Brain Size and Cortical Structure in the Adult Human Brain

Abstract

We investigated the scale relationship between size and cortical structure of human brains in a large sample of magnetic resonance imaging data. Cortical structure was estimated with several measures (cortical volume, surface area, and thickness, sulcal depth, and absolute mean curvature in sulcal regions and sulcal walls) using three-dimensional surface-based methods in 148 normal subjects (n [men/women]: 83/65, age [mean +/- standard deviation]: 25.0 +/- 4.9 years). We found significantly larger scaling exponents than geometrically predicted for cortical surface area, absolute mean curvature in sulcal regions and in sulcal walls, and smaller ones for cortical volume and thickness. As brain size increases, the cortex thickens only slightly, but the degree of sulcal convolution increases dramatically, indicating that human cortices are not simply scaled versions of one another. Our results are consistent with previous hypotheses that greater local clustering of interneuronal connections would be required in a larger brain, and fiber tension between local cortical areas would induce cortical folds. We suggest that sex effects are explained by brain size effects in cortical structure at a macroscopic and lobar regional level, and that it is necessary to consider true relationships between cortical measures and brain size due to the limitations of linear stereotaxic normalization.

Deviant trajectories of cortical maturation in 22q11.2 deletion syndrome (22q11DS): A cross-sectional and longitudinal study

“…Indeed, volumetric studies have always reported reduced cortical volume in the syndrome (Eliez et al, 2000;Kates et al, 2004Kates et al, , 2001Simon et al, 2005;van Amelsvoort et al, 2001). If cortical volume is undeniably the product of its surface and thickness, surface changes are more susceptible to result in volumetric changes than thickness alterations (Im et al, 2008). Thus, the drastic cortical surface reduction that we observed in previous studies (Schaer et al, 2006 may better predict the decreased volume than subtle thickness changes associated with maturation.…”

Motion‐related artifacts in structural brain images revealed with independent estimates of in‐scanner head motion

“…A number of studies have suggested that head size (e.g., ICV) covaries with gray and white matter volume and cortical surface area, but generally not with GM thickness [Im et al, 2008; Pakkenberg and Gundersen, 1997]; accordingly, participant gender was used instead of ICV as a nuisance variable for statistical analyses of GM thickness [Barnes et al, 2010]. The results of this report remained qualitatively similar when using both covariates in statistical models.…”

Gender Differences in Cerebral Cortical Folding: Multivariate Complexity-Shape Analysis with Insights into Handling Brain-Volume Differences

“…It shows that handling ICV differences in folding studies may not be as simple as including ICV as a covariate in the underlying statistical test. This paper proposes two systematic methods for handling ICV changes in folding studies using the proposed descriptor and shows that while the findings using one method are consistent with [10], those using the other method are consistent with [11,12].…”

“…Moreover, while one study [10] using the fractal-dimension (FD) measure reported higher complexity in adult females, two very recent studies [11,12] using the isoperimetric ratio (IPR) measure report higher complexity in larger adult brains (i.e. males).…”

“…Convexity ratio (CR) [6] is the ratio of the area of the surface to the area of the convex hull/envelope of the surface. IPR [6,11,12] is the ratio of the surface area to the two-third power of the volume enclosed by the surface. Average curvedness (AC) [8] measures the deviation of the surface from a plane.…”