Friday, January 20, 2006

Oversimplifications: Language and the Brain

So a couple days ago at Washington Monthly, Kevin Drum linked to this TNR article about the growing disparity between female and male college performance, which slowly morphs into an article about the disparity between boys & girl's reading skills. There's some interesting stuff in it, and some things that need to be said, but this passage sort of irked me:

[Ken] Hilton conducted a series of studies, culminating in the summer of 2004 with a large survey of 21 school districts across New York state. Twelve were blue-collar and middle-class districts just like Rush-Henrietta. Another nine were among the wealthiest school districts in the state. Here is what Hilton found: In the first group, the blue-collar and middle-class schools, girls not only excelled in verbal skills but each year put a little more academic distance between themselves and the boys. Even in math, long thought to be a male stronghold, girls did better. But the real leap for girls was in reading. Another significant find: In these districts, the big hit boys take in reading happens in middle school, as they hit puberty. That's when a modest gap in verbal skills evident in elementary school doubles in size. As for the wealthy schools, more on them later.

Combine Hilton's local research with national neuroscience research, and you arrive at this: The brains of men and women are very different. Last spring, Scientific American summed up the best gender and brain research, including a study demonstrating that women have greater neuron density in the temporal lobe cortex, the region of the brain associated with verbal skills. Now we've reached the heart of the mystery. Girls have genetic advantages that make them better readers, especially early in life...

...Hilton's research on the wealthiest schools is revealing. Girls still do better in verbal skills in those districts. But Hilton discovered an important distinction. When the wealthy boys enter middle school, they don't lose ground. And that holds steady through high school.
(emphasis mine)

Now, there's a bit that I'm uncomforable with here. But I'm going to issue some disclaimers, because there's probably going to be some foot-in-mouth action going on here shortly:
1. I have not read the Scientific American article referred to, nor am I intimately familiar with the research on which it's based.
2. I am also not intimately familiar with a lot of the published material on gender differences in the brain.
3. None of this prevents me from having an opinion, so just take everything I say from here on with a pinch of salt.

First off, let's just make clear that when we're talking about the temporal lobe, we're talking about a lot more than just reading skills here. The Wikipedia entry provides a good starter list of activities implicated in this general area: hearing--especially auditory processing--being primary, and recognition of complex visual stimuli are two of the heavy-hitters. But also of note are the hippocampus--key to memory and navigation--and the amygdala--key to the fear and stress responses, but also to emotions in general--both of which are temporal lobe structures. So if you wanted to make an argument that more dense wiring of the temporal lobe leads to greater reading skills, I'd really have to see an accompanying argument that it also leads to enhanced function in the rest of the activities implicated.

I should point out that the structure he's probably referring to is Wernicke's Area, which is key to language comprehension, and is found (generally but not always) at the junction of the temporal and parietal lobes. But the interesting thing here is that different parts of the brain seem to be responsible for language comprehension and language production, the latter of which seems to occur in Broca's area. I should throw out the caveat here that the distinctions we're going to refer to are incredibly simplified for purposes of explanation.

Now, unfortunately I can't seem to find the notes from the semester in which I covered this (I wouldn't dare to use the phrase "thrown away" without further investigations), but as I recall it, one of the really neat things ("neat" here means "morbidly fascinating to neuroscientists") about this distinction is that damage to each area produces a different variety of aphasia. Wernicke's aphasia is characterized by an ability to form normal sounding sentences with accurate syntax, that are overly verbose and frequently feature word replacement and repetition, leading to sentences that sound right but don't actually make any sense. Again, I can't find my notes so I'll just throw out Wikipedia's example because it's there:

I called my mother on the television and did not understand the door. It was too breakfast, but they came from far to near. My mother is not too old for me to be young.

Also of note is the fact that patients who have recovered from this type of aphasia consistently report a lack of comprehension of sentences that were spoken to them, and a similar lack of comprehension of their own speech.

Broca's aphasia, by contrast, basically results in a labored list of key words. Wiki's example:

"Yes... ah... Monday... er... Dad and Peter H... (his own name), and Dad.... er... hospital... and ah... Wednesday... Wednesday, nine o'clock... and oh... Thursday... ten o'clock, ah doctors... two... an' doctors... and er... teeth... yah."

Patients report a retention of comprehension ability, and recovered patients describe the experience as knowing what they wanted to say, but being unable to do so.

I may have derailed the train a bit at this point, but the point of all this is that the article seems to be trying to discuss not only differences in reading comprehension, but also differences in writing ability as well as other distinctions. Now, comprehension occurs in Wernicke's area, located in the temporal lobe. But Broca's, involved in expression, is located in the frontal lobe.

The argument that someone reading this has already developed in their mind at this point is, "But isn't it possible that Broca's area--or the frontal lobe in general--is also more densely wired in female brains?"

The answer to that is, I'd be willing to put good money down that such is the case.

Human brains are sexually dimorphic. As I understand it (and I could be wrong), the dimorphism is two-fold: the brains of males are larger, and contain a greater number of neurons. The brains of females, although smaller and containing fewer neurons, are much more densely wired. So what does this mean? Is bigger better, or is less more? This is something we're just starting to get a handle on, but the likely answer is that such a binary response is far too simplistic. For instance, keep in mind that there are also relative dimorphisms at work. One structure may be relatively larger in one gender than another, or may be more relatively densely wired, or an activity may even be controlled by a slightly different part of the brain. These things do happen.

So unless I'm totally barking up the wrong tree, saying "women have greater neuron density in the temporal lobe cortex" sounds to me a lot like saying "women have different reproductive machinery than men." If I'm totally wrong here, please let me know so I know when to start feeling like an idiot.

I had a bit more to say about this article here, but I think I'll leave it standing like I wisely utilized a single paragraph as inspiration for a lecture on language and the brain. That said, I leave you with this final quote that made me smile:

But, as Welsh pointed out, even these underperforming boys nearly always landed a spot in some college. That's due to one of the best-kept secrets in college admissions today: the affirmative action campaign to recruit men. Most admissions directors sifting through stacks of applications from men and women can only sigh at the contrast. The average male applicant has far lower grades, writes a sloppy essay, and sports few impressive extracurriculars. Those admissions directors face a choice: Either admit less-qualified men or see the campus gender balance slip below 40 percent male, a point at which female applicants begin to look elsewhere.

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