Tuesday 23 October 2018

Second Brain: why going with gut instinct is key to health

Fifteen to 20pc of us will suffer from Irritable Bowel Syndrome (IBS). Picture posed
Fifteen to 20pc of us will suffer from Irritable Bowel Syndrome (IBS). Picture posed

Patricia Casey

Very few people are aware that in our bodies lies a 'second brain'. While it doesn't engage in poetic thought or solve mathematical problems in the way that the brain in our skull does, nevertheless it is hugely affected by our emotional state and it, in turn, affects how we feel psychologically.

Do you ever have a gut instinct about a person? Perhaps your daughter's boyfriend to whom you have taken an instant dislike for some unfathomable reason, or your doctor whom you know at the first visit is trustworthy and likeable?

Then there are gut-wrenching experiences when you closely avoid a potentially serious collision or when you decided at the last minute not to take a train that crashed at high speed. Or the butterflies in your stomach before an exam or an interview that are well known to everybody.

The origin of these responses that involve the gut and stomach conveys the link between emotions and the gastrointestinal system.

Our bowels seem unlikely candidates to match our brain, but they possess some of the elements that have led to them being dubbed "the second brain".

The gut isn't just concerned with digesting and pushing food through, but has connections to various parts of the brain.

In fact, the control base for much of the activity of the bowel resides in the limbic system of the brain. This is the area that is, among other things, the seat of our emotional responses.

The vagus nerve also runs between the brain and the upper digestive system and stimulating this is now one of the newer treatments being investigated for those with severe depression.

Serotonin is a hormone in the brain that is partly linked to depressive illness and many antidepressants have been developed around this knowledge. But there are many more serotonin receptors in the gut than in the brain itself.

The bowel also contains a number of other neurochemicals found in the brain and linked to psychiatric disorders such as dopamine and noradrenaline. Enkephalins (natural painkillers) and natural benzodiazepine tranquilisers are also found in both the brain and the bowel. So at times of stress, when the fight-or-flight response is active and releasing chemicals such as noradrenaline into the brain, it is also stimulating the gut.

There are a number of conditions that are common in the general population. Irritable bowel syndrome (IBS) is one, another is called functional dyspepsia (continuous stomach ache), another is globus (formerly called globus hystericus) to denote difficulty swallowing. "Hystericus" suggested hysteria, something that was generated in the person's subconscious. Collectively they were called functional gastrointestinal disorders (FGIT).

Because no physical cause could be identified, doctors referred to them as functional, ie disorders of functioning. The sufferers unfortunately were invariably informed that these conditions were "all in the mind". Unsurprisingly this caused great distress and bewilderment to patients who knew and felt their symptoms to be real.

Research over the past decade shows that in this regard the doctor was not always right and that there was a plausible explanation for the symptoms. The mind-body interaction was real and the "how" of this was emerging.

While we can understand how the brain can affect the bowel (most of us will have had the physical experience of nervousness at some point in our lives), the reverse can also occur.

This is most clearly observed in certain types of cancer when the patient may present with psychological rather than physical symptoms in the first instance.

This is the case with some types of gastric and pancreatic cancers and both are associated with higher risks of depression and suicide than other types.

While suicide may be due, in part, to pain, a further possibility is that it is due to the reverse signalling between the neurochemicals common to bowel and brain.

Irritable bowel syndrome (IBS) is a condition that is present in about 10pc of the adult population in western Europe. It is also associated with a higher risk of depressive illness compared to those without it.

Environmental stress is one of the triggers and the loop of biological signals from brain to gut and back again perpetuate a cycle of physical and emotional symptoms.

While there are other hypotheses suggesting that micro-organisms in the stomach contribute, there is now clear evidence, from more than a dozen studies, that some patients with conditions such as IBS, derive benefit from psychological interventions which break the self-perpetuating loop between stress and symptoms.

Most of these studies had small sample sizes and more are required. Meanwhile, psychiatrist and colleague, Professor Ted Dinan at University College Cork, is at the forefront of the related area of the contribution of gut microbes to brain functioning.

For those who were thought to be "imagining" symptoms or who were dismissed as "hypochondriacs and whingers", this area of research will bring some comfort.

Research in this field may still be in its infancy, but it is raising many fascinating possibilities around our mind-body interaction.

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