The Role of the Brain–Gut–Microbiome in Mental Health and Mental Disorders

Better tools for studying the gut and microbiome have improved our understanding of the ways in which the gut microbiota affect brain function (through direct release of humoral messengers, through the actions on the gut and the enteric nervous system, and through the immune system). The microbiome is also affected by the brain, the immune system, and the enteric nervous system and the gut. One can consider the immune system, the brain, the enteric nervous system, and the microbiota as four control arms of behavior in a superorganism made up of both the animal cells and the microbial colony. Animal models and increasingly human studies suggest a role for the microbiome in several human diseases. Mood disorders, autism, and schizophrenia all have possible relationships with the microbiome. This chapter reviews some of the current examples of the complex interaction between microorganisms and animal host behavior and pathology.