Why do we go with our gut?
Have you ever felt butterflies in your stomach? Had a gut feeling about a person? Or felt a lump in your throat, while watching a gut-wrenching movie?
We use these expressions on a daily basis, but proof that our guts affect our emotions has only surfaced in the last few decades. In fact, the gut is called our second brain.
The brain and spinal cord control our organs through nerves running throughout the body, like tree roots spread wide to the tips of our fingers and toes. But our digestive tract is so complex that it has an entire nervous system dedicated to it, called the enteric nervous system (or ENS).
What’s our second brain made of? How does it work?
Like the brain, the ENS is mostly made of nerve tissue. This is pretty cool given that our other organs are mostly muscle tissue! The ENS and brain mainly talk to each other via a highway called the vagus nerve. While other organs need to be coordinated by the brain, scientists have found that cutting the vagus nerve doesn’t affect digestive tract function. It simply keeps moving food along, producing hormones and enzymes, and churning food. Our gut can survive on its own — kind of like how a cockroach can still crawl when it’s been decapitated. (Sorry for the visual!)
This doesn’t mean that our brain and ENS don’t communicate much. It’s just that most of the information — around 80% — flows towards the brain, not the other way round. For example, think about when you’re choked up after a touching birthday wish; the nerves in your throat are highly stimulated so you have trouble swallowing. Being afraid means chemicals in the brain are released, simultaneously making you “sh*t your pants”.
From an evolutionary perspective, this strong connection between our digestive tract and brain makes sense. Our ancestor’s survival constantly depended on what they could eat.
Hmm, is this poisonous? Will I get enough energy from it to survive the day? Credit: Flickr (Aleksey Gnilenkov)
What’s the connection between our two brains?
Your brain makes chemicals called neurotransmitters that send signals between the 100 billion neurons within it, like telephone cables that network throughout a city; but the same chemicals are also made in the gut. In fact, 90% of our body’s serotonin – a chemical that regulates mood and digestion – resides in our gut. This is why antidepressants can actually ease the symptoms of Irritable Bowel Syndrome!
Dopamine, a reward-associating neurotransmitter, is also found in the gut. It was mind-blowing when scientists found out Parkinson’s patients often encounter digestive problems up to ten years before their diagnosis. This discovery has shed a whole new light on Parkinson’s, an uncurable mental disorder caused by a lack of dopamine.
Along this line of evidence, it’s no wonder that drugs like morphine and heroin— that are meant to affect the brain — create side effects including constipation, cramps, and nausea.
This is an exciting time for both pharmacology and psychology, which are intricately related to one another. New drugs can be developed for both mental disorders and gut disorders without adverse side effects, which affect a whopping 2 million people in the USA each year. In fact, an entire branch of research called neurogastroenterology is now dedicated to the relationship between our two brains!
So in a nutshell, our gut can be independent from the brain, but they still communicate constantly — much like a healthy relationship. Understanding the connection between the gut and the brain has huge implications, more than ever before, especially on designing more effective drugs without side effects.