IBS Part 2: Neurogastroenterology

While IBS is not considered to be as severe a condition as inflammatory bowel disease, it certainly remains a complex one. If we dive into the medical history books from the 20th Century alone, we find that the thinking of gastrointestinal doctors and scientists went through quite an evolution. Their observations of digestive function started off not only with collecting data about just what our insides were doing, but also how they were affected by our emotional states—stimulated either by what was happening to the patients being observed, or by something they were processing internally. By the middle of the century, the study of emotions was abandoned in favor of studying mechanical processes that the body underwent, and IBS was left to the realm of psychologists—even being questioned as to whether or not it even existed as a true medical condition. Eventually, the medical community came to recognize IBS as both real and treatable, to a greater or lesser extent.

One of the leading international organizations working today to educate doctors about IBS is the Rome Foundation. Founded in Rome, Italy in the 1980’s (hence the name), the Foundation has worked to properly identify and guide treatment for a whole host of conditions similar to IBS, collectively called functional gastrointestinal disorders, or FGIDs for short. The field that they have helped shape in studying these illnesses is called neurogastroenterology—meaning the study of the interaction between the gut and the brain, and how this relationship affects digestive function. Another way of framing this is that the medical community at large has been using a framework, informed by data collection and scientific inquiry, to view the body as a whole. As the Rome Foundation themselves have pointed out in their publications, this is in line not only with the traditions of Chinese medical thought, but also with its roots with the Greeks and Romans.

Neurogastroenterology, the gut-brain/gut-brain-microbiome axis, or even the mind-body-spirit connection—these are all terms describing the intimate and intricate ways in which the whole body seems to function as a single unit. Modern science has brought about remarkable insight into how our brains work, how little we know about them, and then more recently has elucidated how much we don’t know about our second brain center—namely our guts and the bugs that inhabit them. We have neural connections all throughout the GI tract, neurotransmitters sending signals from the brain down to the guts, and back again—called “wired and wireless connections” by some—and then we have our friendly bacterial, viral and fungal companions modulating those signals. So, if we take as a given that the mind is intimately intertwined with the gut and how it functions, the question then becomes how they are connected.

Let’s take the brain-gut axis to start. Borrowing the “wired and wireless” analogy for communication between the brain and the gut, let’s start with the wired form. The vagus nerve, also known as the “wanderer nerve” because of how long it is, travels from the brain all the way down, deep into the abdomen. It plays a vital role in our body’s parasympathetic nervous system, which is our “Rest and Relaxation” mode. It is also vital in sending information from our gut to our brain, and back down again.

As most of the vagus nerve’s fibers are dedicated to bringing information to the brain for data processing, the health of one’s brain will determine how well it is able to process and handle said data. Research seems to indicate that decreased size of parts of the brain that process signals coming from the gut, can reduce the subject’s ability to cope with these signals, and in turn increase visceral pain perception and sensitivity.

If we take a closer look at our wiring, then we see that the wire connecting the brain to the gut—the vagus nerve—is interfacing with the gut’s own nervous system, called the enteric nervous system, or ENS, which innervates the viscera and bowels—ie, our digestive organs—of the gut. The primary functions of the ENS are to help regulate blood flow, movement of the intestines (otherwise known as motility), secretion, how well they absorb nutrients and fluids, etc.

Because of all that is involved, the ENS has approximately 100 million neurons (for comparison, the human brain has around 100 billion neurons). These neurons are constantly receiving and transmitting information about what is happening in the gut to the brain via the vagus nerve, which in turn sends signals back down to the tissues in the gut and/or releases hormones to help maintain homeostasis, or balance. While conscious perception of what is occurring in the gut are not the primary functions of the neurons in the ENS, there are some neurons that may become altered in the presence of injury or inflammation. This can lead to noticeable feelings of abdominal, or visceral pain, which is a hallmark symptom of IBS.

The wireless forms of communication include activation of hormones, which are essentially messengers being sent from one part of the body to another to cause a chain reaction. Common and relatively benign hormones sent up to the brain from the gut include ghrelin, which is a hormone that informs the brain that the stomach is empty and it is hungry.

More complex chain reactions occur in the face of life stressors, either real or imagined—namely, the hypothalamus-pituitary-adrenal axis (or HPA axis, for short). This is particularly relevant to IBS sufferers, as this negatively affects their condition.

Such a chain reaction can basically unfold in this kind of scenario:

  1. Person X experiences stress after being yelled at by the boss.

  2. The hypothalamus, in the brain, releases a hormone, corticotropin-releasing factor (CRF), which sends a message to;

  3. The (anterior) pituitary, which is also in the brain. It makes its own message in the form of adrenocorticotropic hormone (ACTH), which is sent express mail all the way down to;

  4. The adrenal glands, which in turn release cortisol into the system.

  5. “Fight or flight” mode (AKA switching over to using our sympathetic nervous system) is now fully activated, although it doesn’t usually involve Person X taking a knife to the boss’s jugular or running screaming out of their office. It usually becomes internalized, meaning that the hormone cortisol isn’t being used for productive means, but rather to cause bowel sensitivity and pain, weight gain, or maybe a little bit of both.

While psychological stress has not been found to be the direct cause of any particular disease, it has been generally found to be bad for health—when experienced in excess. According to research done over the past few decades, stress can “blunt the sort of pain you feel in your skin and skeletal muscles while increasing the sensitivity of internal organs like the intestines to pain.” (Robert Sapolsky. Why Zebra’s Don’t Get Ulcers. New York, St. Martin’s Griffin, 2004: 82.)

Similar to other chemical processes that occur in the body, cortisol actually provides a useful function in the body. It is a steroid hormone that is, under normal circumstances, higher in the morning shortly after waking up, and lowers throughout the day. According to the Society for Endocrinology, cortisol’s “effects include controlling the body’s blood sugar levels and thus regulating metabolism, acting as an anti-inflammatory, influencing memory formation, controlling salt and water balance, influencing blood pressure and helping development of the foetus.” When the body releases excessive amounts on a frequent basis, however, it can lead to high blood pressure, excessive abdominal fat, anxiety and depression, and metabolic changes that can include development of type 2 diabetes. It is again important to note that while stress may not be the direct cause of this occurring, improper management of stress over a long period of time may lead to this kind of hormonal imbalance.

It is important to note that not everyone deals with the same kind of stress in the same way. Part of this is influenced by stress experienced early in life, usually in the form of childhood trauma. Early life stress, sometimes in the form of abuse, has been found to be a contributing risk factor for IBS later in life. What is postulated is that the early life exposure to trauma affects the brain’s ability to respond to stress later on in life, causing it to “overreact.” This reaction is the nervous system turning on its “fight or flight” mode, ultimately resulting in a heightened sense of anxiety —and in this case the anxiety revolves around the basic physical function of moving your bowels, which in turn feeds back to having that function disturbed. What points to stress having such a significant effect on IBS is that “people with IBS don’t typically have hypercontractility of their bowels when they are asleep.” (Sapolsky, ibid.) In other words, you aren’t stressed out while asleep, and as a result, you won’t be likely to have digestive issues at that time.

(Note: “Chronic stress worsens IBS symptomatology and [early life stressors] serves as a risk factor for IBS.” Also: “The amygdala has been found to consistently demonstrate altered activation to visceral stimulation in IBS patients. The amygdala is a brain nucleus that is important for the integration of the body’s neurophysiologic responses to stress, as well as modulating the perception of anxiety, which is increased in IBS. The amygdala … is a key brain nucleus involved in the facilitation of the stress response.” Beverley Greenwood-Van Meerveld and Anthony C Johnson. “Mechanisms of Stress-induced Visceral Pain,” in Journal of Neurogastroenterology and Motility. 2018; 24(1): 7-18.)


Vanner, Stephen et al. “Fundamentals of Neurogastroenterology: Basic Science.” Gastroenterology, S0016-5085(16)00184-0. 18 Feb. 2016. Please visit this website to read more: doi:10.1053/j.gastro.2016.02.018

Robert Sapolsky. Why Zebra’s Don’t Get Ulcers. New York, St. Martin’s Griffin, 2004: 82. Please visit Amazon.com to purchase this book.

The Society of Endocrinology’s website has a basic and straightforward explanation of cortisol and its roles in the body. Please visit their site for more information.

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