Summary: A study analyzing over 500 newborns has confirmed that brain structure differences between male and female infants are present from birth. While male brains were larger on average, females had more grey matter in regions related to memory and emotion, whereas males had more white matter and grey matter in sensory and motor regions.
These findings suggest that sex differences in the brain originate during prenatal development and interact with environmental factors over time. Researchers emphasize that these differences are averages and do not apply universally, highlighting the importance of understanding neurodiversity rather than assigning value to these differences.
Key Facts:
- Early Sex Differences: Male and female brain differences are evident at birth, suggesting prenatal origins.
- Distinct Brain Structures: Females show more grey matter in memory and emotional areas, while males show more white matter and sensory-motor grey matter.
- Neurodiversity Insight: Findings contribute to understanding conditions like autism, diagnosed more often in males.
Source: University of Cambridge
Sex differences in brain structure are present from birth, research from the Autism Research Centre at the University of Cambridge has shown.
While male brains tended to be greater in volume than female brains, when adjusted for total brain volume, female infants on average had significantly more grey matter, while male infants on average had significantly more white matter in their brains.
Grey matter is made up of neuron cell bodies and dendrites and is responsible for processing and interpreting information, such as sensation, perception, learning, speech, and cognition. White matter is made up of axons, which are long nerve fibres that connect neurons together from different parts of the brain.
Yumnah Khan, a PhD student at the Autism Research Centre, who led the study, said: “Our study settles an age-old question of whether male and female brains differ at birth. 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.
“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.”
One problem that has plagued past research in this area is sample size. The Cambridge team tackled this by analysing data from the Developing Human Connectome Project, where infants receive an MRI brain scan soon after birth.
Having over 500 newborn babies in the study means that, statistically, the sample is ideal for detecting sex differences if they are present.
A second problem is whether any observed sex differences could be due to other factors, such as differences in body size.
The Cambridge team found that, on average, male infants had significantly larger brain volumes than did females, and this was true even after sex differences in birth weight were taken into account.
After taking this difference in total brain volume into account, at a regional level, females on average showed larger volumes in grey matter areas related to memory and emotional regulation, while males on average had larger volumes in grey matter areas involved in sensory processing and motor control.
The findings of the study, the largest to date to investigate this question, are published in the journal Biology of Sex Differences.
Dr Alex Tsompanidis who supervised the study, said: “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.
“To understand why males and females show differences in their relative grey and white matter volume, we are now studying the conditions of the prenatal environment, using population birth records, as well as in vitro cellular models of the developing brain.
“This will help us compare the progression of male and female pregnancies and determine if specific biological factors, such as hormones or the placenta, contribute to the differences we see in the brain.”
The researchers stress that the differences between males and females are average differences.
Dr Carrie Allison, Deputy Director of the Autism Research Centre, said: “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 a variation within, and a lot of overlap between, each group.”
Professor Simon Baron-Cohen, Director of the Autism Research Centre, added: “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.”
Funding: The research was funded by Cambridge University Development and Research, Trinity College, Cambridge, the Cambridge Trust, and the Simons Foundation Autism Research Initiative.
About this neurodevelopment and brain mapping research news
Author: Craig Brierley
Source: University of Cambridge
Contact: Craig Brierley – University of Cambridge
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Sex differences in human brain structure at birth” by Yumnah Khan et al. Biology of Sex Differences
Abstract
Sex differences in human brain structure at birth
Background
Sex differences in human brain anatomy have been well-documented, though remain significantly underexplored during early development. The neonatal period is a critical stage for brain development and can provide key insights into the role that prenatal and early postnatal factors play in shaping sex differences in the brain.
Methods
Here, we assessed on-average sex differences in global and regional brain volumes in 514 newborns aged 0–28 days (236 birth-assigned females and 278 birth-assigned males) using data from the developing Human Connectome Project. We also assessed sex-by-age interactions to investigate sex differences in early postnatal brain development.
Results
On average, males had significantly larger intracranial and total brain volumes, even after controlling for birth weight. After controlling for total brain volume, females showed significantly greater total cortical gray matter volumes, whilst males showed greater total white matter volumes.
After controlling for total brain volume in regional comparisons, females had significantly increased white matter volumes in the corpus callosum and increased gray matter volumes in the bilateral parahippocampal gyri (posterior parts), left anterior cingulate gyrus, bilateral parietal lobes, and left caudate nucleus.
Males had significantly increased gray matter volumes in the right medial and inferior temporal gyrus (posterior part) and right subthalamic nucleus.
Effect sizes ranged from small for regional comparisons to large for global comparisons. Significant sex-by-age interactions were noted in the left anterior cingulate gyrus and left superior temporal gyrus (posterior parts).
Conclusions
Our findings demonstrate that sex differences in brain structure are already present at birth and remain comparatively stable during early postnatal development, highlighting an important role of prenatal factors in shaping sex differences in the brain.
