The brain, the gut, and the gut’s internal microbiota all communicate as a part of the gut-brain-microbiota axis. Neurotransmitters from the brain and nervous system are sent down to the gut where the gut and bacteria receive and respond to the signal. Conversely, Bacteria in the gut can release signals that are then picked up by the nervous system and then sent to the brain (1). In such instances as depression, negative mental valance is directly associated with microbial dysbiosis in the gut, possibly due to communication between the brain and the gut microbial communities (2). Looking at it the other way around, people with dysbiotic guts (i.e., those with IBS) have a higher risk of suffering from a mental illness (3). In this way, the problem becomes like that of the chicken and the egg; which one comes first? It is undeniable that the brain can communicate with microbial communities in the gut, but that doesn’t necessarily mean the opposite is untrue.

Works Cited

1: Martin CR, Osadchiy V, Kalani A, Mayer EA. 2018. The Brain-Gut-Microbiome Axis. Cell Mol Gastroenterol Hepatol 6:133–148.

2: Madison A, Kiecolt-Glaser JK. 2019. Stress, depression, diet, and the gut microbiota: human–bacteria interactions at the core of psychoneuroimmunology and nutrition. Curr Opin Behav Sci 28:105–110.