"There can be no brain without a body to inhabit, and no body could survive without a brain inside it. The body is a single organism that includes the specialist functions of the brain, which include those of taking account of what is happening in the body, including the part of it that is itself." Antonio Damasio, author of 'Descartes' Error' and 'The Feeling of What Happens'.
As a practitioner and student of Mindfulness, I am interested in mind and body, which might perhaps more accurately by thought of as bodymind. I was recently discussing this in some depth with colleagues who are similarly interested in aspects of neuroscience as they pertain to our health and wellbeing.
"What the mind dwells upon the body acts upon"
Dennis Waitley, American inspirational speaker and self-help author, b.1933
Given the very basic level of my biological knowledge, our discussion of the vagus nerve stood out as something of importance to me. Our capacity to self soothe is nothing less than crucial to our survival. The vagus nerve would seem to be critical in the management and expression of our emotions. Darwin highlighted this, in 1872 but did not have the same science at his disposal as we do today. It has since been shown that the vagus nerve plays a critical role in affect management through the regulation of brain structures, and is related to epilepsy, depression and repetitive self destructive habits such as those found in autism. Activation of the vagus nerve typically leads to a reduction in heart rate, blood pressure, or both. Within the healthy range of activation, it is the vagus nerve that allows us to comfort and soothe ourselves, and interact with other people.
Similarly, our digestive system is at the heart of the network with which we process our emotional experience. This confirms the existence of 'gut feelings' - we really do process our feelings in our intestine. There are said to be 100 million neural networks lining intestinal walls which comprise our enteric nervous system - we do, quite literally, have a second brain in the gut.
"The second brain doesn't help with the great thought processes…religion, philosophy and poetry is left to the brain in the head."
Michael Gershon (1999) 'The Second Brain', Harper Collins.
Butterflies in the stomach - signaling in the gut as part of our physiological stress response, is but one example. Although gastrointestinal turmoil can sour one's moods, everyday emotional well-being may rely on messages from the brain below to the brain above.
Given the two brains' commonalities, other depression treatments that target the mind can unintentionally impact the gut. The enteric nervous system uses more than 30 neurotransmitters, just like the brain, and in fact 95 percent of the body's serotonin is found in the bowels. Because antidepressant medications called selective serotonin reuptake inhibitors (SSRIs) increase serotonin levels, it's little wonder that meds meant to cause chemical changes in the mind often provoke GI issues as a side effect. Irritable bowel syndrome (IBS) which afflicts between 20-25% population at some time in their lives, also arises in part from too much serotonin in our entrails, and could perhaps be regarded as a "mental illness" of the second brain.