Structural MRI measurements of white matter (Giedd et al. 1999), diffusion tensor imaging (DTI, Snook et al. 2005) and post-mortem myelin staining (Yakovlev and Lecours 1967) have demonstrated increased cortical myelination in the age ranges found in the studies described in this review. However, despite these demonstrable changes, a note of caution is needed regarding directly linking processes such as myelination and synaptic pruning to the phenomenology observed in the development of the brain's functional architecture. One should avoid assuming that there is an isomorphic relationship between myelination and integration on the one hand, and pruning and segregation on the other.
