Modulating microbiota can modulate the mind.

Much research has been done to explore the connection of the gut and the brain, particularly of the HPA axis. For years, the hypothesis of how the gut microbiota could influence the brain has been a question of much debate. Researchers have attempted to examine how psychiatric conditions were improved by altering the microflora of the GI system. Modifications of the gut were made through the administration of probiotics and found that this minimized anxiety in animal studies and decreased serum cortisol in patients.
Evidence has shown that prenatal and postnatal periods are a time of rapid development of the brain and is susceptible to influences inutero. Epidemiological data found that there was an association of neurodevelopmental disorders and exposure of pathogenic microbes.
It has been suggested that as carbohydrates found in the diet are broken down to become short chain fatty acids this induces colonic motility, suppresses incidence of colon cancer, and helps to regulate the appetite. Short chain fatty acids also interact with the sympathetic nervous system via nerve cells and aid in memory and learning processes. Bifidobacteria infantis, a bacterium found in the gut, has been shown to increase the presence of tryptophan, thus influencing the pool of serotonin. This could then influence behavior. Lactobacillus rhammosus has demonstrated efficacy in lowering stress induced levels of corticosterone, anxiety and depression related behavior found in animal studies.
T-regulatory cells found in the gut also play an active role in immune function. GALT is influenced by differing microbes, pathogens, and interleukins. Interleukin 17 is converted to TH17 cells and crosses the blood-brain barrier. Thus, altering the gut-brain axis, immune function, and behavior.
The gut microbiome has a profound effect on neurotransmitters, GALT, and the endocrine system. Researchers have accomplished much in the field of discovery of how the microbiome of the gut influences the brain, however, much research still needs to be explored.