emotional areas, which in turn activate deep brain structures leading to aberrant interpretation of symptoms. Consequently non-noxious stimuli can be misinterpreted as painful or harmful. How this filtering process becomes altered in IBS patients is not known.
New findings now suggest that early childhood trauma could be influencing how the microbes in our gut interact with our brains as we grow, demonstrating a two-way street between the development of our nervous system and the microscopic residents of our digestive system.