The human cerebral cortex flattens during adolescence

Abstract

The human cerebral cortex appears to shrink during adolescence. To delineate the dynamic morphological changes involved in this process, 52 healthy male and female adolescents (11-17 years old) were neuroimaged twice using magnetic resonance imaging, approximately 2 years apart. Using a novel morphometric analysis procedure combining the FreeSurfer and BrainVisa image software suites, we quantified global and lobar change in cortical thickness, outer surface area, the gyrification index, the average Euclidean distance between opposing sides of the white matter surface (gyral white matter thickness), the convex ("exposed") part of the outer cortical surface (hull surface area), sulcal length, depth, and width. We found that the cortical surface flattens during adolescence. Flattening was strongest in the frontal and occipital cortices, in which significant sulcal widening and decreased sulcal depth co-occurred. Globally, sulcal widening was associated with cortical thinning and, for the frontal cortex, with loss of surface area. For the other cortical lobes, thinning was related to gyral white matter expansion. The overall flattening of the macrostructural three-dimensional architecture of the human cortex during adolescence thus involves changes in gray matter and effects of the maturation of white matter.

Figure 1.

Schematic representation of a gyrus and sulcus representing the different cortical morphometrics used in the current study.

Figure 2.

Parcellated hemispheric cortical surface overlaid with parcellated wire-frame representation of the cortical surface hull.

Figure 3.

Schematic representation of the image processing. FreeSurfer (version 5.1) and BrainVisa (version 4.2.1) software were combined.

Figure 4.

A, Pearson's partial correlations between percentages change over time relative to baseline of the cortical morphological measures. Only partial correlations that were significant (p < 0.05, two-tailed) after FDR correction (q = 0.05) are displayed. B–F, Scatter plots showing the relationship between different pairs of measures.