The physical, chemical, and physiological development of the brain and consequent behavior in all species of higher animals evolves from the continuous interaction of genetic and numerous environmental factors. Among the latter are nutritional, disease, psychological, learning, and cultural variables. Of these, nutrition is concerned directly with providing energy and nutrients needed for cellular structures and various metabolic systems. Indirectly, food may serve as a stimulus for behavior as well as providing a basis for social interaction. In most instances, the specific effects of sub-optimal nutrition on brain development in man are inseparable from those of other environmental factors. In some instances--such as when nutrients are imperfectly utilized owing to inborn errors of metabolism, or when nutrients are lacking--malnutrition, per se, clearly alters the central nervous system by acutely or chronically limiting its metabolic, structural and functional capabilities and performance. In other circumstances, malnutrition, reflected in chronic limitation of amounts of food consumed, may result in general stunting of growth accompanied by reduced brain size, decreased brain cell number, and immature or incomplete biochemical organization of the brain. (Author/JM)