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The real butterfly in your stomach: Scientists explore the possibility of a “second brain” in our gut

Ever had someone tell you to follow your gut? Or maybe you’ve been sitting with a test in front of you or a decision to make, and deep down there is something in your gut telling you what the correct answer or choice is.

Research has now revealed that what you may have thought of as an idiom —the “gut instinct”—passed down through the ages is actually deeply rooted in scientific fact.   For the past few decades, researchers have been studying the enteric nervous system—a part of the nervous system in the stomach. What they have found tells us not only a lot about what governs our bowel, but also about what controls instincts, mood and even some diseases.

The enteric nervous system (ENS) is a part of the peripheral nervous system, the nerves and ganglia (cell bodies) that lies outside of the brain.  It is defined as the “intrinsic innervations of the gut” explains Dr. Michael Gershon, Professor and Chairman of Anatomy and Cell Biology at Columbia University Medical Center and author of the 1998 book The Second Brain over email.

“I looked at the brain and found it daunting,” said Gershon in his email explaining why he chose to study this “second brain” over fifty years ago.  “I hoped to find an independent nervous system that was simpler to study than the brain.”

When Gershon started out, he was one of two researchers in the entire world looking into the ENS, noted a recent article in Psychology Today.  Now the study of the neurons and neurotransmitters that make up the ENS is the subject of the research of hundreds and the field of neurogasteroenterology is rising in popularity.




“There are between 200 and 600 million neurons in the human ENS, which is equal to the number of neurons in the spinal cord,” writes Dr. Emeran Mayer, the Director of the Center for Neurobiology of Stress at the David Geffen School of Medicine at UCLA, in a recent study published in Nature.

“[These neurons] regulate the behavior of the bowel and that of neighboring organs, including the gall bladder and pancreas,” says Gershon.

But the role of the ENS does not stop there.  The vagus nerves connect the ENS to the brain and when stimulated, these control epilepsy, relieve depression and improve learning and memory, Gershon further explains.

“[The implication of this is that] it is possible that signals from the bowel alter mood,” Gershon says.




If the neurons contained one of the major reasons that the ENS interests researchers is because it can operate without any input from the brain.

“The ENS is the only region of the PNS that is able to mediate reflexes and integrative neuronal activity in the absence of input from the brain or spinal cord,” says Gershon.

Another aspect of the ENS that has intrigued researchers is the reverse nature of the signaling between the brain and the ENS.  Traditionally, the brain is expected to signal the rest of the body. However, research has found that the ENS more commonly sends signals to the brain.

“Over 90% of the nerve fibers in the vagus nerves carry information from the guy to the brain.  This is shockingly more than the number of vagal fibers carrying information from brain to gut.”

As a result of these signals sent from the stomach to the brain, sadness, stress, memory, learning, and decision-making are affected, reports a recent article in Psychology Today.   This reverse signaling may explain why the idea of a “gut instinct” may actually be a scientific fact.




Recent research on the ENS has revealed many groundbreaking truths about the body.  For one, it has demonstrated that there may actually be a scientific link between food and feelings.

“Food and stress are powerful modulators of the body-mind connection,” reports a recent article published in the Journal of Clinical Investigation.

The ties between food and mood could offer promising treatments for the obesity epidemic, explain researchers Giovanni Cizza, M.D, Ph.D. and Kristina Rother, M.D, both from the National Institute of Health, in the article.

A group of researchers from the University of Leuven in Leuven, Belgium have studied the interactions between signaling initiated in the gut and the emotions that they elicit, according to a recent report published in the Journal of Clinical Investigation in August 2011.

They found that there was a relationship between the intake of fats and the level of neural activity in the brain as a result, reports the study.  They discovered that the intake of fatty acids reduced sadness and hunger.

“These findings increase our understanding of the interplay among emotions, hunger, food intake and meal-induced sensations in health, which may have important implications for a wide range of disorders, including obesity, eating disorders, and depression,” the researchers noted in their report.

Additionally, the ENS has also been thought to possibly have links to diseases such as autism.

“Autism has not yet been definitively linked to the ENS; however, it is likely that genetic defects in synapse formation which may contribute to autism affect development of the ENS as well as development of the central nervous system,” Gershon wrote in his email interview.




A study published in the journal Neurogastroenterology and Motility indicates that it is not simply the neurons and neurotransmitters in the stomach that play a role in signaling to the brain.  In fact, a large part of the work may be done by the “intestinal microbiota” in your gut—a.k.a. the germs in your stomach.

There are approximately 100 trillion bacteria that reside in your intestines, reports Psychology Today.  Researchers in Canada have studied these microbes and have concluded, “that the presence or absence of conventional intestinal microbiota influences the development of behavior and is accompanied by neurochemical changes in the brain.”

Some believe that this study could serve as a gateway to treating stress-related disorders such as depression, reports Psychology Today.




Neurogasteroenterology is now one of the cutting edge fields in the world of science.  Boston University students believe that it is important to explore new fields such as this one.

“Advancements such as these are important, because as the world changes, science needs to keep up with the advancements the human race is making in other areas.  It is especially important in medicine as new diseases are discovered every year, so new cures need to be found every year,” says Amanda Kirshkaln, a sophomore in the Sargeant College of Rehabilitation Sciences.

Students also agree that it is research into areas such as the ENS that are pushing the boundaries of science and medicine.

“These advancements are saving lives! I think they are important for a better understanding of the human body and to know our limits and go beyond!” says College of Arts and Sciences sophomore, Celia Gagliardi.

Research into the ENS has changed the way people are thinking about the relationship between the brain and the stomach. Much has changed since Gershon began his research 50 years ago.

“The idea that there are multiple neurotransmitters in the ENS is now accepted. The concept of the ENS as an independent region of the peripheral nervous system is also established,” Gershon notes. “The ENS is suspected to contribute to human GI disorders such as irritable bowel syndrome.  We know the ENS contains stem cells.”

When Gershon embarked on his study of the ENS, he thought he was choosing a simple system compared to the brain. However, Research has revealed that his initial hypothesis is far from the truth.

“My mistake was to think that the ENS could be described with the word simple,” Gershon admits in his email.  “A simple nervous system is an oxymoron.”

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  1. Excellent article summarizing the neuroscience findings on the enteric brain. Our behavioral modeling research on both the gut and heart brains shows they are involved in a number of core competencies including decision making, motivation, intuition and other important processes. Check out for details about how the multiple brains (head, heart and gut) communicate and how to align and harness their intelligence.

  2. on . February 25th, 2012 at . 3:15 am

  3. Hello,
    I would like to start off by saying how relieved I am to find that there is indeed a link between the human brain and the stomach more so than just the popular belief that the brain controls the entire human bodies functions. Now I have had thoughts that this was fact for a few years now not because of pure curiosity but because of personal expirience. I suppose I have a question that I feel could be answered more accurately by someone from this page rather than your typical physician. For years now I have had these headaches on the front left side of my head and seemingly every single time I would have a horrific stomach ache as well to go along with it. Now at first I just chalked it up to pure coincidence, but as time has progressed I have come to believe that my stomach and my brain are connected in more ways than many believe. Especially after finding this page it justifies my thoughts. My question is could there be something wrong in regards to the communication of my ENS and my brain? Maybe its even something as simple as something that is in my daily diet that needs to be addressed? I am no physician by any means but i have always been fascinated with the field of medicine and I love learning new things about the human body. If anyone has any insight on this topic I would appreciate a reply to the email listed above.

    Thank you,
    Derek Bloom