Can gut microbes play a role in mental disorders and their treatment?

The gut microbes, collectively called microbiota, are linked to the brain through a bidirectional system that involves the vagus nerve, the immune system, and various neurotransmitters. Stress response, memory functions, social behavior, and mood are modulated by microbiota. Furthermore, microbiota play a role in the development of the central nervous system. These features, established largely in rodent studies, have informed hypotheses about the role of microbiota in human psychiatric disorders. Microbiota affect phenomena that are known to be parts of the depression phenotype, such as exaggerated response to stress and inflammatory features. Furthermore, the role of microbiota in neurodevelopment and in the modulation of social behavior suggests the possibility of its role in autism spectrum disorder and in schizophrenia. If altered, microbiota play a role in psychiatric disorders, then efforts to normalize the gut microbial population by the ingestion of probiotics (live bacteria) could have antidepresssant or antipsychotic effects. Testing such hypotheses in translational human studies is a matter of future research.