Brain Connections Compared by Gender in Large-Scale Study

How do images of social brain and other connections compare across genders?

Posted Jan 06, 2019

A large-scale study of 5216 brains has found differences in the brains of men and women that might be linked to social and other abilities. Stuart Ritchie and coworkers reported in the 2018 journal Cerebral Cortex that women in this sample had more connections within the default mode network or DMN, which becomes active when other areas are at rest and which overlaps with a network of areas that help perceive and communicate with others by eye contact, facial expressions, and tone of voice in a social situation. According to the authors,

The higher female connectivity within circuits like the DMN may be particularly important, given that DMN regions are often considered as an important part of the “social brain.”

Although society has questioned stereotyping of female and male behavior, for thousands of years there has been an emphasis on females being especially good at nurturing and socializing with others. There remain gender differences in psychiatric disorders that encouraged the authors to investigate gender effects on brain connections using the latest methods. And while previous studies of this type have been criticized for their small sample size and use of only younger people, this study involved a large sample of adults above the age of 44.

For those who want more details, among possible social brain regions, two of them are the prefrontal cortex near the middle (medial) part of the brain measured from side to side, and the front part of the cingulate cortex, a band of grey matter found over the densely-packed nerve fibers that connect the left and right hemispheres together and form the corpus callosum. These regions stand out in Daniel Goleman’s book Social Intelligence, but there are several others, most likely interacting in a network under the right conditions.

The connections between brain areas, more properly termed connectivity, were analyzed with the recent method abbreviated as NODDI (for neurite orientation dispersion and density imaging), measures that can offer novel information on the direction of water molecules within and between nerve fibers, the long extensions of nerve cells that make up the white matter of the brain. You can think of more connectivity sending nerve signals faster the way several straws bundled together in a soft drink would let you slurp it up in a hurry.

Though this was an example of the statistical differences between genders in numerous measures, the authors are cautious in their interpretation, citing the large overlap, sometimes nearly 50 percent. As they point out:

For every brain measure that showed even large sex differences, there was always overlap between males and females...

They also point out that although their measures are biological, they still may be affected by upbringing and social factors.

In fact, recent evidence shows that practice by musicians and patients in physical therapy can influence brain connectivity (Ruber and others, 2015, and Zhang and Schlaug, 2015). One might extrapolate that other kinds of intensive practice, for example in social skills, might also strengthen pre-existing connections in the nervous system.

In a previous study of brain connectivity, with 949 young people between eight and 21, Dr. Ragini Verma and colleagues at the Perelman School of Medicine at the University of Pennsylvania also compared brain connectivity across genders.

They used the method of diffusion magnetic resonance imaging (dMRI) to analyze connectivity. They found more connectivity in women’s brains between the right hemisphere, thought to excel in detecting and expressing social information, and the left hemisphere, generally more important for understanding and speaking words and their combinations. The sample of women’s brains had more connections between each hemisphere, allowing the two halves of to communicate more easily.

The study, published the 2013 Proceedings of the National Academy of Sciences, found gender differences were more pronounced in teenagers than in younger children, suggesting an influence of puberty on brain development.

In this study, women performed better at recognizing faces and at social tasks, among other things. Think of interacting with others in a complex social situation.

The connections in their sample of male brains were greater between the front and back of each hemisphere. That includes the prefrontal area in front, which plays a role in planning and executing a series of tasks among other functions, the sensorimotor area near the middle, and the visual area in the back. An example would be reaction time to an object suddenly appearing in one’s field of view. A more complex example that combines prefrontal, sensorimotor, and visual functions might be assembling a bookcase from an instruction sheet, though this was definitely not part of these studies. And count this author out as a volunteer.

References

Daniel Goleman (2016), Social Intelligence: The new science of human relationships, pp .323-328, Bantam Books, New York.

Stuart J Ritchie and others, Sex Differences in the Adult Human Brain: Evidence: from 5216 UK Biobank Participants. Cerebral Cortex 28(1). https://academic.oup.com/cercor/article/28/8/2959/4996558

T. Ruber, R. Lindenberg,k and G. Schlaug (2015)  Differential adaptation of descending motor tracts in musicians. Cerebral Cortex 25(6).

X. Zhang and G. Schlaug (2015), White matter changes in descending motor tracts correlate withb improvements in motor impairment after undergoing  a treatment coure of tDCS and physical therapy. Frontiers in Human Neuroscience, April 30.