Does this complicated-sounding list of brain activations tell us something interesting about gender difference in emotional experience? The researchers, like Pinker, certainly think so. They conclude that their ‘findings suggest that men tend to modulate their reaction to stimuli, and engage in analysis and association, whereas women tend to draw more on primary emotional reference.’31 (By this they mean that only women find others’ emotions innately arousing.) As you will have already realised, a simpler, and more familiar, way to put the same idea would be to say that men are thinkers and women are feelers.
So does this neuroimaging study simply confirm what everyone already suspected – that ‘men may take a more analytic approach’ to emotion processing while ‘women are more emotionally centred’?32 Or is it possible that these interpretations are, to paraphrase Fausto-Sterling, unwittingly projecting assumptions about gender onto the vast unknown that is the brain?
With the previous chapter’s cautionary tale of premature speculation in mind, it’s worth noting that Witelson’s neuroimaging study compared just eight men with eight women on each task – a modest-sized sample. Could the sex differences in brain activation be spurious? When looking for changes in blood flow between two conditions, researchers search in thousands of tiny sections of the brain (called voxels), and many researchers are now arguing that the threshold commonly set for declaring that a difference is ‘significant’ just isn’t high enough. To illustrate this point, some researchers recently scanned an Atlantic salmon while showing it emotionally charged photographs. The salmon – which, by the way, ‘was not alive at the time of scanning’ – was ‘asked to determine what emotion the individual in the photo must have been experiencing.’ Using standard statistical procedures, they found significant brain activity in one small region of the dead fish’s brain while it performed the empathising task, compared with brain activity during ‘rest’. The researchers conclude not that this particular region of the brain is involved in postmortem piscine empathising, but that the kind of statistical thresholds commonly used in neuroimaging studies (including Witelson’s emotion-matching study) are inadequate because they allow too many spurious results through the net.33
This of course does not mean that all reported activations are spurious. It just highlights the importance of being aware of the possibility. We might be more confident that Witelson’s study genuinely identified brain regions that function differently in the two sexes during emotion recognition tasks if at least some of the brain regions that showed sex differences in activation in the easy emotion-matching tasks also turned up in the harder task.34 However, if you look back at the list of brain activations you’ll see that in neither men nor women was any brain region activated more during both the easy and difficult emotion-matching tasks.
But even if we assume that results such as these are reliable, what do they tell us about male/female differences in psychology? Does it mean that men are more analytic, if their left inferior frontal gyrus activates more, or that women are more emotional because the right amygdala is on fire? Inferring a psychological state from brain activity (like The amygdala was activated so that means our participants were fearful) is known as reverse inference, and as any neuroimager will tell you, it is fraught with peril.35 Some neuroscientists have even died while making reverse inferences. Actually, I made that last bit up, but as we will see, it is extremely tricky. There are two ways that males and females can diverge in brain activation: how much activation is seen and where that activation is. Neither piece of information, unfortunately, tells us much about psychological sex differences.
Just as bigger doesn’t necessarily mean better with regards to the size of brain structures, neither does more activation necessarily mean better or psychologically more. Researchers who study development, or learning, sometimes find that some patterns of activation reduce, or become more streamlined, as development or expertise proceeds.36 Bizarrely, activation isn’t even a surefire sign that the activity is doing anything useful. For example, Chris Bird and colleagues studied a patient who suffered extensive damage to the medial prefrontal cortex following a stroke. The scope of the damage included pretty much all of the brain regions that have been reliably activated in literally dozens of functional imaging studies of mind reading. Yet the patient was fine at mind reading! As the researchers note, ‘the data reported here urge caution in concluding that medial frontal cortex is critical for effecting ToM [theory of mind]’.37 Vision scientist Giedrius Buracas and colleagues had an equally surprising finding. They found that brain region V1 was activated more than region MT in a motion perception task. Yet it’s well-established from neurophysiological research with primates that MT – which was activated less – is critically involved in motion detection, while V1 – which was activated more – is not.38 These two studies serve as warning flags: even though a part of the brain might light up during a task, it may not be especially or crucially involved.
The location of activation in the brain is also surprisingly uninformative. Clearly, the whole brain isn’t involved in doing everything. Different parts of the brain are specialised for processing different sorts of information. But a particular cortical region or population of neurons can be specialised for different jobs in different contexts. As imaging experts Karl Friston and Cathy Price put it, specialisation is dynamic and context-dependent.39 For example, a particular population of neurons in the temporal cortex may, at different times, represent both identity (Whose face is it?) and expression (Is it happy or sad?). What those neurons are doing depends both on what sort of information is being fed in, and also what sort of information is being fed back from higher regions in the processing chain. ‘Specialisation is therefore not an intrinsic property of any region’, argue Price and Friston, and that means that seeing a brain region in action doesn’t mean you know what it’s up to in your particular task. For many parts of the brain, this problem is acute. For example, the anterior cingulate is activated by so many tasks that one cognitive neuroscientist I know refers to it as the ‘on button’.
There just isn’t a simple one-to-one correspondence between brain regions and mental processes, which can make interpreting imaging data a difficult task. As Jonah Lehrer recently explained in the Boston Globe:
[O]ne of the most common uses of brain scanners – taking a complex psychological phenomenon and pinning it to a particular bit of cortex – is now being criticized as a potentially serious oversimplification of how the brain works.… [C]ritics stress the interconnectivity of the brain, noting that virtually every thought and feeling emerges from the crosstalk of different areas spread across the cortex.40
If so, the familiar spots of colour on brain activation maps (derided by some as ‘blobology’), labelled as male-female difference in activation, are going to tell a very oversimplified story, and one in which much of the important information may be lost. It’s also a story that, as neuropsychologist Anelis Kaiser and colleagues point out, is geared to emphasise difference over similairy.41
Then, there is the sad fact that, at its most precise, functional imaging technology averages over a few seconds the activity of literally millions of neurons that can fire up to a hundred impulses a second. (For PET the time-scale is even longer.) ‘Using fMRI to spy on neurons is something like using Cold War–era satellites to spy on people: Only large-scale activity is visible’, says Science journalist Greg Miller.42 This severely limits the interpretations that can be made about brief psychological events. Understandably, given all these interpretative gaps, many neuroscientists hesitate to speculate what their data might mean in terms of sex differences in thinking. Many, to their credit, have performed admirably as The Voice of Restraint in popular articles about gender and the brain, and in their academic work explicitly warn against making unwarranted inferences (pleas that, in certain quarters, fall on deaf ears).
It’s not, by the way, my intention to present myself as a neuroscience sceptic. Not only are some of my best f
riends, as well as family members, neuroimagers, but I also think that neuroscience is an extremely exciting and promising field, and can be usefully employed in combination with other techniques. I also understand that speculation is an important part of the scientific process. Nor is the topic of gender difference by any means the only area in which overinterpretation can occur. And I certainly don’t think that research into sex differences in the brain is wrong or pointless. There are sex differences in the brain (although, as we’ve seen, agreeing on what these are is harder than you might think);43 there are sex differences in vulnerabilities to certain psychological disorders, and hopefully greater understanding of the former might help to illuminate the latter. My point is simply this: that neither structural nor functional imaging can currently tell us much about differences between male and female minds. As Rutgers University psychologist Deena Skolnick Weisberg has recently argued, we should ‘remember that neuroscience, as a method for studying the mind, is still in its infancy. It shows much promise to be someday what many people want to make it into now: a powerful tool for diagnosis and research. We should remember that it has this promise, and give it the time it needs to achieve its potential – without making too much of it in the meantime.’44
Are early twenty-first-century neuroscientific explanations of inequality – too little white matter, an unspecialised brain, too rapacious a corpus callosum – doomed to join the same garbage heap as measures of snout elongation, cephalic index and brain fibre delicacy? Will future generations look back on early twenty-first-century interpretations of imaging data with the same shocked amusement with which we regard early twentieth-century speculations about the relevance of sex differences in spinal cord size? I suspect they will, although only time will tell. But to any scientist considering trying to relate sex differences in the brain to complex psychological functions … well, let’s just say, ‘Remember Dr. Charles Dana’.
And it is important to remember him. For as we’ll see in the next chapter, the speculations of a few scientists quickly evolve into the colourful fabrications of popular neurosexism – the subspecialty within the larger discipline of neurononsense to which we now turn.
My husband would probably like you to know that, for the sake of my research for this chapter, he has had to put up with an awful lot of contemptuous snorting. For several weeks, our normally quiet hour of reading in bed before lights out became more like dinnertime in the pigsty as I worked my way through popular books about gender difference. As the result of my research, I have come up with four basic pieces of advice for anyone considering incorporating neuroscientific findings into a popular book or article about gender: (1) unless you have a time machine and have visited a future in which neuroscientists can make reverse inferences without the nagging anxieties that keep the more thoughtful of them awake at night, do not suggest that parents or teachers treat boys and girls differently because of differences observed in their brains; (2) if you don’t know what a reverse inference is, read the previous chapter of this book; (3) exercise extreme caution when making the perilous leap from brain structure to psychological function; and (4) don’t make stuff up.
When it comes to selecting examples from those who have failed to follow one or more of these four simple rules, one’s choices abound. Possibly my favourite illustration of a self-serving projection of prejudices onto brain jargon is a section in John Gray’s Why Mars and Venus Collide in which he discusses the inferior parietal lobe (IPL). In men, says Gray, the left IPL is more developed, while in women it is the right side that is larger. It will be no surprise to anyone, I am sure, to learn that ‘[t]he left side of the brain has more to do with more linear, reasonable, and rational thought, while the right side of the brain is more emotional, feeling, and intuitive.’ But it is extraordinary just how differently the IPL serves its master and its mistress. According to Gray a man’s large left IPL, being involved in the ‘perception of time’, explains why he becomes impatient with how long a woman talks. By contrast, the IPL also ‘allows the brain to process information from the senses, particularly in selective attention, like when women are able to respond to a baby’s crying in the night.’1 Perhaps deliberately, we are left in the dark as to whether the male inferior parietal lobe enables a man to do the same.
In Leadership and the Sexes, Michael Gurian and Barbara Annis inform executives that ‘women’s brains tend to link more of the emotional activity that is going on in the middle of the brain (the limbic system) with thoughts and words in the top of the brain (the cerebral cortex). Thus a man might need many hours to process a major emotion-laden experience [I … just … got … fired.… I … am … sad … and … angry.], whereas a woman may be able to process it quite quickly [Oh, crap!].’2 A further neurophysiological disadvantage for men may be found in another of Gurian’s books, What Could He Be Thinking? Implicitly drawing on a working metaphor of The Brain as Pinball Machine, he explains how in men the ‘signal’ of an emotional feeling, having made it to the right hemisphere, ‘may well get stopped, disappearing into neural oblivion because the signal found no access to a receptor in a language center in the left side of the brain.’ This doesn’t happen in the female brain because, according to Gurian, while men have just one or two language centres in the left hemisphere, women have as many as seven such centres, dotted all over the brain, as well as a 25 percent larger corpus callosum. (Despite this embarrassment of neurological riches, the contrast Gurian draws between male and female brain function leaves me speechless.) And so, in men, a feeling signal is much less likely to hit the jackpot of contact with a neuron involved in language.3
We also discover in Leadership and the Sexes that when a woman leader asks her colleagues, ‘What do you all think?’ this is a typically female ‘white matter’ question. It seems that white matter isn’t just involved in integrating information from different parts of the brain, but also from different people in the office.4 Brain differences may also be behind a female-leadership problem-solving style: when a female leader ‘knows what to do, she’s not as worried as a man might be about proving it with data’. Gurian and Annis suggest that ‘[o]ne reason for this intuitiveness may be that she has a larger corpus callosum connecting both hemispheres of the brain’. By contrast, male leaders favour a problem-solving style that, in part, ‘relies on more linear data and proof.’5
Perhaps my own corpus callosum runs to a smaller size than the standard female issue, but I find these intuitive leaps from brain structure to psychological function unconvincing, as noted in the previous chapter. Why should arriving at a solution to a problem through an analysis of data and proof require any less integration between hemispheres? As an example of just how wrong our intuitions can be in these matters, despite the popular assumption that a more lateralised brain will be worse at multitasking, neurobiologist Lesley Rogers and her colleagues found precisely the opposite to be the case in chicks.6 Chicks with more lateralised brains were better at simultaneously pecking for food grains and looking out for predators (the established chick equivalent of frying a steak while making a salad).
While it may not be too surprising to discover self-appointed ‘thought-leaders’ dressing up stereotypes in neuroscientific finery, it is more of a shock to see this in an alumnus of Harvard Medical School, the University of California–Berkeley, and Yale School of Medicine. Step forward Louann Brizendine, director of the University of California–San Francisco Women’s Mood and Hormone Clinic. Her book, The Female Brain, cites literally hundreds of academic articles. To the unwary reader, both she and the book seem reliable and authoritative. And yet, as a review of the book in Nature comments, ‘despite the author’s extensive academic credentials, The Female Brain disappointingly fails to meet even the most basic standards of scientific accuracy and balance. The book is riddled with scientific errors and is misleading about the processes of brain development, the neuroendocrine system, and the nature of sex differences in general.’ The reviewers later go on to say that,
‘[t]he text is rife with “facts” that do not exist in the supporting references.’7 This is a common discovery made by people who take the time to fact-check Brizendine’s claims. Mark Liberman, a professor at the University of Pennsylvania with no special interest in gender issues, has nonetheless been provoked to provide many detailed but humorous critiques of pseudoscientific claims about gender differences on his online Language Log. His patient corrections of Brizendine’s many false assertions about sex differences in communication is a chore that, as he puts it, ‘is starting to make me feel like the circus clown that follows the elephant around the ring with a shovel.’8
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