Earlier brain imaging studies using prospective anatomic MRI scans measured gray and white matter changes that were summarized for individual lobes of the brain. While providing new insights, these lobar volume measures were limited by the lack of fine-scale details at sub-regional levels. These region-of-interest measures, for example, could not generally establish whether the functionally distinct sub-regions within a cortical lobe had structurally distinct developmental trajectories. They could not detect sweeping waves of dynamic changes that spread across the cortex, and were relatively insensitive to effects that did not coincide neatly with lobar boundaries. These limitations were overcome by more recent techniques that allow the measurement of cortical thickness or gray matter density at individual voxel locations in the image (e.g., voxel-based morphometry, VBM) (Ashburner et al., 2003) or across surface models of the entire cortex (Luders et al., 2005; P. M. Thompson et al., 2004; P. M. Thompson et al., 2005). Thus, ideally, using both global/lobar measures and GM density/thickness measures in a complimentary way can provide clearer understanding of brain development.
