September 17, 2007

How big is your crockus?

Yesterday afternoon, Heidi W. wrote to say:

Thought you might be interested in knowing that Dan Hodgins is the brain-sex guru who's been making the rounds in Early Childhood Education (ECE). Earlier this year, my (very large urban) school district invited him to speak on, "What About Those Boys?", and I just learned that they asked him to come back this fall to speak about discipline. A Google search indicated that he's been speaking at a lot of regional and national ECE conferences.

Ms. W. provided a link to copies of Prof. Hodgins' handouts, from a site where he gave a talk in 2003, and observed that

It seems that, around here, I'm in the minority in feeling very alarmed by his claims, which are supposedly supported by brain research. Red flags went up for me when, very early in his presentation, he showed a drawing of the brain and claimed that, "Girls see the details of experiences... Boys see the whole but not the details".

On that drawing of the brain, the motor strip was highlighted, as well as a much smaller area just anterior to it, which he called the "crockus". Ostensibly, he was supporting the 'girls seeing details' assertion when he claimed, "The crockus is four times larger than in boys" (as if the highlighted motor strip was "the crockus" in girls). I've searched extensively but have been unable to find any information about an area of the brain called the crockus --are you familiar with this term?

I'm puzzled too. A "smaller area just anterior to the motor strip" that shares some sounds with "crockus" would be Broca's area, which is functionally implicated in speech -- but Heidi is "ABD in Ed Psyc, with a cognate in Neuropsyc", and so she's unlikely to have mis-heard "Broca's" as "crockus". [Update: she informs me that "the word crockus was spelled out as such in the handout that Hodgins gave to us, and I was quoting directly from that handout in my message to you. It was definitely not Broca's area to which he was referring."] In any case, I've never heard that Broca's area is larger in girls, much less four times larger. In fact, I don't think there are any human brain areas at all where a reputable claim for a factor-of-four size difference by sex has ever been made. (If you think you know what brain area Dan Hodgins meant by "crockus", please tell me...)

In the Mott Community College Focus, I found two articles by Hodgins, ("Male and Female Differences" and "Classroom Climate that support Male and Female Differences"). They say nothing about the "crockus" or any other brain structures differing in size by a factor of four, but they do contain a number of specific factual claims about brain sex. For example, Hodgins tells us that

In most cases, female brains mature earlier than males. An example is in the myelination of the brain. One of the last steps in the brain’s growth to adulthood occurs as the nerves that spiral around the shaft of other nerves of the brain, like vines around a tree, are coated. This coating is myelin, which allows electrical impulses to travel down a nerve fast and efficiently. Myelination continues in all brains into the early twenties, but in young women it is complete earlier than in young men, almost twelve – eighteen months earlier

There's some suggestion of confusion about the nature of myelin here, in the talk about "the nerves that spiral around the shaft of other nerves", but never mind that. Do female brains really mature earlier than males, specifically with respect to myelination?

Hodgins doesn't cite any sources, but as far as I can tell, his assertion is contradicted by the published literature -- and this is an area where there's been a lot of recent publication, because MRI's ability to separate gray and white matter has made in vivo studies possible. In the first place, it seems that myelination continues in humans well beyond "the early twenties". According to Elizabeth R. Sowell et al., "Mapping cortical change across the human life span", Nature Neuroscience 6:309-315, 2003,

Post mortem studies have shown that myelination continues into a person's 30s and perhaps beyond, which could explain the increase in cerebral white matter observed into adulthood in the volumetric imaging studies. [...]

The increase in white matter volume peaked at age 43 and declined thereafter.

Specific information about human sex differences in the development of cerebral gray matter and white matter volume was presented in M.D. De Bellis et al., "Sex Differences in Brain Maturation during Childhood and Adolescence", Cerebral Cortex 11(6): 552-557, 2001. They studied 61 males and 57 females ranging in age from 6.9 to 17 years.

[F]indings from cross-sectional studies suggest that cerebral white matter (WM) volume and the area of the corpus callosum (CC), the main interhemispheric commissure, increase significantly from childhood through late adolescence. Recent results from longitudinal MRI studies of healthy children and adolescents have confirmed these age-related linear increases in cerebral WM and CC area. These observations may reflect in vivo evidence of age-related progressive events such as axonal growth and myelination. [...]

We investigated the relationship between age, sex and cerebral [gray matter] GM and WM volumes and CC area using high-resolution MRI volumetric analyses in a large community sample of healthy, age-matched and sociodemographically similar male and female children and adolescents. We specifically investigated age- related sex differences in human brain maturational processes (age-related changes in cerebral GM and WM volumes and CC area). [...]


Males had larger intracranial and cerebral volumes than females by 11 and 12%, respectively. These effects remained after correction for height. Cerebral GM and WM volumes and CC areas did not differ between gender groups after adjustment for cerebral volumes.

What about sex differences in maturation rate, i.e. age-by-sex interactions?

The sex by age interaction term was significant for cerebral GM and WM volumes and CC area. The slopes of these changes significantly differed between male and female subjects. Thus girls showed significant developmental changes with age but at a slower rate than boys. Specifically, males had an ~19.1% reduction in GM volume between 6 and 18 years of age compared with a 4.7% reduction in females. On the other hand, males had a 45.1% increase in WM and a 58.5% increase in CC area compared with 17.1 and 27.4% increases, respectively, in females.

Here are the plots of the relevant age-by-sex results:

Figure 1. Scatterplots of cerebral volume (A), cerebral GM (B) and cerebral WM (C) volumes and CC areas (D) by age and sex in healthy male (n = 61) (solid lines, individual points = Y) and female (n = 57) (dashed lines, individual points = X) children and adolescents. Cerebral GM and WM volume and CC area means were adjusted for cerebral volume.

In other words, the age-related effects in brain development (as measured in this study) went in the same direction in 7-to-17-year-olds of both sexes, but at a faster rate in boys. (And as usual, the distributions for males and females are so highly overlapped that it seems irresponsible to draw any general conclusions about "classroom climates" for sex-specific education.)

I have no idea whether all this means anything about learning styles or appropriate educational practice; but it does suggest that Prof. Hodgins (who gives no references) is talking through his crockus.

Heidi W.'s note discussed various of Hodgins' other claims, such as the one about boys' brains going into "pause states", so that boys (as opposed to girls) need frequent "pause breakers" such as "spinning, shouting and jumping". I've come to the end of my breakfast hour, so most of that stuff will have to wait for another time. But I can't resist a quick note about another of Hodgins' brain-sex assertions, one that is more specifically related to speech and language:

Another structural difference, and perhaps the most striking, is the corpus callosum, the bundle of nerves that connects emotion and cognition. In females, it is up to 20% larger than in males, giving females better decision making and sensory processing skills. All learning must connect emotion and cognition. Because of this difference in size, females have better verbal abilities and rely heavily on verbal communication; males tend to rely heavily on nonverbal communication and are less likely to verbalize feelings. The current research suggests that sixty-seven per cent of males throughout their life are visual learners. This learning style has immense ramifications in our present culture, which relies so heavily on talk, conversation, words.

In the first place, what the corpus callosum connects is the right and left hemispheres of the cerebral cortex, not "emotion and cognition". In normal humans of both sexes, both the right and left sides of the brain are involved in both cognitive and emotional processing. As for the relative size of the corpus callosum in males and females, we just saw De Bellis et al. assert that in their sample, "CC areas did not differ between gender groups after adjustment for cerebral volumes". (Before adjustment for overall brain volume, they found an average male CC volume of 8.04 cc vs. 7.69 cc for the females in their study.)

A few weeks ago ("And why 'without sauce'?", 8/19/2007), I quoted from K.M. Bishop and D. Wahlsten, "Sex Differences in the Human Corpus Callosum: Myth or Reality?", Neuroscience & Biobehavioral Reviews, 21(5) 581-601, 1997:

It has been claimed that the human corpus callosum shows sex differences, and in particular that the splenium (the posterior portion) is larger in women than in men. Data collected before 1910 from cadavers indicate that, on average, males have larger brains than females and that the average size of their corpus callosum is larger. A meta-analysis of 49 studies published since 1980 reveals no significant sex difference in the size or shape of the splenium of the corpus callosum, whether or not an appropriate adjustment is made for brain size using analysis of covariance or linear regression. It is argued that a simple ratio of corpus callosum size to whole brain size is not an appropriate way to analyse the data and can create a false impression of a sex difference in the corpus callosum. The recent studies, most of which used magnetic resonance imaging (MRI), confirm the earlier findings of larger average brain size and overall corpus callosum size for males. The widespread belief that women have a larger splenium than men and consequently think differently is untenable. Causes of and means to avoid such a false impression in future research are discussed.

Heidi ended her note this way:

So the ECE folks here (of which I'm one) saw this dog and pony show by Hodgins and they just ate it up (I had to walk out). I found your Language Log when I was trying to locate info about [some other research that Hodgins referred to]. Any thoughts?

I think it's disturbing that such easily-refuted nonsense is so easily and widely accepted. We've got serious educational problems to solve, and sex differences -- whether genetic or cultural -- are clearly part of the picture. But surely no one's interests are served by promoting solutions on the basis of pseudo-scientific bafflegab.

Those males (and females) among us whose "brains go into pause after too much talking", as Prof. Hodgins puts it, might feel the need for a comic-strip break at this point. This morning's Dilbert will fit right in:

Prof. Hodgins' work certainly renews my appreciation for science. In fact, it makes me want to jump, spin and shout!

[Note: Besides decoding that "crockus", here's another puzzle that Language Log readers may be able to help me with. In Prof. Hodgins' article on "Male and Female Differences" he writes:

This information is an accumulation of research, study and observation over the last ten years that I had the opportunity to conduct with Dr. Gerison and Dr. Stake from the University of Southern California.

I couldn't find anyone named "Gerison" or "Stake" in the current USC online directory. Nor could I turn up any plausible "Gerison" in a Google search (and "stake" occurs too often as an ordinary noun to be a useful search term, and {author:gerison author:stake} comes up empty in Google Scholar, and I'm out of time and here, in that order). If you think you know who these researchers are, please tell me. ]

[Update -- readers have provided many suggestions and clues. They range from plausible if unsatisfactory (e.g. there is a Dr. Jayne E. Stake who works on "issues related to the self-concept and empowerment of women", but she's at the University of Missouri), not USC, and she hasn't done neuroscience research) to, well, less serious ("Gerison Stake" is an anagram for "searing tokes"). So far, Drs. Gerison and Stake remain as mysterious as the elusive Crockus.]

Posted by Mark Liberman at September 17, 2007 06:53 AM