Gacias et al. divided NOD mice into four groups, with each group receiving a different treatment (top). Only mice that received the oral control showed a change in behavior. These mice were less social and showed more "despair-like behaviors". These mice also had reduced myelination in the medial prefrontal cortex (this region’s location in the brain is shown with a blue dot). The gut microbiomes in these mice also became enriched with bacteria called Bacteroidetes and Firmicutes. Oral antibiotics didn’t affect behavior, but did reduce the diversity of the gut microbiome. Injections (control or antibiotics, right) had no effects.