Human milk contributes to higher intelligence and improved motor development later in life. At age 7½ to 8 years, even when adjusted for confounding factors such as parental education, socio-economic status, gender and the need for mechanical ventilation, children who had received human milk as premature babies scored an average 8.3 points higher on IQ tests than children who had been fed formula. (Lucas 1992) In another study, of full term babies, long term intelligence and improved motor development directly correlated with duration of breastfeeding.
(Lucas, A et al. Breastmilk and subsequent intelligence quotient in children born preterm. Lancet 1992; 339:261-64.
Rogan, W. and Gladen, B. Breastfeeding and cognitive development. Early Human Dev 1993; 31:181-93.)