September 10, 2006

Open-access sex stereotypes

More precisely, open access to scientific articles cited in support of genetically-determined sex roles. That's what Robin Marantz Henig needed, in preparing her review of Louann Brizendine's The Female Brain ("How Women Think", New York Times Book Review, 9/10/2006).

With better access to the references, Henig might not have so easily accepted things that she should have questioned:

The hard-wiring occurs during fetal development, when brains are exposed to either male or female hormones beginning in about the eighth week of pregnancy. Testosterone prunes away the connections in the communication centers of the brain, while estrogen enhances these connections, as well as the regions of the brain responsible for language and for expressing emotion and observing it in others. These differences, Brizendine writes, make women better negotiators and conciliators, and men better fighters and lone wolves. (They also account for some of the author’s favorite factoids: for example, that men use 7,000 words per day and women use 20,000.)

As discussed at tedious length in earlier Language Log posts (e.g. "The laconic rapist in the womb", 9/4/2006), it's not clear that any of this neuro-sexual stereotyping is really true -- at least, Brizendine's references to the scientific literature don't actually provide support for it, and there are reasons to think that much of it is false or at least misleading. Later in the review, Henig complains about the difficulty of finding the connections between Brizendine's rhetoric and her science, and hints that the connections might sometimes be weak or absent:

If you want data to support some of Brizendine’s more controversial claims, you have to work hard to find it. Take, for instance, the statement that “studies indicate that girls are motivated — on a molecular and a neurological level — to ease and even prevent social conflict.” The endnote lists nine scholarly articles, with no further explanation given. From the titles (which the reader has to look for in the bibliography), we can surmise that one study was on female mice, one on male and female rats, one (apparently) on female rhesus monkeys, and the other six on humans. But only one of those human studies explicitly mentions “sex differences” in the title. What about the others? And are the studies based on M.R.I.’s, electroencephalograms, conjecture? If Brizendine had chosen to describe more of these experiments, preferably in the text itself, she might have made a real contribution to our understanding of how scientists know that male and female brains are different, and how these differences manifest themselves in everyday life. As it is, we’re unable to judge the evidence for ourselves. After all, if we’re going to engage in debates about female scientists (and female presidents), we need all the objective ammunition we can get.

I agree 100% with Henig's observation that "if we’re going to engage in debates about female scientists (and female presidents), we need all the objective ammunition we can get". So to further such debate, I've placed copies of eight of the nine of the cited papers on my own website, and linked to those open-access copies from a list given below, so that you can read them and check the summaries that I provide. (One of the nine is missing, because Penn lacks a subscription to the journal where it was published -- in that case, I've provided a link to the abstract on the publisher's site, and you can buy the 8-page article for $30 if you really want to.)

The point is not that these particular papers are crucial to the debate. As we'll see, alas, they're all irrelevant to the points that Brizendine cites them to support. However, you can't have a fair debate if one side gets to invoke the authority of science by reference to articles that the other side can't access. And every one of these articles represents research paid for by public funds. (At least, that's where funding for most published science of this sort comes from. I didn't check these cases in detail, and it's possible that some foundation money was also involved.)

The passage that Henig quotes is on p. 40, under the heading "Fear of Conflict", and it starts like this:

Studies indicate that girls are motivated -- on a molecular and a neurological level -- to ease and even prevent social conflict. Maintaining the relationship at all costs is the female brain's goal. This may be especially true in the teenage female brain.

The end-note for this on page 196, and cites nine references, just as Henig says:

Jasnow 2006; Bertolino 2005; Hamann 2005; Huber 2005; Pezawas 2005; Sabatinelli 2005; Viau 2005; Wilson 2005; Phelps 2004.

Working through a second level of indirection in Brizendine's bibliography, we can resolve these to:

1. Jasnow, A.M. et al. (2006), "Estrogen facilitates fear conditioning and increases corticotropin-releasing hormone mRNA expression in the central amygdala in female mice", Horm Behav 49(2):277-86.
2. Bertolino et al. (2005), "Variation of human amygdala response during threatening stimuli as a function of 5'HTTLPR genotype and personality style", Biol Psychiatry 57(12): 1516-25.
3. Hamann (2005), "Sex differences in the responses of the human amygdala", Neuroscientist 11(4):288-93.
4. Huber et al. (2005), "Vasopressin and oxytocin excite distinct neuronal populations in the central amygdala", Science 308(5719): 245-48.
5. Pezawas et al. (2005), "5-HTTLPR polymorphism impacts human cingulate-amygdala interactions: A genetic susceptibility mechanism for depression", Nat Neurosci 8(6): 828-34.
6. Sabatinelli et al. (2005), "Parallel amygdala and inferotemporal activation reflect emotional intensity and fear relevance", Neuroimage 24(4): 1265-70.
7. Viau et al. (2005), "Gender and puberty interact on the stress-induced activation of parvocellular neuroscretory neurons and corticotropin-releasing hormone messenger ribonucleic acid expression in the rat", Endocrinology 146(1): 137-46.
8. Wilson et al. (2005), "Gonadal steroid modulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis is influenced by social status in female rhesus monkeys", Endocrine 26(2): 89-97. (journal link)
9. Phelps (2004), "Human emotion and memory: Interactions of the amygdala and hippocampal complex". Curr Opin Neurobiol 14(2): 198-202.

My summaries of these articles, in the context of Brizendine's claims:

1. Jasnow 2006: shows that "long-term estrogen treatment in ovariectomized female mice via Silastic capsule implantation [faciliated] both contextual and cued fear conditioning". By "fear conditioning" they mean teaching individual mice to "freeze" in anticipation of electric shocks delivered via a test cage shock floor. Nothing here about social conflict avoidance or preserving relationships or humans of any sex.

2. Bertolino 2005: fMRI of 14 phobic-prone subjects and 14 eating-disorder-prone subjects showed that "phobic prone subjects selectively recruit the amygdala to a larger extent than eating disorders prone subjects". The level of amygdala activity "was also independently predicted by personality style and genotype of the serotonin transporter". In each group of 14, 9 were female and 5 were male, and the results are not differentiated by sex. Nothing here about social conflict or preserving relationships or teenagers of any sex.

3. Hamann 2005: A review article on sex differences in amygdala response. Connects the amygdala to women's "stronger and more vivid memories for emotional events" and to "the greater role that visual stimuli play in male sexual behavior". Male amydala is bigger. Abnormal amygdala response has been observed in depression. Speculates about relation to sex differences in rates of PTSD and voyeurism. Nothing here about social conflict avoidance or preserving relationships or teenagers.

4. Huber 2005: After determining "the distribution of vasopressin and oxytocin receptors in the CeA [central amygdala] using autoradiography on horizontal rat brain sections", they used intracellular recording to "find that vasopressin and oxytocin modulate activity in CeM neurons in opposite ways through the activation of distinct elements of an inhibitory network" and that "can differently affect the integration of distinct afferents to the CeA into a common output to the autonomic nervous system, thus providing a neurophysiological mechanism for their opposite effects on anxiety and fear behavior". Nothing here about sex differences, about social conflict avoidance, about preserving relationships, or about humans of any age or sex.

5. Pezawas 2005: They used "used multimodal neuroimaging in a large sample of healthy human subjects" to explore the basis of "increased anxiety-related temperamental traits, increased amygdala reactivity and elevated risk of depression" in "carriers of the short allele of a functional 5' promoter polymorphism of the serotonin transporter gene". They found "reduced gray matter volume in short-allele carriers in limbic regions critical for processing of negative emotion, particularly perigenual cingulate and amygdala". There were 114 subjects. They don't break their data down by sex, although they correlate genotyping and structural imaging with functional imaging results and also with personality-assessment questionnaires. Nothing here about sex differences, about social conflict avoidance, about preserving relationships, or about teenage girls.

6. Sabatinelli 2005: Looked at "functional activity in the visual cortex and amygdala with fMRI while selected fearful and control participants view a range of neutral, emotionally arousing, and fear-relevant pictures", and found an "individually-sensitive, positive linear relationship between the arousing quality of visual stimuli and activation in amygdala and ventral visual cortex". Subjects were 18 females from an undergrad psych course, half selected for "high snake fear". Stimuli were 60 color pictures showing "complex neutral scenes, neutral people, non-threatening animals, snakes, erotica, and mutilations". You'll never guess: "participants reporting elevated snake fear were more reactive while viewing pictures of snakes than unselected volunteers". Nothing here about sex differences or social conflict avoidance or preserving relationships.

7. Viau 2005: "To explore the nature by which gender differences in HPA [hypothalamic-pituitary-adrenal] function emerge we examined in prepubertal (~30-d-old) and postpubertal (~60-d-old) male and female rats HPA activity under basal conditions and in response to 30 min of restraint." They found sex and age differences, and concluded that "gonadal regulation of the HPA axis develops via distinct mechanisms" in male and female rats. Nothing here about social conflict avoidance or about preserving relationships.

8. Wilson 2005: They tested 4 dominant and 3 subordinate female rhesus monkeys, and found that estradiol replacement increased plasma levels of cortisol compared to a placebo and treatment with P4. Because Penn lacks a subscription to this journal, and I was unwilling to pay $30 for a 7-page article, I'm not sure about the details. Unlike the other articles cited, it does have something to do with social interaction, but there's apparently no direct relevance to social conflict avoidance or preserving relationships.

9. Phelps 2004: A review article about how the amygdala and the hippocampal complex interact: "the amygdala can modulate both the encoding and the storage of hippocampal-dependent memories. The hippocampal complex, by forming episodic representations of the emotional significance and interpretation of events, can influence the amygdala response when emotional stimuli are encountered." Discussion of sex differences is interesting but equivocal: "Recent brain imaging studies have suggested that the left and right amygdala could be differentially involved in memory for emotional stimuli depending on the sex of the subject. Specifically, two recent studies have shown that the left amygdala is correlated with later memory for emotional stimuli in female subjects, whereas the right amygdala is correlated with memory for emotional stimuli in male subjects" [...] "However, studies examining emotional memory or physiological responses to emotional stimuli in patients with amygdala damage have failed to find such sex differences. These studies have tended to be consistent with previous studies on hippocampal function showing a material specific involvement of the left and right amygdala for verbal and visual material, respectively." Nothing here about social conflict avoidance or preserving relationships.

Brizendine cites these nine studies in support of her claim that

Studies indicate that girls are motivated -- on a molecular and a neurological level -- to ease and even prevent social conflict. Maintaining the relationship at all costs is the female brain's goal. This may be especially true in the teenage female brain.

Yet only one of these studies has anything to do with social interaction at all -- and that's about the effect of estradiol in preventing cortisol suppression in subordinate female rhesus monkeys. There's nothing about girls' motivations (or anyone else's), the female brain's goals, the maintenance of relationships...

But I'm not going to complain again how Brizendine brandishes irrelevant journal articles like magical talismans to impress her audience. You can read my earlier posts on the subject, linked below, if you're not already completely sick of the topic. I took the time to follow up these references in order to underline Henig's point that if we're going to bring science to bear on public-policy questions -- from single-sex education to the number of female scientists or the role of women in public life -- everyone has to be able to look at the science that's cited.

In an open-access world, people writing books like Brizendine's would be expected to put their citations on line, with links, as I've done in this post and earlier ones, so that readers could evaluate the connection between their rhetoric and their references. This applies equally well to all the many other public-policy debates with scientific content: global warming, genetically-modified foods, early-childhood education, methods of teaching reading, and on through a long, long list.

[I read through those nine papers (well, eight papers and one abstract) rather quickly, so if you discover that I've mischaracterized any of them, please let me know.]

Previous posts on Louann Brizendine's The Female Brain:

"Neuroscience in the service of sexual stereotypes" (8/6/2006)
"Sex-linked lexical budgets" (8/6/2006)
"Sex and speaking rate" (8/7/2006)
"Yet another sex-n-wordcount sighting" (8/14/2006)
"The main job of the girl brain" (9/2/2006)
"The superior cunning of women" (9/2/2006)
"The laconic rapist in the womb" (9/4/2006)

And on the similar rhetorical practices in Leonard Sax's Why Gender Matters, and in Michael Gurian and Kathy Stevens' The Minds of Boys:

"David Brooks, cognitive neuroscientist" (6/12/2006)
"Are men emotional children?" (6/24/2005)
"Of rats and (wo)men" (8/19/2006)
"Leonard Sax on hearing" (8/22/2006)
"More on rats and men and women" (8/22/2006)
"The vast arctic tundra of the male brain" (9/6/2006)
"Girls and boys and classroom noise" (9/9/2006)

Posted by Mark Liberman at September 10, 2006 06:10 AM