investigators suggested that continued intra-cortical myelination might also partly explain the progressive reduction in the amount of tissue with a gray matter appearance on MRI (T. Paus, 2005). The developmental trajectories for each lobe were also surprising, because for the first time they showed that GM development was heterogeneous across the major lobes; frontal lobes had peak GM volumes around age 11, while the temporal lobes continued to increase in volume until 14 years, and the cerebellum showed the most protracted developmental time-course. On the other hand, white matter volumes increased roughly linearly throughout the first four decades of life, with a peak around the mid-forties when speed for certain fine motor skills is also optimal (Bartzokis et al., 2008).
