Abstract
The corpus callosum (CC) is the largest connective pathway in the human brain, linking cerebral hemispheres. There is longstanding debate in the scientific literature whether sex differences are evident in this structure, with many studies indicating the structure is larger in females. However, there are few data pertaining to this issue in infancy, during which time the most rapid developmental changes to the CC occur. In this study, we examined longitudinal brain imaging data collected from 104 infants at ages 6, 12, and 24 months. We identified sex differences in brain-size adjusted CC area and thickness characterized by a steeper rate of growth in males versus females from ages 6–24 months. In contrast to studies of older children and adults, CC size was larger for male compared to female infants. Based on diffusion tensor imaging data, we found that CC thickness is significantly associated with underlying microstructural organization. However, we observed no sex differences in the association between microstructure and thickness, suggesting that the role of factors such as axon density and/or myelination in determining CC size is generally equivalent between sexes. Finally, we found that CC length was negatively associated with nonverbal ability among females.
Highlights
The corpus callosum (CC) is the primary anatomical connection between brain hemispheres, consisting of several hundred million fibers (Tomasch, 1954)
Learning Composite standard scores from the Mullen Scales of Early Learning (MSEL) at age 24 months were higher for females (M 1⁄4 116.1, SD 1⁄4 14.9) than males (M 1⁄4 108.1, SD 1⁄4 13.9), t(102) 1⁄4 2.8, p 1⁄4 0.006, g 1⁄4 0.55
Our results indicate that male and female infants appeared relatively equivalent in terms of CC size at age 6 months, with differences emerging from late infancy through toddlerhood
Summary
The corpus callosum (CC) is the primary anatomical connection between brain hemispheres, consisting of several hundred million fibers (Tomasch, 1954). The structure is unique to eutherian mammals (Mihrshahi, 2006) and has been studied in detail in human and nonhuman primates (Hofer et al, 2008; Sakai et al, 2017a). The most dramatic changes to this structure occur during the first years of life, followed by a period of growth that extends through childhood before plateauing post-adolescence (Rauch and Jinkins, 1994; Luders et al, 2010; Tanaka-Arakawa et al, 2015). While the majority of existing work has been based on cross-sectional data, there are longitudinal studies substantiating that CC growth rates vary by region and follow a rostral-caudal progression during later childhood (Giedd et al, 1999; Thompson et al, 2000; Westerhausen et al, 2016).
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