Human brain development involves a cascade of processes that starts two weeks post conception, when the first cell differentiates. These processes interact with each other and have different dynamics and termination times: some are completed at birth, whereas others continue to develop throughout the lifespan (Figure 1). By 3–4 weeks of gestation, the neural tube is formed, which then differentiates into the full nervous system between 4 to 12 weeks. Cells proliferate and give rise to neurons. From 12 to 20 weeks, these neurons migrate along the radial cells to their final destination and form the cortex (Rakic 1990). Between 24 weeks into gestation to 4 weeks after birth, the first apoptosis occurs, reducing the number of neurons by half. Concurrently, myelination begins at 29 weeks of gestation in the brain stem and develops primarily from inferior to superior and from posterior to anterior directions (Volpe, 2000; Huppi et al, 2001). By early childhood, most of the axons are myelinated, although myelination continues through adolescence and across the second and third decades of life (Yakovlev 1967; Benes et al. 1994;
