ABSTRACT
Human brain growth follows a characteristic sigmoidal pattern (1). The short period of rapid growth is known as the brain growth spurt, which is the time when the brain is most vulnerable to noxious stimuli capable of impairing growth. There are also critical periods of physiological, biochemical, and psychological development when these variables are maturing at their most rapid rates. During each of these types of growth there are different types of growth ongoing, each with its own critical period. A good example is that anatomical growth encompasses a period when cell division is most rapid, which does not coincide with the period of most rapid myelination or with that of maximal dendritic arborization. The timing of each of these critical periods also differs from region to region in the brain. For instance, the activation of a given enzyme may occur later in the cerebellum than in the cerebrum. All of these critical phases of growth take place during intrauterine life or in the first 2 years of life. Once the chronological time has passed for a given type of growth, neither nutritional supplementation nor environmental or any other kind of stimulation can restart it. It is true that all facets of the growth process are time-dependent.
