Structural asymmetry of the human cerebral cortex: Regional and between-subject variability of surface area, cortical thickness, and local gyrification

Abstract

Structural asymmetry varies across individuals, brain regions, and metrics of cortical organization. The current study investigated regional differences in asymmetry of cortical surface area, thickness, and local gyrification, and the extent of between-subject variability in these metrics, in a sample of healthy young adults (N=200). Between-subject variability in cortical structure may provide a means to assess the extent of biological flexibility or constraint of brain regions, and we explored the potential influence of this variability on the phenotypic expression of structural asymmetry. The findings demonstrate that structural asymmetries are nearly ubiquitous across the cortex, with differing regional organization for the three cortical metrics. This implies that there are multiple, only partially overlapping, maps of structural asymmetry. The results further indicate that the degree of asymmetry of a brain region can be predicted by the extent of the region's between-subject variability. These findings provide evidence that reduced biological constraint promotes the expression of strong structural asymmetry.

Keywords: Cortical parcellation; Cortical thickness; Cortical variability; Local gyrification; Structural asymmetry; Surface area.

Figure 1

Statistical map of univariate t-values testing the significance of regional asymmetries. Positive values (warm colors) indicate leftward asymmetry, negative values (cool colors) indicate rightward asymmetries. Areas with nonsignificant asymmetries are shown in purple. Regions not examined due to low concordance indices (Destrieux et al., 2010) are indicated in gray.

Figure 2

Correlation of asymmetries across each cortical metric (only FDR-corrected statistically significant correlations are shown). A. Surface area X local gyrification asymmetry correlation. B. Surface area X Thickness asymmetry correlation. C. Thickness by local gyrification asymmetry correlation.

Figure 3

Regional coefficient of variation for the right hemisphere. Cool colors indicate coefficients below the median value; warm colors indicate coefficients above the median value. Regions not examined due to low concordance indices (Destrieux et al., 2010) are indicated in gray.

Figure 4

Regional coefficient of variation for the left hemisphere. Cool colors indicate coefficients below the median value; warm colors indicate coefficients above the median value. Regions not examined due to low concordance indices (Destrieux et al., 2010) are indicated in gray.

Figure 5

Scatterplots of the correlations between the absolute value of asymmetry and the coefficient of variation. Each correlation coefficient was computed over the 68 regional parcellations.