Boys and girls are different…and not just in the obvious ways. Even their brains are wired differently–which has implications for everything from education to the treatment of mental disorders.
The differences between the male and female brain are the focus of a lengthy article by Larry Cahill, a neurobiologist at the University of California in Irvine, in the most recent Scientific American.
Cahill says scientists once believed that only the brain regions involved in mating behavior differed between males and females. But new technology for scanning brain activity (which I’ve written about before) is proving otherwise.
For example, Jill M. Goldstein of Harvard Medical School has found that parts of the frontal cortex (where many higher cognitive functions are centered) and parts of the limbic cortex (central to emotional responses) are bulkier (relative to the rest of the brain) in women, while parts of the parietal cortex (involved in space perception) and the amygdala (which responds to emotionally-arousing information) are bulkier in men.
Sandra Witelson at McMaster University has found that woman have a greater density of neurons in parts of the temporal lobe and frontal cortex associated with language comprehension and processing–which may explain women’s superior scores on tests of verbal fluency.
But since we rewire the brain as we use it, are these difference innate, or learned?
Probably the former. These same regions have the highest number of receptors for sex hormones during development. More directly, we know that even very young boys prefer “boy” toys like balls and cars, while girls gravitate to “girl” toys like dolls. Research by Melissa Hines of City University London and Gerianne M. Alexander of Texas A&M University has found the same preferences in young vervet monkeys–males prefer trucks, while females prefer dolls. It’s hard to argue that the monkeys learned those preferences from the surrounding culture.
Cahill suggests males prefer toys that can be “propelled through space and that promote rough-and-tumble play” because they relate to behaviors that help males hunt and secure a mate, while females gravitate toward toys that will help them build the skills necessary for some day nurturing young.
Researchers at the University of Cambridge, led by Simon Baron-Cohen, recently followed up on previous work that has shown that one-year-old girls spend more time looking at their mothers than one-year-old boys, and that one-year-old girls prefer films of faces to films featuring cars, while boys prefer the opposite. The Cambridge scientists put a video camera in a maternity ward and taped the reactions of one-day-old babies shown either the face of a live female student or a mobile that matched her face but scrambled her facial features. Even fresh out of the womb, they found, girls spent more time looking at the live face while boys spent more time looking at the mechanical one.
The differences seen in the amygdala between men and women are the focus of some of Cahill’s own research. He discovered that when men and women were shown a series of graphically violent films, the number of films they could recall weeks later depended on how active their amygdala was during the viewing (as revealed by a PET scan). But he also discovered, to his surprise, that in men only the right hemisphere of the amygdala lit up, while in women, only the left one did.
It’s long been held that the right hemisphere of the amygdala is mainly concerned with processing the central aspects of a situation, while the left processes the fine details. To test that, Cahill and his cohorts gave men and women a beta-blocker, propanolol, which dampens the activation of the amygdala, then showed them a disturbing slide show about a young boy run over by a car while walking with his mother. Sure enough, the drug made it harder for men to remember the gist of the story, while women remembered the gist, but had trouble remembering peripheral details. Additional studies have shown that differences in response occur immediately on viewing the material, before subjects have even had the time to consciously interpret what they’ve seen.
Another brain region that differs between men and women is the hippocampus, crucial to both memory storage and spatial mapping. It’s larger in women than in men–which may explain why men are likelier to navigate by “dead reckoning”–estimating distance in space and orientation–while women are more likely to navigate by monitoring landmarks.
Cahill’s Scientific American article lists much more research, all of which points to the same conclusion: boys and girls are different.
Didn’t I just say that?
