The Gut-Brain Connection

If you’ve ever felt “butterflies in your stomach” before a nerve racking event, or have experienced your stomach churn during intense periods of stress, you’re likely experiencing the resulting phenomenon of the gut-brain connection, or “the second brain.” Although the gut and brain are categorized into distinct body systems, their influences on each other are numerous. When examined, these connections hint at new avenues for mental health disorder treatments. So does good food really equal a good mood? Neuroscience surely suggests so. 

The Gut-Brain Axis

The Gut-Brain axis (GBA) refers to the collection of bidirectional communication mechanisms between the central and enteric nervous systems. Some components of the GBA are the enteric nervous system, vagus nerve, HPA axis, and neuroendocrine and neuroimmune systems. These direct links connect the emotional and cognitive sectors of the brain to peripheral intestinal functions. 

Enteric Nervous System

Composed of 100 million nerve cells lining the gastrointestinal tract, the enteric nervous system, or “little brain” doesn’t appear so little (Johns Hopkins Medicine). However, when compared to the 86 billion neurons of the brain, this title becomes more apparent (Voytek, 2013). The ENS is a component of the autonomic nervous system that is capable of controlling gastrointestinal activity without influence from the central nervous system (CNS). This gastrointestinal connection to the nervous system provides a possible explanation for diseases with effects on both the gastrointestinal and neurological systems, including Alezeihmers, Parkisons, and autism spectrum disorder (Rao and Gershon, 2016). 

For decades, anxiety and depression were believed to catalyze gastrointestinal issues, but the research of Dr. Jay Pasricha, M.D., director of the Johns Hopkins Center for Neurogastroenterology, proposes the contrary — ENS irritation contributes to anxiety and depression. Pasricha states his “… findings may explain why a higher-than-normal percentage of people with Irritable Bowel Syndrome (IBS) and functional bowel problems develop depression and anxiety,” In the healthy control population without IBS, anxiety is present in 8% of the population and depression 6%; Comparatively, the prevalence of anxiety is 5.5 times that of the healthy population, and depression 14 times, at 44% and 84% prevalence respectively (Banerjee, Arko, et al., 2017). The ENS’s connection to the Central Nervous System (CNS), provides a basis for gastrointestinal irritation, such as irritable bowel syndrome, to trigger mood changes. The implications of this research suggest a new pathway for gastrointestinal problem treatment, where antidepressants or psychological interventions traditionally used for mental health problems, could potentially improve illness in the gut. 

Vagus Nerve

The Vagus Nerve is the longest of the twelve cranial nerves, directly connecting the brain to the end of the colon. It’s somatic functions — sensation on the skin or in muscles — include providing the sensation of taste at the root of the tongue and feeling for the outer ear canal and skin behind the ear.  It’s visceral functions — sensation experienced by internal organs —  include most of the digestive tract, notably the larynx, tongue, and esophagus. Furthermore, the vagus nerve serves to stimulate muscles in the heart and aids in the lowering of the resting heart rate. 

Vagus Nerve Stimulation (VNS) through electrical-shocks has proved to be a potential treatment for those with treatment-resistant depression. A pulse regulator is placed in the chest, threaded underneath the skin to connect with the left vagus nerve, and periodically electrically stimulated. Approved by the FDA in 2005, doctors are still not entirely sure of why this therapy works, but it is suspected VNS helps to balance chemical disruptions in the brain (Taylor, 2019). Furthermore, VNS has proved effectiveness in the treatment of various neurological disorders, including Alzeihmer’s disease, multiple sclerosis, and cluster headaches. 


The gut produces a substantial amount of neurotransmitters, a group of signaling molecules released by neurons upon electrical cues for communication. More than 90% of monoamine serotonin receptors (5-HT), the neurotransmitter largely responsible for controlling happiness,  are produced in the gut (Yano, Jessica M, et al., 2015); The imbalance of serotonin has been cited as a potential cause of major depressive disorder. Furthermore, our gut microbes also produce a notable portion of gamma-aminobutyric acid (GABA), which is the neurotransmitter that regulates feelings of fear and anxiety (Robertson, 2020). 

Implications of the Gut-Brain Connection Research 

Investigation of the gut-brain connection is a relatively new concentration of study scientists are continuing to uncover. While our current understanding is limited, research suggests exciting potential treatment options; Treatments targeted at the brain could improve GI track issues, and treatments targeted at the GI track could treat mental health problems. 

TLDR? Remember to fuel yourself with good food, not just for your physical, but mental health as well. So go ahead — I mean, neuroscience says so — indulge in some of your favorite comfort food for your wellbeing. 🙂

Works Cited:

Banerjee, Arko, et al. “Anxiety and Depression in Irritable Bowel Syndrome.” Indian Journal of Psychological Medicine, Medknow Publications & Media Pvt Ltd, 2017,,that%20of%20depression%20was%206%25. 

“The Brain-Gut Connection.” Johns Hopkins Medicine, Johns Hopkins University, 

Rao, Meenakshi, and Michael D. Gershon. “The Bowel and beyond: the Enteric Nervous System in Neurological Disorders.” Nature News, Nature Publishing Group, 20 July 2016, 

Robertson, Ruairi. “The Gut-Brain Connection: How It Works and The Role of Nutrition.” Healthline, Healthline Media, 20 Aug. 2020, 

Taylor, Mara. “Vagus Nerve Stimulation for Depression.” Healthline, Healthline Media, 1 Apr. 2019, 

Voytek, Bradley. “Are There Really as Many Neurons in the Human Brain as Stars in the Milky Way?” Nature News, Nature Publishing Group, 20 May 2013, 

Yano, Jessica M, et al. “Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis.” Cell, U.S. National Library of Medicine, 9 Apr. 2015, 

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