A wide range of recent animal studies have found a correlation between gastrointestinal pathology and psycho-neurological conditions such as depression, anxiety, autism spectrum disorder (ASD), schizophrenia, and neurodegenerative disorders.
Since 2013, the US National Institute of Mental Health (NIMH) has dedicated millions of dollars to fund seven different pilot studies that examine what scientists call the “Microbiome–Gut–Brain Axis.”
Animal studies continue to confirm that the brain responds to microbial signals from the gut. For example, scientists from McMaster University recently discovered that intestinal bacteria plays an important role in inducing both anxiety and depression. The July 2015 study, “Microbiota and Host Determinants of Behavioural Phenotype in Maternally Separated Mice,” was published in the journal Nature Communications.
Another 2015 study, “Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis,” led by Elaine Hsiao, a biologist now at UCLA, examined how certain metabolites from gut microbes promote serotonin production in the cells lining the colon. This finding is intriguing because SSRI antidepressants target serotonin reuptake at the junction between neurons. The serotonin producing cells in the digestive tract account for 60% of peripheral serotonin in mice and more than 90% in humans.
However, the exact communication methods between the human brain and our intestines remain enigmatic. We need more human studies on the “Gut-Brain Axis.” The exact correlation and causation between gut microbes and brain function is mysterious. That said, the growing body of evidence is fascinating and offers a new perspective on ways that we might improve our physical and psychological well-being.