During the first years of life, an infant’s gut microbiota undergoes rapid colonization, and microbial diversity results from exposure to a variety of sources. These first years are also foundational for brain development, when neural networks growth and myelination occur rapidly and dynamically. A recent study in Biological Psychiatry explored how differences in gut microbial composition and diversity from fecal samples in 89 infants (1 year of age) impacted cognitive development and performance at 2 years of age.