03 December 2013

Sex on the Brain: Are Male and Female Brains Fundamentally Different?

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You have heard it in the shrill media. The science is in. It’s connectomically done and dusted: men’s brains are wired for spatial tasks like map-reading, women’s brains are wired for those ‘soft skills’ like empathising with jilted friends at the water-cooler.

Recent headlines on this subject arose from a press release issued by Penn Medicine about a new study published in the Proceedings of National Academy of Sciences[i] that shows, in the words of the press release, ‘striking differences in the neural wiring of men and women that’s lending credence to some commonly-held beliefs about their behavior.’

Though given a quick veneer of sobriety, the take on the study published in The Guardian was fairly typical of the kind of schematic-obsessed journalism spawned: ‘Maps of neural circuitry show women's brains are suited to social skills and memory, men's perception and co-ordination’, asserted its strapline. The Independent went with, ‘The hardwired difference between male and female brains could explain why men are 'better at map reading'’, followed, sotto voce, by, ‘And women are 'better at remembering a conversation'’.

Neither the abstract of the study paper nor the Penn Medicine press release actually mention ‘hardwiring’, so I was slightly surprised to note one of the paper’s contributors, Ragini Verma PhD, using the term. She is quoted in The Guardian as saying, ‘If you look at functional studies, the left of the brain is more for logical thinking, the right of the brain is for more intuitive thinking. So if there's a task that involves doing both of those things, it would seem that women are hardwired to do those better.’

The study used a technique called diffusion tensor imaging (DTI) to map the diffusion paths of water molecules within the brains of 428 males and 521 females aged between 8 and 22 years. The technique reveals the main fibre pathways, allowing the inference of major connections between brain regions. (I have used the word ‘inference’ to stress that DTI cannot reveal full connectomic maps. In the words of the press release, it is ‘laying the foundation for a structural connectome or network of the whole brain.’) The results showed that the main fibre bundles in the male brains tended to run from front to back of each hemisphere, whereas in the females there tended to be a higher degree of interconnection between left and right hemispheres. The study also showed only slight differences between male and female connectomes in children younger that 13 years, but differences becoming markedly more pronounced in adolescents over the age of 14.

Don’t get me wrong, connectomes fascinate me. And understanding that we are the wiring of our brains is essential to the wider task of clearing away residual dualism, allowing us to build better systems of justice, a healthier citizenry, and fairer societies based upon biological facts, not upon ‘gut instincts’. However, these connectome-based studies are only an initial foray into this extremely complex field. We must always consider the fact of brain plasticity when looking at studies that show differences in connectivity. If male and female connectomes tend to be quite different, how do they get that way? Just how closely do the connectomic differences map to actual differences in cognitive function? Another contributor to the study, Dr. Ruben Gur, seems a little more circumspect about where we are now: ‘Detailed connectome maps of the brain will not only help us better understand the differences between how men and women think, but it will also give us more insight into the roots of neurological disorders, which are often sex related.’

Other factors to take into account are, as usual, the makeup of the sample and the strength of the correlations found. In any human study, we need to know that the sample is representative of the group in question. In this case, the group is the entire human race, so it is vital that the genetic and cultural diversity of that group is reflected in the study. As to correlation strength, whenever we are told that X means Y we need to know to what extent X suggests Y and vice versa (the correlation coefficient). Here we are being told that differences between the pathways of the main fibre bundles in the brains of males and females mean that there are major differences in the specialisation of cognitive skills in men and women; we can learn something about X with diffusion tensor imaging, but Y involves testing and measurement of cognitive skills, which is fraught with problems. Neither the abstract nor the press release (and certainly not the newspaper articles) provide us with such a correlation coefficient.

The media tends to treat scientific studies as if they trump each other. Unless we take into account the results of other properly-conducted studies designed to address the same kinds of questions, we run the risk of seeing each new result as the definitive one. Overview-type papers taking into account the results of various studies and experiments can help us to appreciate the subtlety of scientific discourse. In ‘Male or Female? Brains are Intersex[ii], for example, Joel argues that, because of the myriad genetic and environmental factors involved, ‘we cannot predict the particular array of “male/female” brain characteristics of an individual on the basis of her/his sex.’

If you now feel that this issue has become a bit of a fudge, then perhaps that’s a reasonable analogy. There are various ingredients in the mix, including the sugar of genetics, the milk of environment, and the butter of random connectomic change. I’ll admit that, as a transhumanist, I am drawn to explanations that allow us the most degrees of freedom about what we may become and what skills we can learn. Nonetheless, I think it is fair to say that the science to date does not prove that sex trumps plasticity when it comes to choosing our paths.

It may turn out that connectomes do indeed specialise and 'hardwire' into rigidly or semi-rigidly male or female configurations during adolescence, under all normal circumstances. But the data is not yet conclusive. Even if that does prove to be the case, the plasticity of our brains will always allow room for manoeuvre. Spend time reading maps each day and you will become better than average at reading maps. Listen sympathetically to people every day and you will become better than average at listening sympathetically to people. Even in older brains, the default-mode network (DMN) the 'resting state' configuration of neural connections – can be altered through practicing skills such as mindfulness.[iii] Despite this, most people would more readily attack the idea that we can learn to be more empathetic than the idea that we can learn better spatial skills, but is there a fundamental difference between such skills? Many responses to that question would include the word ‘natural’, but in this tangle of wiring, that will get us nowhere. We are certainly all wired (feel free to use a more naturalistic and less mechanistic word here) but we do not yet know to what extent we are either ‘hard’ or ‘soft’ wired.

It is difficult for us to shake our stereotypes, but they really are out of date. Neuroscience will unearth differences and commonalities in male and female brains, but it is up to us which we choose to focus upon. Do we wish to overlap, striving as human beings to be flexible, smart, logical, caring, tolerant, and likeable? Or do we wish to entrench ourselves, fearing the loss of stereotypical skills that we have considered important for the demarcation of our sexes?

Personally, I will focus on the overlaps between male and female cognition. 3-D empathy orienteering sounds like many hours of scary fun.

[i]    Madhura Ingalhalikar and others, ‘Sex Differences in the Structural Connectome of the Human Brain’, Proceedings of the National Academy of Sciences, 2013, 201316909 .
[ii]    Daphna Joel, ‘Male or Female? Brains Are Intersex’, Frontiers in Integrative Neuroscience, 5 (2011) .
[iii]   Ruchika Shaurya Prakash and others, ‘Mindfulness Disposition and Default-Mode Network Connectivity in Older Adults’, Social Cognitive and Affective Neuroscience, 8 (2013), 112–117.

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