The Microbiome-Gut-Brain Axis Relies on Your Vagus Nerve

There is growing evidence that the trillions of microbes inhabiting our gastrointestinal tracts (commonly referred to as microbiome or gut microbiota) play a mysterious yet significant role in many aspects of our mental health—ranging from psychological resilience to neuropsychiatric disorders.

Researchers from the Department of Psychiatry and Psychotherapy at the University of Regensburg in Germany recently conducted an international review of microbiome-gut-brain (MGB) clinical studies. Their paper, “'I Am I and My Bacterial Circumstances': Linking Gut Microbiome, Neurodevelopment, and Depression,” was published online ahead of print August 22 in the journal Frontiers in Psychiatry. (The title of this review refers to an Ortega y Gasset maxim: “I am I and my circumstance; and, if I do not save it, I do not save myself.”)

The authors of this review are optimistic that gaining a better understanding of gut microbiota and the microbiome-gut-brain axis will help psychiatrists and psychotherapists create radical new ways to treat mental health issues more effectively in the near future.

The microbiome-gut-brain (MGB) axis is a bidirectional feedback loop facilitated in part by the vagus nerve which sends communication "down" from brain-to-gut and "up" from gut-to-brain using efferent and afferent nerve fibers.

Source: chombosan/Shutterstock

Juan Lima-Ojeda, lead author of the 'I Am I' paper, summed up his team's research question in a statement: "The main idea of our review is that there is strong communication between the GI tract and the brain and that changes to the microbiome-gut-brain axis could be associated with the etiology of different neuropsychiatric disorders such as depression.” For their review, Lima-Ojeda and colleagues analyzed a large body of clinical studies that had investigated the role of gut microbiome on mental health with a particular focus on the “microbiome-gut-brain axis” which refers to the bidirectional communication between the brain, gut, and microbiome.

The gut-brain axis is a complex network that integrates microbiome colonies with the nervous system and brain. In a description of how this feedback loop works, the authors write: “The gut microbiome influences the function of the brain by modulation of both immune and endocrine systems, HPA axis, neurotransmitter pathways, and growth factors. Alterations of this network—that includes numerous molecules and cells—may be the basis of pathological processes.”

The Microbiome–Gut–Brain Axis: Gut Microbiome and Your Vagus Nerve

Vagus means "wandering" in Latin. The vagus nerve is known as the "wandering nerve" because it has multiple branches that diverge from two thick stems rooted in the brainstem that wander to the lowest viscera of your abdomen touching your heart, lungs, and most major organs along the way.

Source: Wellcome Library/Public Domain

Notably, the vagus nerve—which is the longest nerve in the human body and wanders from the brainstem to the lowest viscera of your intestines—is like a communication superhighway of connectivity between your gut and brain. In their latest review, Lima-Ojeda et al. describe how the vagus functions: “A main characteristic of this system is its bidirectionality, where a neuro-endocrino-immunological connection is implicated. In general, the gut-brain axis is important regulating gastric and intestinal function and energy homeostasis. The tenth cranial nerve or vagus nerve, with its both afferent and efferent fibers, is a link between the gastrointestinal tract and the brain."

In the conclusion of this microbiome-gut-brain axis review, the authors state: “The evidence presented above suggests that the link between the MGB axis, the neuroendocrine–immune system—including energy homeostasis mechanisms—and the neurodevelopment is strong. Human neurodevelopment is a dynamic and long process that begins very early, during the intrauterine life, and continues during years, into the adulthood. These characteristics of the nervous system’s development—both its chronicity and dynamisms—make this process susceptible for alterations. Moreover, the origin of the gut-brain axis takes place early during the prenatal period, directly after the beginning of the neurodevelopment. The gut-brain bidirectional connection is present early in development, playing this network a key role modulating the formation of the brain.”

Specific Strains of Gut Microbiome Are Linked to Peak Athletic Performance

Pioneering discoveries about various microbiome strains and the gut-brain axis are being published and presented at breakneck speed. For example, on August 20, researchers from Harvard Medical School (HMS) presented state-of-the-art findings that link specific gut microbiome with peak athletic performance at the 254th National Meeting & Exposition of the American Chemical Society (Aug. 20-24, 2017) in Washington, DC.

This ongoing sports-related microbiome research is being led by Jonathan Scheiman, a postdoctoral candidate in the Department of Genetics at HMS, and professor George Church of Harvard and the Massachusetts Institute of Technology (MIT). To read more about their presentation, check out my Psychology Today blog post, “Does Gut Microbiome Influence Mindset and Mental Toughness?”

For the past two years, Scheiman et al. have been sequencing the microbiome of elite athletes using computational metagenomic methods to identify and isolate novel probiotic bacteria among Boston marathon runners, Olympic rowers, and ultra-endurance athletes who run 100+ miles at a stretch. Their ultimate goal is to develop probiotic supplements to improve physical and psychological athletic performance while aiding speedier recovery for both weekend warriors and elite competitors.

In March 2017, Terrence McNally interviewed Scheiman and Church for a “Disruptive” podcast, produced by Harvard's Wyss Institute for Biologically Inspired Engineering. During this interview, Scheiman speculated about the role that microbiome might play in the convergence of athletic mindset and mental toughness through the lens of sports genomics and the gut-brain axis. Scheiman said:

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“Certainly, if you look at gut-brain axis and the notion of mental toughness applications among professional athletes and elite athletes. If you look at the pressure that they face on a daily basis with competition, I would reason that perhaps they have some bugs in their gut that could help them stay calm during these times of high anxiety. Certainly, they could benefit from bugs that may be able to calm them and help them with mental toughness. There have been studies which spoke about gut-brain axis and mental toughness, and how they influence calmness and anxiety levels in people.”

On a psychological well-being scale of -5 to +5, gaining a better understanding of the vagus nerve and microbiome-gut-brain axis function could help people from all walks of life stay in positive territory. (If you'd like to learn some practical ways to engage your vagus nerve and stay calm, cool, and collected during times of distress check out my nine-part Vagus Nerve Survival Guide series.)

Hopefully, ongoing research on gut microbiome and the vagus nerve will lead to novel ways for mental health professionals to help patients who are 'south of zero' improve clinical outcomes. From a positive psychology perspective, identifying specific strains of microbiota linked to peak performance, endurance, and recovery could result in probiotics or nutraceuticals that catapult people 'north of zero.' The microbiome-gut-brain axis also has the potential to fortify mental toughness in both sport and life.