Sunday, June 19, 2005

Deep, Dark Secrets of His and Her Brains - Yahoo! News

Deep, Dark Secrets of His and Her Brains - Yahoo! News: "Wherever she looked, she discerned subtle patterns that only gender seemed to explain.

'We actually didn't set out to find sex differences,' she said. 'Sometimes as a scientist, you are doing one thing and you bump into something else.'

Controversial Matters

The brains in Witelson's freezer are contested terrain in a controversy over gender equality and mental performance.

Her findings — published in Science, the
New England Journal of Medicine, the Lancet and other peer-reviewed journals — buttress the proposition that basic mental differences between men and women stem in part from physical differences in the brain.

Witelson is convinced that gender shapes the anatomy of male and female brains in separate but equal ways beginning at birth.

On average, she said, the brains of women and men are neither better nor worse, but they are measurably different.

Men's brains, for instance, are typically bigger — but on the whole, no smarter.

'What is astonishing to me,' Witelson said, 'is that it is so obvious that there are sex differences in the brain and these are likely to be translated into some cognitive differences, because the brain helps us think and feel and move and act.

'Yet there is a large segment of the population that wants to pretend this is not true.'"

[...]

In the last decade, studies of perception, cognition, memory and neural function have found apparent gender differences that often buck conventional prejudices.

Women's brains, for instance, seem to be faster and more efficient than men's.

All in all, men appear to have more gray matter, made up of active neurons, and women more of the white matter responsible for communication between different areas of the brain.

Overall, women's brains seem to be more complexly corrugated, suggesting that more complicated neural structures lie within, researchers at UCLA found in August.

Men and women appear to use different parts of the brain to encode memories, sense emotions, recognize faces, solve certain problems and make decisions. Indeed, when men and women of similar intelligence and aptitude perform equally well, their brains appear to go about it differently, as if nature had separate blueprints, researchers at UC Irvine reported this year.

"If you find that men and women have fundamentally different brain architectures while still accomplishing the same things," said neuroscientist Richard Haier, who conducted the study, "this challenges the assumption that all human brains are fundamentally the same."

Yet, for the most part, scientists have been unable to document such patterns conclusively.

No one, however, had scrutinized as many brains as Witelson.

Detailing Differences

She began by studying the corpus callosum, the cable of nerves that channels all communication and cooperation between the brain's two hemispheres.

Examining tissue samples through a microscope, she discovered that the more left-handed a person was, the bigger the corpus callosum.

To her surprise, however, she found that this held true only for men. Among women there was no difference between right-handers and left-handers.

"Once you find this one difference," she remembered thinking, "it implies that there will be a cascade of differences."

As she systematically analyzed the brains in her refrigerator, she discovered that other neural structures seemed larger or smaller among men, depending on whether the man had been right-handed or left-handed.

They were relatively the same size in women. "The relationships that we were finding were always — and I do mean always — different for men and women," she said.

She narrowed her study to right-handed men and women, still looking for differences in microscopic anatomy between the left side of the brain and the right side. She meticulously counted the neurons in sets of tissue in which each sample measured 280 microns wide — about twice the thickness of a human hair — and 3 millimeters deep.

Staring through the microscope, she was baffled.

"I had the first two patients, and they were so very different," Witelson said. "I kept looking and looking at them, trying to see what the difference could be."

Then she consulted the donor documentation for each tissue sample. "Finally, I saw that one was a man, and one was a woman."

Among women, the neurons in the cortex were closer together. There were as many as 12% more neurons in the female brain.

That might explain how women could demonstrate the same levels of intelligence as men despite the difference in brain size.

"So among female brains, the cortex is constructed differently, with neurons packed more closely together," she said.

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