fMRI shows male, female brains going separate ways in the womb

Using resting-state functional MRI (fMRI) to image the brains of human fetuses in utero, researchers have confirmed that functional connectivity differs between the sexes from very early on in neurodevelopment.

“Specifically, female fetuses demonstrated long range gestational-age related changes in functional connectivity between subcortical and cortical regions,” the authors reported in the April edition of Developmental Cognitive Neuroscience. “This pattern of functional connectivity-gestational age relationships within these network pairs [was] almost completely non-existent in male fetuses.”

Corresponding author Adam Eggebrecht, PhD, of the Mallinckrodt Institute of Radiology at Washington University in St. Louis and colleagues made their observations using fMRI to study functional connectivity in 118 human fetuses (70 male, 48 female) between 25.9 and 39.6 weeks gestational age. The study subjects’ mothers were recruited during routine obstetric appointments. (The pre-exclusion cohort numbered 166.)  

Looking at 16 distinct fetal neural networks distributed throughout the cortex and subcortical regions, the team recorded differences between male and female fetuses in functional connectivity within and between seven networks across gestational age.

“These observations confirm that sexual dimorphism in functional brain systems emerges during human gestation,” the authors concluded.  

In their discussion, Eggebrecht and colleagues noted the consistency of their findings with meta analyses of neurodevelopmental sex differences in infants. They cited prior research showing female infants have greater volume within the dorsolateral prefrontal cortex and visual cortex.

“It seems likely that these volumetric differences are mirrored by superior frontal gyrus functional-connectivity differences observed in the present study,” Eggebrecht and colleagues wrote.

The team acknowledged several limitations in their study design. One owed to the challenges of imaging fidgeting patients in the womb. In this case such movement precluded the use of standard segmentation and reorientation algorithms, forcing the researchers to perform manual segmentation and reorientation for calculating blood-oxygen-level dependent volumes.

“Future analyses with this data may endeavor to automate this process with computer routines and algorithms catered to this unique dataset,” they wrote.

The work quickly caught the eye of the consumer press (example) and will likely spur lively discussions on social media.