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 May 14, 2005
Battle of the Sexes a Matter of Perception
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By E.J. Mundell, HealthDay Reporter

MONDAY, Feb. 28 (HealthDay News) -- Are men better than women when it comes to certain intellectual tasks, such as remembering the location of objects?

While debate rages, 112 monkeys (and a few scientists) have been hard at work puzzling it out.

Researchers report that, when challenged by a kind of food-baited shell game, young male monkeys outperformed females at correctly remembering the location of the prize.

But with just a minimum of training, that intellectual gender gap closed completely.

That suggests that any gender-based differences in intellect -- whether simian or human -- "are plastic, they aren't rigid. You can develop these skills," said lead researcher Agnes Lacreuse, a professor of neuroscience at the Yerkes National Primate Research Center in Atlanta.

According to Lacreuse, the study results echo similar findings in humans when it comes to gender-based differences in what neuroscientists call "spatial cognition" -- the ability to visualize, remember and manipulate objects in three-dimensional space.

Not everyone agrees the monkey study is a good fit for Homo sapiens, however.

"The problem is that spatial memory covers a wide area -- there are a lot of spatial tasks that don't show a sex difference at all [in humans], or even show a slight female advantage," said Temple University's Nora Newcombe, an expert in gender-based cognitive differences.

She believes Lacreuse's findings may say a lot about the minds of rhesus monkeys, but less about the human kind.

Up until now, the scientific literature on various 'intellectual gender gaps' has been contradictory, with some studies suggesting that men are better at spatial tasks while women excel at verbal skills. And yet, even within those categories, scientists agree there's often no clear pattern that favors one gender over the other.

Lacreuse said a key problem for researchers has been that humans are profoundly influenced by upbringing and environment. That's made it tough for scientists to rule out confounding factors that could bias test results.

"But with monkeys, we have much more control," she explained.

"Their environment is the same, they all eat the same things, they don't take medications," she added. "So we don't have to worry about all that. When you work with humans, on the other hand, they are each so different."

Another advantage of working with the rhesus monkey is that its brain, while smaller, still "has a basic function and anatomy" similar to the human brain, Lacreuse said.

In her team's first set of experiments, 90 adult monkeys of varying ages were presented with a table dotted with 18 food wells. Food was hidden in select wells under one or more brown lids, and the monkey pushed away the lids until he or she found the food. After each task, a screen would drop down, keeping the table out of the monkey's line of sight for about 10 seconds. Once the screen was raised again, the monkey quickly went to work, searching its spatial memory to recall the correct location of the food.

Reporting in the February issue of Behavioral Neuroscience, the researchers say they saw one big difference among the younger primates.

"Young males were much better than the young females at the spatial tasks," Lacreuse said.

However, that male advantage faded with age, so that "by the time we compared the older monkeys, there is no longer a sex difference," she said.

According to the Atlanta researcher, that finding strengthens the idea that testosterone may somehow enhance spatial memory in males.

"We know that in humans, testosterone levels decline progressively at around 50 years old," she said. "And testosterone is linked to spatial abilities in humans. We suspect the same thing happens in monkeys with age."

A second experiment suggests that, even when monkeys are young, any intellectual divide between the two genders is easily bridged.

In that experiment, the researchers provided 22 young monkeys with very simple training to help improve their success in the "shell game."

Although young males didn't appear to benefit from the training, young females quickly improved until they matched young males in remembering and retrieving the hidden food -- effectively closing the gender gap.

So, what does all this mean for humans?

According to Newcombe, the findings are interesting, but far from conclusive. With humans, even in the field of spatial cognition, neither gender is the clear winner, she said.

In fact, a similar study involving humans -- in which researchers arranged objects on a table and then asked men and women to identify their locations from memory -- ended in "the women showing an advantage," Newcombe said.

In other spatial tasks -- such as accurately picturing objects upside down -- men tend to come out ahead.

Newcombe believes the Atlanta findings may therefore be "species-specific."

Even the finding that suggests the gender gap closes easily after training isn't easily replicated in the human world, she said.

With spatial memory skills, "there have been some studies that have claimed to have that kind of an effect -- that you see improvement -- but both men and women get better," so the overall gap still remains, Newcombe said.

What was "really welcome" about the Atlanta study was that the researchers did take the time to focus on the value of training, Newcombe said.

"A lot of times researchers will just interpret any kind of sex difference as evidence for a rigid, biological difference," she said. "This study really does tend to argue that the difference is biologically set, perhaps, but that it's also really easy to change if you work on it."

More information

For more on what monkeys bring to human science, check out other advances at the Yerkes National Primate Research Center (www.yerkes.emory.edu ).

SOURCES: Agnes Lacreuse, Ph.D., assistant research professor, division of neuroscience, Yerkes National Primate Research Center, Emory University, Atlanta; Nora Newcombe, Ph.D., professor, psychology, Temple University, Philadelphia; February 2005 Behavioral Neuroscience

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