An over-hyped study claims brain differences underlie gender-specific behaviours.
You have most likely already heard of this study if you keep up to date with the science news. Published in PNAS, the authors report “hardwired” differences between the connections in male and female brains and claim these correlate with certain behaviours. Society is gender-obsessed and the science of gender differences is riddled with controversy. Is this just another example of the mass media and scientists over-interpreting these differences to fit in with the popular notion of gender stereotypes?
Nature versus nurture
Is gender predominantly defined by nature or nurture? There are subtle gender differences in the brain, and hormones that regulate reproduction are also important for gender-specific brain development and function. Although biology is an important influence, when it comes down to gender roles it may be upbringing that plays the most powerful role. It is, nonetheless, still unclear what the consequences of gender differences in the brain are.
The study in question
The study, published in PNAS last week, comprised 949 youths ranging from 8 to 22 years old. The authors used a technique called diffusion tensor imaging (DTI) to map the structural connections within and between the left and right hemispheres. Male brains reportedly showed more connections within hemispheres and female brains displayed more between the two hemispheres. The authors went on to conclude “male brains are structured to facilitate connectivity between perception and co-ordinated action, whereas female brains are designed to facilitate communication between analytical and intuitive processing modes”. Professor Verma, who led the study, later added in an interview that such intuitive behaviours in females are linked with good mothering skills. Such conclusions are, nonetheless, just assumptions as the authors did not measure behaviours in the present study.
What other experts in the field think..
Since the publication of the study, experts in the field have shared their thoughts on the study’s claims.
1. Correlating wiring with behaviour
The authors correlate these apparent differences in connectivity with cognition, but no effort was made to measure cognition. Professor Dorothy Bishop, based at University of Oxford, stated, “it is going well beyond the data to draw conclusions about the functional significance of these effects.”
Dr Adam Hampshire, a Senior Lecturer in Restorative Neurosciences at Imperial College London, said that such a conclusion “would require that correlations were examined between cognitive measures (e.g. working memory capacity) and connection strengths within [each] group”.
2. Brain size as a confounding factor
The technique used in the present study, DTI, is sensitive to the physical distance between connections and yet brain size was not considered here. Dr Adam Hampshire rightly points out “males tend to have slightly larger brains, which would certainly drive illusory differences in connectivity”.
3) Experience-dependent brain plasticity
The authors claim “hardwired” differences in connections exist between the genders, but this is completely misleading. Professor Heidi Johansen-Berg from the University of Oxford stated, “we know that there is no such thing as ‘hard wiring’ when it comes to brain connections. Connections can change throughout life, in response to experience and learning”. Indeed, brain connections are constantly forming, strengthening, weakening and degrading.
So perhaps these subtle gender differences in brain structure are due to differences in upbringing; an individual’s gender has a large impact on their experiences such as education, hobbies, and sport activities.
Evidently, it is easy to draw the wrong conclusions. The majority of the news articles covering the study content further exaggerated the far-fetched conclusions to help explain the popular notion that men are from Mars and women are from Venus. Whether that notion holds any truth or is entirely delusional is something we are yet to find out.
Photo: Flickr, loop_oh
Ingalhalikar M, Smith A, Parker D, Satterthwaite TD, Elliott MA, Ruparel K, Hakonarson H, Gur RE, Gur RC, & Verma R (2013). Sex differences in the structural connectome of the human brain. Proceedings of the National Academy of Sciences of the United States of America PMID: 24297904
Brain, differences, females, gender, males, Nature, nurture, sex