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Several things went wrong in the early days of sex differences and brain imaging research. With respect to sex differences, there was a frustrating backward focus on historical beliefs in stereotypes (termed "neurosexism" by psychologist Cordelia Fine). Studies were designed based on the go-to list of the "robust" differences between females and males, generated over the centuries, or the data were interpreted in terms of stereotypical female/male characteristics which may not have even been measured in the scanner. If a difference was found, it was much more likely to be published than a finding of no difference, and it would also breathlessly be hailed as an "at last the truth" moment by an enthusiastic media. Finally the evidence that women are hard-wired to be rubbish at map reading and that men can't multi-task! So the advent of brain imaging at the end of the 20th century did not do much to advance our understanding of alleged links between sex and the brain.
Here in the 21st century, are we doing any better?
One major breakthrough in recent years has been the realisation that, even in adulthood, our brains are continually being changed, not just by the education we receive, but also by the jobs we do, the hobbies we have, the sports we play. The brain of a working London taxi driver will be different from that of a trainee and from that of a retired taxi driver; we can track differences among people who play videogames or are learning origami or to play the violin. Supposing these brain-changing experiences are different for different people, or groups of people? If, for example, being male means that you have much greater experience of constructing things or manipulating complex 3-D representations (such as playing with Lego), it is very likely that this will be shown in your brain. Brains reflect the lives they have lived, not just the sex of their owners.
Seeing the life-long impressions made on our plastic brains by the experiences and attitudes they encounter makes us realise that we need to take a really close look at what is going on outside our heads as well as inside. We can no longer cast the sex differences debate as nature versus nurture - we need to acknowledge that the relationship between a brain and its world is not a one-way street, but a constant two-way flow of traffic.
Once we acknowledge that our brains are plastic and mouldable, then the power of gender stereotypes becomes evident. If we could follow the brain journey of a baby girl or a baby boy, we could see that right from the moment of birth, or even before, these brains may be set on different roads. Toys, clothes, books, parents, families, teachers, schools, universities, employers, social and cultural norms - and, of course, gender stereotypes - all can signpost different directions for different brains.
Resolving arguments about differences in the brain really matters. Understanding where such differences come from is important for everyone who has a brain and everyone who has a sex or a gender of some kind. Beliefs about sex differences (even if ill-founded) inform stereotypes, which commonly provide just two labels - girl or boy, female or male - which, in turn, historically carry with them huge amounts of "contents assured" information and save us having to judge each individual on their own merits or idiosyncrasies.
With input from exciting breakthroughs in neuroscience, the neat, binary distinctiveness of these labels is being challenged - we are coming to realise that nature is inextricably entangled with nurture. What used to be thought fixed and inevitable is being shown to be plastic and flexible; the powerful biology-changing effects of our physical and our social worlds are being revealed.
The 21st century is not just challenging the old answers - it is challenging the question itself.
An extract from The Gendered Brain by Gina Rippon.