Is it true, as the old nursery rhyme claims, that little girls are made of "sugar and spice and everything nice," and little boys are made of "slugs and snails and puppy dog tails?"
Well, not exactly, but it may not be entirely wrong, either.
Researchers at the University of Pennsylvania School of Medicine say they have evidence that shows there is a physiological reason for why men are more aggressive than women. Men tend to be more hot headed than women, the researchers suggest, because our brains are fundamentally different.
In a nutshell, the research indicates that men are more aggressive than women because the part of the brain that modulates aggression is smaller in men than it is in women. Both genders have about the same ability to produce emotions, but when it comes to keeping those emotions in check, men have been shortchanged.
Battling Brain Parts
The research is part of an ongoing effort by a husband and wife team who are using the latest tools of their trade to peer inside the human brain and see what's really going on. Psychologist Ruben C. Gur, director of Penn's Brain Behavior Laboratory, and psychiatrist Raquel E. Gur have completed several research projects showing that a sizeable portion of human behavior can be laid directly at the doorstep of neurological differences in the brain, especially between the two genders.
They have shown, for example, that just because men have bigger heads than women, they aren't smarter. Women's brains are smaller, but they have a higher processing capacity, thus offsetting the difference.
For their latest project, published in a recent issue of the Journal of the Cerebral Cortex, the Gurs made use of past research that shows that different areas of the brain are responsible for different functions. The region at the base of the brain includes the amygdala, which is involved in emotional arousal and excitement. A frontal area around the eyes, called the "orbital frontal cortex," is involved in the modulation of aggression.
The amygdala makes it possible for us to get stirred up while the orbital region tries to keep us in check.
So if you're deeply insulted by the tone of this article, the amygdala section of your brain might say "kill the writer."
But fortunately, the "orbital frontal area might say, 'well, you are angry, but killing may not be such a great idea, there can be consequences, so how about if you just say I am angry,"' explains Ruben Gur.
Scientists have understood for a number of years now that the frontal region plays modulator in an emotionally charged situation, because damage to that part of the brain can leave a person unable to keep his or her temper under control.
"I've known several cases where fairly regular people ended up on death row because they started doing some very bad things after a head injury," Gur says.
Woman With a Temper
The researchers, who included Faith Gunning-Dixon and Warren B. Bilker of Penn's Department of Epidemiology, wanted to take it a step farther. They wanted to see if there was a significant difference between men and women in the size of the orbital frontal cortex ( call it the "modulator") and the amygdala (call it the "emotional stimulator.")
They took 116 healthy adults (57 men and 59 women) and scanned each of their brains with a magnetic resonance imaging device. They then used those brain scans to measure the ratio between the orbital frontal cortex and the amygdala of each participant.
The result, Gur says, is very compelling.
They found that the women had a significantly higher volume of orbital frontal cortex than the men, although the amygdala remained about the same. What that suggests is that when anger is aroused, women are better equipped neurologically to step on the brakes than men.
In fact, only one man had a "modulator" that was at least seven times larger than his "emotional stimulator," compared to eight women, and only three women had a really small modulator (less than 3.5 times the size of the stimulator) compared to about a quarter of the men.
But oddly enough, one woman had the smallest modulator of all, less than two times the size of her amygdala, suggesting that it might not be a good idea to rile her up. But that can't be said for sure, because no effort has been made yet to determine if the subjects in the study really were as mellow, or violent, as the ratio of their modulator to their stimulator would suggest. That may come next, because Gur is intrigued by the woman with the dinky modulator.
"I would really like to get to know her," he says.
Takes All Kinds
Although this research, like several previous projects, indicates that (could we have a drum roll here?) there are fundamental differences between men and women, Gur says it doesn't mean that one gender is superior to the other.
Even aggression has its place.
"We do need men who can express aggression when it's appropriate," he says. "Otherwise there will be some bad people out there who will do us harm."
But it's equally important to be able to keep aggression under control, and the researchers believe this work may point the way to better clinical treatment for persons with serious aggressive tendencies.
It may be possible, for example, to come up with drugs that will stimulate the "modulator," making it more effective in controlling the rage boiling out of an emotional encounter.
At the very least, it might help some persons deal more effectively with gender differences because it shows that we aren't just the sum total of our cultural experiences. Some of us may really be made of "slugs and snails and puppy dog tails."
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.