Sex Differences in Brain Function

Abstract

Sex differences in the brain come in many sizes, shapes and forms. The most robust differences between males and females are not surprisingly those directly relevant to reproduction. The neural underpinnings controlling sex behaviour and control of gonadal function are establishing during a developmental sensitive period by the differential hormonal milieu found in males versus females. Considerable advances have been made in identifying the cellular mechanisms of early organizational effects of testosterone and its metabolite estradiol, which then determine adult physiology and behaviour. These mechanisms are highly region‐specific and impact on cell death, axonal projections and synaptogenesis, resulting in a brain that combines varying degrees of maleness and femaleness. The study of reproductive endpoints is not only valid in its own right but also provides insight into the more subtle sex differences associated with cognition, emotionality, social behaviour and relative risk of neurological disorders and diseases of mental health. Key Concepts: During development sex‐specific hormones organize the brain into a male or female phenotype which is then activated by hormones in adulthood. The largest magnitude sex differences in the brain are in areas associated with control of reproduction. Hormones regulate growth factors, cell death, cell genesis and synaptogenesis to build sexually dimorphic neural circuits. There are multiple cellular mechanisms of hormonally mediated sexual differentiation which vary by brain region and endpoint. Because of the myriad of mechanisms and the impact of environment and experience, ultimately every brain is a moasic of masculine and feminine in varying degrees.

Regional brain development analysis through registration using anisotropic similarity, a constrained affine transformation

“…This is also notable in the same regions between 339 6 and 12 years, this time along direction 3. For the older class (12)(13)(14)(15)(16)(17)(18)(19), this phenomenon 340 essentially appears brainwise along the direction 3 and in the parietal lobes along 341 direction 1.…”