Differences in male and female brains ‘present at birth’, University of Cambridge researchers find
Differences in the structure of male and female brains are present from birth, research from the Autism Research Centre at the University of Cambridge has revealed.
Male brains tend to have a greater volume than female brains but when adjusted for size, female infants typically have significantly more grey matter. Male infants, meanwhile, were found on average to have significantly more white matter in their brains.
Grey matter, which comprises neuron cell bodies and dendrites, is responsible for processing and interpreting information, such as sensation, perception, learning, speech, and cognition.
White matter is made up of axons - long nerve fibres that connect neurons together from different parts of the brain.
The study was led by Yumnah Khan, a PhD student at the Autism Research Centre, who 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.”
Research in this field has been challenging to date because it has been difficult to get a large enough sample size.
But the Cambridge team analysed data from the Developing Human Connectome Project, through which infants receive an MRI brain scan soon after birth.
There were more than 500 newborn babies in the study, making it suitable for detecting sex differences.
However, studies in this area also have to take account of whether any observed sex differences are due to other factors, such as differences in body size.
The Cambridge researchers found that, on average, even after sex differences in birth weight were taken into account, male infants had significantly larger brain volumes.
After taking the volume difference into account, 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.
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 differences are averages, so do not apply in all cases.
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.”
Prof 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.”
The study, published in the journal Biology of Sex Differences, was funded by Cambridge University Development and Research, Trinity College, Cambridge, the Cambridge Trust, and the Simons Foundation Autism Research Initiative.