July 2, 2005

The brains of women are neither better nor worse than those of men. However, they are measurably different.

THE INVITATION curled from her fax machine, a courtly question scrawled above the signature of a man whose name she did not recognize. “Would you be willing to collaborate with me on studying the brain of Albert Einstein?” It was signed Thomas Harvey.

Sandra Witelson did not hesitate. She wrote “yes” on the piece of paper and faxed it back. “It never occurred to me that it might be a joke,” she recalled. “I knew that Albert Einstein’s brain had been preserved and that it was somewhere where someone was looking after it.”

For 40 years, Harvey, a retired pathologist from Princeton, New Jersey, had been the quixotic custodian of the 20th century’s most famous brain. In 1955, he had conducted a routine autopsy of Einstein after the 76-year-old physicist died. The remains were to be cremated. Harvey, however, decided to preserve the organ responsible for the theory of relativity.

For Harvey more than morbid curiosity was at work. He believed that the slippery worms of Einstein’s brain tissue, pickled in warm formalin, embodied some clue to the mystery of intelligence. He held on to that hope through 40 years of indecision. Eventually, it led the soft-spoken Quaker to Witelson, a raven-haired Canadian psychologist. She had brains, dozens of them — the largest collection of normal brains in the world.

When Witelson had begun acquiring human brains, meanwhile, sex was the last thing on her mind. Inside her walk-in refrigerator at McMaster University in Ontario, her collection filled three walls of metal shelves. Each brain posed a riddle that had shaped her research for 30 years: How does the structure of the brain influence intelligence?

A professor of psychiatry and neuroscience, Witelson grappled with such a fundamental mystery by studying a somewhat smaller one: why certain abilities develop on one side of the brain rather than the other. The two hemispheres of the brain are almost symmetrical physically but can seem to be separate minds when it comes to awareness and mental processing. They even have different problem-solving styles, researchers report. Yet they work together seamlessly to produce a single mind.

By 1977, Witelson was trying to learn why language skills developed on the left side of the brain for all right-handers but on the right side for many left-handers. To compare the two sides, she needed normal brains — more than anyone had gathered before.

By 1987, 120 men and women had agreed to donate their brains after death. They all submitted to thorough psychological and intelligence tests so that each brain would be accompanied by a detailed profile of the mind that had animated it.

In an era when people probe the thought process with scanners, radioactive tracers and super-conducting sensors, Witelson’s approach was deliberately old-fashioned. She measured her brains. She weighed them. She cut them up and counted the cells. She traced synapses, the junctures where impulses pass from one neuron to another in the hidden root cellars of the brain. Wherever she looked, she discerned subtle patterns that only gender seemed to explain.

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.” No one knows how these neural differences between the sexes translate into thought and behaviour — whether they might influence the way men and women perceive reality, process information, form judgments and behave socially.

But even at this relatively early stage in exploration of the brain’s microanatomy, battle lines between scientists, equal rights activists and educators have been drawn. Some activists fear that research like Witelson’s could be used to justify discrimination based on gender differences, just as ill-conceived notions of human genetics once influenced laws codifying racial stereotypes about blacks and Asians.

Other experts argue that the physical differences Witelson observed may result not from the brain’s basic design but from conditioning that begins in infancy, when the brain produces neurons at a rate of half a million a minute and reaches out to make connections 2 million times a second. Spurred by learning, neurons and synapses are ruthlessly pruned, a process that continues in fits and starts throughout adolescence, then picks up again in middle age.

Witelson’s research helped establish that mental divide between the sexes is more complex and more rooted in the fundamental biology of the brain than many scientists once suspected. 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 grey 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 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.

Detailing differences

Witelson 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 analysed 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.

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 millimetres 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 per cent 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.

Witelson probed deeper, and eventually she formed a theory: The brains of men and women are indeed different from birth. Yet the differences are subtle. They might be found only among the synapses in brain structures responsible for specific cognitive abilities.

For so long, scientists had championed the idea of larger brains as an indicator of intellect. Witelson, however, gradually became convinced that overall brain size didn’t matter.

An odd pursuit

Researchers at the Moscow Brain Institute measured dozens of the most brilliant brains. Vladimir Lenin, the leader of Russia’s Soviet revolution, had a brain weighing about 3 pounds, they determined. The brain of writer Ivan Turgenev weighed 4.4 pounds. That of satirist Anatole France was 2.1 pounds.

At Princeton Hospital, Harvey weighed Einstein’s brain on a grocer’s scale. It was 2.7 pounds — less than the average adult male brain. He had the fragile organ infused with fixative and dissected it into 240 pieces, each containing about two teaspoons of cerebral tissue. He shaved off 1,000 hair-thin slivers to be mounted on microscope slides for study.

For years, Harvey agonized over how next to proceed. Then in 1995, Harvey happened across Witelson’s work. He read her research paper on gender differences and neuron density in the Journal of Neuroscience.

“It was impressive,” he recalled. He was even more intrigued to learn about her collection of brains. He was 84, still hoping that his tissue samples had something to teach about the neural geography of genius. To make ends meet, he was working in a plastics factory. Worrying about Einstein’s brain, like the years, had become a burden.

Harvey carefully packed it in the back of his battered Dodge and drove north to Witelson’s laboratory. “I had the brain in a big jar,” Harvey, now 94, recalled. At midnight, he crossed over the Rainbow Bridge by Niagara Falls into Canada.

Pieces fall into place

Witelson could barely contain her curiosity. Einstein’s brain — so far from ordinary in its intellectual achievement — might reveal a telltale anatomical signature. Size alone certainly could not account for his brain power. “Here was somebody who was clearly very clever; yet his overall brain size was average,” Witelson said. “It certainly tells you that, in a man, sheer overall brain size can’t be a crucial factor in brilliance.”

For a moment, she was like a schoolchild picking candies from a Valentine’s Day sampler. She judiciously selected 14 pieces of Einstein’s brain. She took parts of his right and left temporal lobes, and the right and left parietal lobes. Never had Harvey given away so much brain.

Witelson and her colleagues carefully compared the 40-year-old tissue samples with dozens of normal male and female brains in her collection. She also compared them with brains from eight elderly men to account for any changes due to Einstein’s age at the time of his death. She found that one portion of Einstein’s brain perhaps related to mathematical reasoning — the inferior parietal region — was 15 per cent wider than normal. Witelson also found that it lacked a fissure that normally runs along the length of the brain. The average human brain has two distinct parietal lobe compartments; Einstein’s had one.

Perhaps the synapses in this area were more densely interconnected. “Maybe this was one of the underlying factors in his brilliance,” she said. “Maybe that is how it works.” She took it as confirmation of her suspicions about the anatomy of intelligence. If there were differences affecting normal mental ability, they would show up in the arrangements of synapses at particular points in the brain.

Einstein, she was convinced, had been born with a one-in-a-billion brain. — Dawn/ALT-WP News Service (c) Los Angeles Times

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