Preclinical and a few clinical studies have demonstrated the existence of a brain-gut-microbiome axis in which bacterial signals can modulate affective behavior, brain activity, and central gene expression profiles. The study by Wang et al. in this issue (Wang H, Braun C, Murphy EF, et al. Bifidobacterium longum 1714™ strain modulates brain activity of healthy volunteers during social stress. Am J Gastroenterol 2019;114:1152-62.) contributes to a growing body of literature demonstrating that probiotics that alter behavior in animal models-termed "psychobiotics"-can induce changes in human brain networks involved in emotional or cognitive responses. Although there are still many unknowns about the potential of existing probiotics to induce clinically relevant effects, these findings support continued investigation into interventions acting on the brain-gut-microbiome axis for affective, cognitive, and behavioral disorders.