Sexual dimorphism of brain developmental trajectories during childhood and adolescence☆
Introduction
The degree to which sexual dimorphism extends to human brain anatomy has been the subject of many investigations, with most reporting total brain size to be ∼ 8–10% larger in males (Goldstein et al., 2001). However, the literature is notably inconsistent as to which subcomponents of the brain differ after accounting for the total brain size difference. Discrepant findings in sexual dimorphism studies may be partially accounted for by subject age, with some studies combining subjects across several decades. There is a particular paucity of data on sexual dimorphism of human brain anatomy between 4 and 22 years of age, a time of emerging sex differences in behavior and cognition (Cairns et al., 1985, Gouchie and Kimura, 1991, Johnson and Meade, 1987). Large individual variation in brain morphometry makes accurate characterization of developmental trajectories difficult with cross-sectional studies (Giedd et al., 1996c, Kraemer et al., 2000).
We compared trajectories of male and female brain development using longitudinal MRI data from healthy children and adolescents. Measures included gray and white volumes for the total cerebrum, frontal, temporal, parietal, and occipital lobes, volumes of the caudate nucleus and lateral ventricles, and corpus callosal area. Trajectories were compared by shape and by volume at the mean age.
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Subject selection
Subjects were healthy singleton or twin participants in an ongoing study at the Child Psychiatry Branch of the National Institute of Mental Health which began in 1989. Singleton subjects were recruited from the local community; twin subjects were recruited nationally. Only one subject from each family was included in the study; one member of each twin pair was chosen at random.
Healthy controls were screened via previously published criteria (Giedd et al., 1996a) which included an initial
Results
Robust sex differences in developmental trajectories were noted for nearly all structures with peak gray matter volumes generally occurring earlier for females. A representative scatterplot showing raw data for total brain volume and modeled developmental trajectories are presented in Fig. 1, Fig. 2, Fig. 3. A summary of relevant statistical analysis is presented in Table 3, Table 4.
Consistent with previous investigations (Giedd et al., 1999), mean total cerebral volume was approximately 10%
Discussion
Here we have demonstrated the importance of considering trajectories rather than group averages across broad age spans in investigations of brain sexual dimorphism. The finding that sex differences were age-dependent may partially account for discrepant findings of sexual dimorphism in the literature.
Previous work comparing brain growth patterns between males and females has been sparse and limited by small sample sizes or cross-sectional designs. In a cross-sectional sample of 118 healthy
Acknowledgments
RL and JG wrote the paper and oversaw data acquisition and analysis. JG conceived the study. NG was involved in acquiring and interpreting the data. AZ, JL, AE, JB, and CV were involved in analyzing the images. EM and GW were involved in subject recruitment and screening. DG and LC conducted the statistical analysis. PT was involved in image analysis and data interpretation.
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This research was supported [in part] by the Intramural Program of the NIH, NIMH.