The connection between the brain and the gut goes both ways. Psychobiotics in the gut can soothe your brain, but the brain can also affect your microbes. In a new study from the University of Nottingham, rats raised in isolation showed differences in their gut bacteria as well as changes in anxiety and brain development. The study suggests that life in solitary is no picnic. Early stress can produce lasting changes in gut microbes, leading to abnormal brain and immune function. This in turn can produce abnormal behavior and may play a key role in the development of psychiatric illness.