The idea that bacteria teeming in the gut—collectively known as the microbiome—can affect not only the gut, but also the mind, "has just catapulted onto the scene," says neuroimmunologist John Bienenstock, MD, of McMaster University in Hamilton, Ontario. In just the last few years, evidence has mounted from studies in rodents that the gut microbiome can influence neural development, brain chemistry and a wide range of behavioral phenomena, including emotional behavior, pain perception and how the stress system responds.
Research has found, for example, that tweaking the balance between beneficial and disease-causing bacteria in an animal's gut can alter its brain chemistry and lead it to become either more bold or more anxious. The brain can also exert a powerful influence on gut bacteria; as many studies have shown, even mild stress can tip the microbial balance in the gut, making the host more vulnerable to infectious disease and triggering a cascade of molecular reactions that feed back to the central nervous system.
Such findings offer the tantalizing possibility of using beneficial, or probiotic, bacteria to treat mood and anxiety disorders—either by administering beneficial microbes themselves or by developing drugs that mimic their metabolic functions. The new research also hints at new ways of managing chronic gastrointestinal (GI) disorders that are commonly accompanied by anxiety and depression, and that also appear to involve abnormal gut microbiota.
