Malnutrition and cultural deprivation in infancy and early childhood tend to lead to retardation of psychomotor development, impaired learning and behaviour. Cerebral development being of an irreversible character, deprivation in the course of its evolution, especially during the immediate post-natal period, has irreversible consequences. Undernourishment in the mother can make the new-born baby's nervous system more fragile, and may lead to serious damage later on. Premature weaning can compromise the process whereby the neurones acquire myelin. The critical period of the brain's physical growth being between the fifth and the tenth month following birth, malnutrition at this time may reduce the number of cells in the brain, which has virtually finished growing by the end of the second year. Studies in Central Africa and Central America show that malnutrition during the first four years of life lead to mediocre intellectual performance when children reach school age. If there are other deficiencies in the environment, (psychological conditions, family situation, irregular school attendance) the child runs greater risk of suffering from other handicaps at school. Educational deficiency, the wrong kind of education or lack of education, even among children living in comfortable material conditions, may have disastrous consequences for cerebral development.