Gender effects on cortical thickness and the influence of scaling

Abstract

Using magnetic resonance imaging and well-validated computational cortical pattern matching methods in a large and well-matched sample of healthy subjects (n = 60), we analyzed the regional specificity of gender-related cortical thickness differences across the lateral and medial cortices at submillimeter resolution. To establish the influences of brain size correction on gender effects, comparisons were performed with and without applying affine transformations to scale each image volume to a template. We revealed significantly greater cortical thickness in women compared to men, after correcting for individual differences in brain size, while no significant regional thickness increases were observed in males. The pattern and direction of the results were similar without brain size correction, although effects were less pronounced and a small cortical region in the lateral temporal lobes showed greater thickness in males. Our gender-specific findings support a dimorphic organization in male and female brains that appears to involve the architecture of the cortical mantle and that manifests as increased thickness in female brains. This sexual dimorphism favoring women, even without correcting for brain size, may have functional significance and possibly account for gender-specific abilities and/or behavioral differences between sexes.

Figure 1

Summary of image preprocessing steps.

Figure 2

Average cortical thickness mapped for the whole sample (n = 60) in ICBM‐305 space after using 12‐parameter transformations (left) and after using 6‐parameter transformations (right). The brain surface is color‐coded according to the color bar, where thickness is shown in millimeters. Callosal, subcallosal, and midbrain regions have been excluded on the medial aspect of the surface.

Figure 3

Uncorrected statistical maps of gender differences in cortical thickness in ICBM‐305 space after using 12‐parameter transformations (left) and after using 6‐parameter transformations (right). The color bar encodes the P‐value associated with the t‐tests of cortical thickness performed at each cortical surface point. All colored cortical regions indicate statistically significant differences. All gray‐shaded regions are not significantly different between males and females.