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Male and Female Brain Differences Evident in Earliest Days of Life

Brain differences between males and females are present from birth, according to a landmark study that examined brain scans of more than 500 newborns. The research, published in Biology of Sex Differences, provides new insights into early brain development and challenges previous assumptions about when sex-based brain differences emerge.

“Our study settles an age-old question of whether male and female brains differ at birth,” says lead author Yumnah Khan of the University of Cambridge’s Autism Research Centre. “We know there are differences in the brains of older children and adults, but our findings show that they are already present in the earliest days of life.”

The study analyzed brain scans from 514 healthy newborns, making it the largest investigation of its kind. Male infants showed larger overall brain volumes, even after accounting for differences in birth weight. However, when adjusting for total brain size, female infants had proportionally more gray matter, while males had more white matter.

“Because these sex differences are evident so soon after birth, they might in part reflect biological sex differences during prenatal brain development, which then interact with environmental experiences over time to shape further sex differences in the brain,” Khan explains.

The research team, using data from the Developing Human Connectome Project, found that females showed larger volumes in brain regions related to memory and emotional regulation, while males had larger volumes in areas involved in sensory processing and motor control.

Dr. Alex Tsompanidis, who supervised the study, emphasizes its methodological rigor: “This is the largest such study to date, and we took additional factors into account, such as birth weight, to ensure that these differences are specific to the brain and not due to general size differences between the sexes.”

The researchers caution against overgeneralizing these findings. “The differences we see do not apply to all males or all females, but are only seen when you compare groups of males and females together. There is a lot of variation within, and a lot of overlap between, each group,” notes Dr. Carrie Allison, Deputy Director of the Autism Research Centre.

Professor Simon Baron-Cohen, Director of the Autism Research Centre, adds context: “These differences do not imply the brains of males and females are better or worse. It’s just one example of neurodiversity. This research may be helpful in understanding other kinds of neurodiversity, such as the brain in children who are later diagnosed as autistic, since this is diagnosed more often in males.”

The research team is now investigating how prenatal conditions might contribute to these differences, examining factors such as hormones and placental development that could influence brain development before birth.


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