Fig. 3.

Gradients of cortical expansion are evident in an individual brain. Relative cortical expansion (local surface expansion normalized by total hemisphere expansion) is shown for each developmental period. For each column, the same map is overlaid on a younger (Top) and an older (Bottom) surface to visualize point correspondence after longitudinal registration. From Left to Right, relative expansion is estimated for growth from 27 wk to 31 wk PMA, 31 wk to 33 wk PMA, and 33 wk to 37 wk PMA. Far Right shows direct registration from 31 wk to 37 wk PMA, as considered for group analysis in Fig. 4. True cortical expansion is equal to relative expansion (plotted) multiplied by global cortical expansion of 1.26, 1.37, 1.70, or 2.33, respectively.