Psychobiotics: Shaping the Mind With Gut Bacteria

Introduction

There is a growing recognition—largely based on studies performed in laboratory animals—that the intestinal microbiomecan have wide-ranging effects on the brain. Germ-free mice (i.e., lacking all bacteria) have been found to have altered social, sensorimotor, exploratory, and stress response behaviors that are associated with neurophysiological abnormalities in diverse regions of the brain, including the prefrontal cortex, amygdala, hypothalamus, and hippocampus (1). Human microbiomestudies have also found associations of microbiome composition and function with neurobehavioral and affective disorders, as well as with brain neuroimaging parameters (2,3). The specific channels of communication between gut bacteria and the brain have begun to be elucidated. These include vagal nerve signaling, activation of enteric nerves, stimulation of enteroendocrine and enterochromaffin cells, release of neuroactive products into the circulation, and modulation of neuroimmune responses (4). This bidirectional interaction has been termed the brain-gutmicrobiome axis.