A groundbreaking study has uncovered a critical brain-gut connection that links psychological states to changes in the gut microbiome, with profound implications for immune function and stress-related health conditions. The research, now published in the journal Cell, reveals how stress-sensitive brain circuits influence the composition of gut bacteria through Brunner’s glands in the small intestine. It sheds light on the intricate mechanisms by which mental states can impact physical health, pointing to new possibilities for therapeutic intervention, for example against inflammatory bowel disease.