Sex differences in cortical thickness mapped in 176 healthy individuals between 7 and 87 years of age - PubMed (original) (raw)

Sex differences in cortical thickness mapped in 176 healthy individuals between 7 and 87 years of age

Elizabeth R Sowell et al. Cereb Cortex. 2007 Jul.

Abstract

Findings from previous magnetic resonance imaging studies of sex differences in gray matter have been inconsistent, with some showing proportionally increased gray matter in women and some showing no differences between the sexes. Regional sex differences in gray matter thickness have not yet been mapped over the entire cortical surface in a large sample of subjects spanning the age range from early childhood to old age. We applied algorithms for cortical pattern matching and techniques for measuring cortical thickness to the structural magnetic resonance images of 176 healthy individuals between the ages of 7 and 87 years. We also mapped localized differences in brain size. Maps of sex differences in cortical thickness revealed thicker cortices in women in right inferior parietal and posterior temporal regions even without correcting for total brain volume. In these regions, the cortical mantle is up to 0.45 mm thicker, on average, in women than in men. Analysis of a subset of 18 female and 18 male subjects matched for age and brain volume confirmed the significance of thicker gray matter in temporal and parietal cortices in females, independent of brain size differences. Further analyses were conducted in the adult subjects where gender differences were evaluated using height as a covariate, and similar sex differences were observed even when body size differences between the sexes were controlled. Together, these results suggest that greater cortical thickness in posterior temporal inferior parietal regions in females relative to males are independent of differences in brain or body size. Age-by-sex interactions were not significant in the temporoparietal region, suggesting that sex differences in these regions are present from at least late childhood and then are maintained throughout life. Male brains were larger than female brains in all locations, though male enlargement was most prominent in the frontal and occipital poles, bilaterally. Given the large sample and the large range of ages studied, these results help to address controversies in the study of central nervous system sexual dimorphisms.

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Conflict of interest statement

Conflict of Interest: None declared.

Figures

Figure 1

(A) Maps of differences between the sexes in thickness of gray matter (males coded 1, females coded 0 for all maps displayed) for the entire group of 176 subjects showing differences in gray matter (in millimeters) between the male and female subjects according to the color bar on the right. Warmer colors (<0 on the color bar) are regions where gray matter thickness is greater in the female than in the male subjects, and cooler colors (>0) are regions where the males have greater gray matter thickness than the female subjects. Note the approximately 0.45 mm increase in cortical thickness in females in the right posterior temporal lobe. These maps are constructed without any brain scaling, so represent absolute thickness increases in women. (B) Maps of statistically significant differences in gray matter thickness between the sexes for the entire group of 176 subjects according to the color bar on the right (Pearson’s correlation coefficients ranging from −0.2 to 0.2 ranging from orange on the negative end to pink on the positive end). Regions in red correspond to correlation coefficients that show significant increase in gray matter thickness in the female subjects at a threshold of P = 0.05 and those in white correspond to significant increase in the male subjects at a threshold of P = 0.05.

Figure 2

(A) Gray matter thickness sex difference maps for the subgroup of 36 age- and brain volume–matched subjects showing differences in gray matter (in millimeters) between the male and female subjects according to the color bar on the right. Warmer colors (<0 on the color bar) are regions where females have thicker gray matter than the males, and cooler colors (<0) are regions where the males have thicker gray matter than the females. Note the approximately 0.6-mm thicker cortices in females in the right posterior temporal lobe. (B) Statistical differences between the sexes in gray matter thickness for the subgroup of 36 age- and brain volume–matched subjects showing the significance of gray matter thickness differences between the male and female subjects according to the color bar on the right (Pearson’s correlation coefficients ranging from −0.2 to 0.2). Regions overlaid in red correspond to correlation coefficients that show significant increase in gray matter thickness in the female subjects at a threshold of P = 0.05. There were no regions where the male subjects had thicker cortex than the females at a threshold of P = 0.05.

Figure 3

(A) Statistical P maps of the sex difference in cortical thickness in adults (aged >20 years) with height differences partialled out. The map is color coded according to the bar, and regions in red are statistically significant at a P value of 0.05 or less. Regions in pink and blue (i.e., on the dorsal and medial surfaces of the brain) do not approach significance with P values between 0.5 and 1.0. (B) Statistical P maps of the combined interaction terms age by sex and age2 by sex. The map is color coded according to the bar, and regions in red are statistically significant at a P value of 0.05 or less. Regions in pink (i.e., on the lateral surface of the right temporal and parietal lobes) do not approach significance with P values near 1.0.

Figure 4

Shown here is the same map as in Figure 1_A_ (right hemisphere) with scatterplots that show how gray matter thickness depends on age, in men and women separately, at various points over the brain surface situated approximately where the measurements were taken. On each of the y axes, cortical thickness is displayed in millimeters and age (7–87 years) is represented on the x axes. The axes are identical for all graphs. Male subjects are represented by blue points and the blue regression lines, and females are represented by the red points and the red regression lines.

Figure 5

DFC-H sex difference maps showing mean differences in DFC-H (in millimeters) between the male and female subjects according to the color bar on the right. Note the brain size increases up to 6 mm in the male subjects at the frontal and occipital poles bilaterally.

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Sex differences in cortical thickness mapped in 176 healthy individuals between 7 and 87 years of age - PubMed (original) (raw)