Sizing Up The Sexes

Scientists are discovering that gender differences have as much to do with the biology of the brain as with the way we are raised

  • Share
  • Read Later

(5 of 7)

Encouraged by the discovery of such structural differences, many researchers have begun looking for dichotomies of function as well. At the Bowman Gray Medical School in Winston-Salem, N.C., Cecile Naylor has determined that men and women enlist widely varying parts of their brain when asked to spell words. By monitoring increases in blood flow, the neuropsychologist found that women use both sides of their head when spelling while men use primarily their left side. Because the area activated on the right side is used in understanding emotions, the women apparently tap a wider range of experience for their task. Intriguingly, the effect occurred only with spelling and not during a memory test.

Researchers speculate that the greater communication between the two sides | of the brain could impair a woman's performance of certain highly specialized visual-spatial tasks. For example, the ability to tell directions on a map without physically having to rotate it appears stronger in those individuals whose brains restrict the process to the right hemisphere. Any crosstalk between the two sides apparently distracts the brain from its job. Sure enough, several studies have shown that this mental-rotation skill is indeed more tightly focused in men's brains than in women's.

But how did it get to be that way? So far, none of the gender scientists have figured out whether nature or nurture is more important. "Nothing is ever equal, even in the beginning," observes Janice Juraska, a biopsychologist at the University of Illinois at Urbana-Champaign. She points out, for instance, that mother rats lick their male offspring more frequently than they do their daughters. However, Juraska has demonstrated that it is possible to reverse some inequities by manipulating environmental factors. Female rats have fewer nerve connections than males into the hippocampus, a brain region associated with spatial relations and memory. But when Juraska "enriched" the cages of the females with stimulating toys, the females developed more of these neuronal connections. "Hormones do affect things -- it's crazy to deny that," says the researcher. "But there's no telling which way sex differences might go if we completely changed the environment." For humans, educational enrichment could perhaps enhance a woman's ability to work in three dimensions and a man's ability to interpret emotions. Says Juraska: "There's nothing about human brains that is so stuck that a different way of doing things couldn't change it enormously."

Nowhere is this complex interaction between nature and nurture more apparent than in the unique human abilities of speaking, reading and writing. No one is born knowing French, for example; it must be learned, changing the brain forever. Even so, language skills are linked to specific cerebral centers. In a remarkable series of experiments, neurosurgeon George Ojemann of the University of Washington has produced scores of detailed maps of people's individual language centers.

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6
  7. 7