differenceblog, posts by tag: asymmetry - LiveJournal

How much of our brain's gender is visible in our hands? Sanders and Waters (2001) found that performance on sexually dimorphic tasks was predicted not by sex, but by finger ridge count (dermatoglyphics). Most people have more ridges on their right fingertips than their left. "Male-favouring" tasks were better performed by people with more right ridges. "Female-favouring" tasks were better performed with more on their left fingers. Kimura and Carson (1993) found that the left-asymmetry was more prevalent in women and homosexual men than in the general population. Mustanski et al (2002) (with everyone's favorite "sex expert" J. Michael Bailey contributing) found that left-handedness was more prevalent in homosexual women than heterosexual women, but not in homosexual men versus heterosexual men. Mustanski found no association between dermatoglyphic asymmetry and sexual orientation. Williams et al (2000) is one of many sources to report a sexual dimorphism in finger length ratios that may reflect sexual orientation as well (see also: Rahman and Wilson, 2003, Brown et al (2002)).

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Are you looking at your hands yet? In my previous life, I read palms a little. I even volunteered as a palm reader in a charity carnival in junior high. At that point, I was taking my cues largely from the patterns I learned from my mother and from books on palmistry. After college, I still read palms -- but at that point I was trading the readings for free drinks. I also learned to do the readings more as a "warm read" -- taking cues from people's reactions more than from anything I saw on their hands.

Adult women seem to have more white matter than men (see "Does Size Matter", 11/1/06), a finding that is popularly used to explain gender differences in cognitive processes. Diffusion tensor imaging (DTI) is a MRI technique that is being used to examine white matter connectivity, and as such, may have extensive applications in studying sex differences.

Silveri et al (2006) used DTI to assess differences in the white matter connectivity of adolescents, in an examination of impulse control and response inhibition: "sex-specific differences were observed for the relationship between FA [essentially, preferentiality of flow-direction] and impulsive behavior in the right anterior callosum for males and in the splenium for females." Szeszko et al (2003) found greater leftward asymmetry in the frontal lobe in women vs. men using DTI, correlating with verbal IQ. This is especially confusing in light of prior findings indicating greater asymmetry in men's language localization (see Speak My Languge, 1/19/07).

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I'm always slightly peeved by the "women have more white matter" arguments because they tend to set off my "wonk science" alarm. It always feels like it's just another justification to call women irrational and men logical. The really annoying part is that I can be aware of myself not giving the argument enough of a chance for completely irrational reasons, which makes it feel like the argument is legitimate. After all, my brain (probably) developed normally for a female, and therefore I'm doomed to irrationality and diffuse inference, right? Some days it feels like I don't need television; I can just sit back and watch my biases chase their own tails.

Men and women are often said to "speak a different language." The primary explanations given for this tend to be sociological, such as Cheris Kramarae's "muted group theory." However, some anatomical theories of sex differences in language are emerging.

Shaywitz et al (1995) suggest that men's brains have greater language lateralization than women's; that is, language is almost entirely localized to the left hemisphere in men, but represented on both sides in women. Miller et al (2005) found right-hemisphere or bilateral language representation more often in women than men in a group of 170 survivors of early brain injury, which they suggest may indicate greater adaptability in female brains. However, this result doesn't seem to take into account the greater prevalence of bilateral representation in women in general. On the other hand, supporting the idea that women's brains may have an easier time preserving language function, Walder et al (2006) male schizophrenics suffered deeper language impairment than female schizophrenics, when compared to healthy controls.

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In 1995, I broke a bone for the first time; it was my skull. It's the only bone I've ever broken, and it was a hairline fracture in my forehead over my right eye. It was the summer before my third year of college, which was when I was due to take the major writing requirement course for my degree. That fall, I found I had a much harder time concentrating and putting ideas into words than I'd ever had before. I ended up writing my professor a letter asking for help, because I blamed my difficulty on the head injury that summer. I needn't have worried, but at the time, I ended up very stressed out worrying about how much I'd impaired myself with my car accident. I passed the course without trouble, and in retrospect, it seems more likely that stress was the culprit, rather than trauma, but at the time, I was scared as hell that I'd killed my ability to write.