As Antonio Damasio highlighted back in 1994, Descartes' division of mind and body slowed the full realization of the connectedness of the brain and the body by centuries. The simple fact that homeostasis in the brain was fully interconnected with the body has eluded researchers and clinicians even after the connection was well established. Recent studies reporting the central role in dysfunction of mental systems as a result of inflammation in the gut and the autonomic nervous system (ANS) was yet one more reminder that the entire system is connected and interdependent. Central to this discovery and its application to mental function has been the growing field of study of the microbiome. This article is an attempt to situate those who are active in the variety of ways and means of treating the brain in the essential role that is likely being played by a vast community of bacteria living in the bowels of the human being and influencing all of the higher and most "sophisticated" aspects of human interchange and thought. It is the authors hope that this brief introduction will remind and inform researchers and clinicians that the organism is more interconnected and more complex than we have tended to think and that disorders of the mind are likely also, often disorders of the gut.
Keywords: brain health; gut-brain-axis; microbiome.