The Telegraph reports study finding that breastfed babies are more intelligent than bottlefed: "there were two schools of thought on how breastfeeding had an effect: that long-chain fatty acids in breast milk helped the brain develop; and that the act of breastfeeding improved the mother-child bond."
I would ascribe much of the benefit babies get from being breastfed to the fact that breast milk is low in sodium, lower in sodium than formula milk. And breast milk is, of course, the food that has evolved over millions of years as that best suited to human babies, especially newborns. Children, and babies in particular, are harmed by too high intake of sodium/salt. See Children and Salt Intake.