Folate and the B vitamins are essential for brain development, but we actually know very little about why or how. Dr. Aron Troen starts with the B vitamins, reviewing the indirect evidence supporting their role in cognitive function, including genetic, animal, and clinical studies. Troen then goes through the handful of clinical studies relating Vitamin B status to cognitive development in children, showing the relationship between folate and Vitamin B status in several health outcomes. High folate and low B12 levels increase the risk of cognitive impairment, insulin resistance and lower hemoglobin status. Next, Troen considers the role of folate. Although the importance of folate in preventing neural tube defects is well-established, there is little information on the biological effects of folate. In examining the effects of folate on parameters such as NK cell activity, telomere length and spinal sensory neuron regulation, Troen reveals the bell-shaped dose-response to folate, where high and low levels have detrimental effects. He ends his talk with neuroepigenetics, showing how maternal diet can affect brain development of the infant via the mechanisms of DNA methylation.