Do We Have a Second Brain?

Have you ever heard of the enteric (or intrinsic) nervous system?

Well, the enteric nervous system is a major part of the autonomous nervous consisting of millions of neurons that have authority over the gastrointestinal system.

This system has the unique ability to localize blood flow, detect physiological and chemical conditions of the gut, and host reflex circuits controlling physical movements.

Since it is the only part of the nervous system ( apart from the CNS) that can work autonomously, it is often regarded as a “second brain”.

Burping in times of stress, a growling stomach in times of hunger and a squelching stomach in times of nervousness are just a few examples of the play of neurons with the digestive system. Additionally, the enteric nervous system also synthesizes its own dopamine, serotonin, and other hormones, which make it resemble the brain even more.

So, when we feel happy or excited, the serotonin and adrenaline work in coordination to constrict the blood vessels leading to our gut, thereby causing the “butterfly feeling”.

In fact, 90% of our body’s serotonin is present in our gut. It is synthesized in the enterochromaffin cells (a type of enteroendocrine/ neuroendocrine cell), which are located all over the epithelial layer of the gastrointestinal tract.

How are these hormones synthesized?

If the fact that 90% of our serotonin is synthesized in our gut seemed weird, the fact bacteria and microorganisms regulate its secretion may seem even more absurd.

In an experiment conducted by professors at Caltech, a group of mice were divided into 2 subgroups, out of which one was exposed to a particular type of bacteria. The group with bacteria produced 60% more serotonin than the other, and this percentage altered with factors such as duration and intensity of bacterial exposure.

As mentioned before, the serotonin is synthesized by the enterochromaffin cells and used as a neurotransmitter. With higher influx of the neurotransmitter, the mice exhibited higher chemical and electrical activity that ultimately stimulated the digestive tract.

A lot of research, time and effort is being put into finding advantages of the "second brain". Experiments are being carried out to use the hormones secreted by the ENS to treat people with depression, anxiety, and even neurological disorders such as Alzheimer's and Parkinson's disease.