Recent years have witnessed an increased attention to studies of sex differences, partly because such differences offer important considerations for personalized medicine. While the presence of sex differences in human behaviour is well documented, our knowledge of their anatomical foundations in the brain is still relatively limited. As a natural gateway to fathom the human mind and behaviour, studies concentrating on the human brain network constitute an important segment of the research effort to investigate sex differences. Using a large sample of healthy young individuals, each assessed with diffusion MRI and a computerized neurocognitive battery, we conducted a comprehensive set of experiments examining sex-related differences in the meso-scale structures of the human connectome and elucidated how these differences may relate to sex differences at the level of behaviour. Our results suggest that behavioural sex differences, which indicate complementarity of males and females, are accompanied by related differences in brain structure across development. When using subnetworks that are defined over functional and behavioural domains, we observed increased structural connectivity related to the motor, sensory and executive function subnetworks in males. In females, subnetworks associated with social motivation, attention and memory tasks had higher connectivity. Males showed higher modularity compared to females, with females having higher inter-modular connectivity. Applying multivariate analysis, we showed an increasing separation between males and females in the course of development, not only in behavioural patterns but also in brain structure. We also showed that these behavioural and structural patterns correlate with each other, establishing a reliable link between brain and behaviour.
Check also Multifaceted origins of sex differences in the brain. Margaret M. McCarthy. Phil. Trans. R. Soc. B Vol. 371, Issue 1688, February 19 2016. https://doi.org/10.1098/rstb.2015.0106
Abstract: Studies of sex differences in the brain range from reductionistic cell and molecular analyses in animal models to functional imaging in awake human subjects, with many other levels in between. Interpretations and conclusions about the importance of particular differences often vary with differing levels of analyses and can lead to discord and dissent. In the past two decades, the range of neurobiological, psychological and psychiatric endpoints found to differ between males and females has expanded beyond reproduction into every aspect of the healthy and diseased brain, and thereby demands our attention. A greater understanding of all aspects of neural functioning will only be achieved by incorporating sex as a biological variable. The goal of this review is to highlight the current state of the art of the discipline of sex differences research with an emphasis on the brain and to contextualize the articles appearing in the accompanying special issue.
But there is another window into the human brain and that is through the minds of boys and girls. Hines has discovered a robust sex difference in toy preference between boys and girls and has convincingly demonstrated over many studies that girls prenatally exposed to androgen owing to a genetic anomaly (congenital adrenal hyperplasia (CAH) girls) have a boy-like toy preference [30,31]. In this issue, Hines [32] makes another major leap forward in illuminating how androgens impact the developing human brain with evidence that CAH girls are less sensitive than unaffected girls to extraneous socialization cues about gender-appropriate toy-choices. Thus, rather than concluding that there is some undiscovered ‘prefers-dolls-nucleus' in the brain, her recent work demonstrates how children are differentially sensitive to socializing cues, so that girls become even more girl-like by modelling the behaviour of other females. In this way, the nature versus nurture conundrum is broken down with the realization that nature determines the response to nurture. Whether the converse is true for boys is not yet known.
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