It is snowing in the cartoon, and two birds are perched on a branch looking at a kid directly below them who is trying to catch one of the big white flakes on his tongue. His mouth is open so wide his tonsils are a bulls-eye in the centre of his face. "Hey," one bird says to the other. "Are you thinking what I'm thinking?"
When women process cartoons like this one they use more parts of their brain than men, a new study has found. But if reading the comics page is more work for women, it also may be more fun.
The experiment found that the reward centre of the brain -- the part that is activated when people, for instance, win at gambling or snort crack cocaine -- is more active in women than men when they get the joke that a cartoon delivers.
"Women appeared to have less expectation of a reward, which in this case was the punchline of the cartoon," says Allan Reiss, a professor of psychiatry and behavioural science at Stanford University in California. (The birds are planning to plop their own sticky white stuff into the boy's mouth.)
The experiment is the first to use brain-imaging to compare how women and men understand humour. It builds on earlier work that found important differences in what makes men and women laugh.
In general, men prefer jokes or slapstick comedy, while women like funny stories or anecdotes, says Rod Martin, a psychology professor at the University of Western Ontario.
There are also important differences in why men and women use humour when dealing with others. Men are far more likely to slag each other, and to use "hostile" humour to establish dominance, says Dr. Martin, who has spent 25 years studying humour.
"It reminds me a little of wrestling. You try to pin the other guy, then he tries to pin you."
Women, on the other hand, are more likely to be funny in order to build and maintain relationships and make others more comfortable.
Those gender differences emerge early. Daniela O'Neill, a researcher at the University of Waterloo who studies how children learn and use language, has noticed that even as toddlers, boys are more likely that girls to initiate conversations using knock-knock jokes.
Knock-knock jokes aside, there are also many similarities between males and females when it comes to humour, Dr. Martin says. Men and women are equally creative when they try to be funny. Both can laugh at themselves. Both enjoy sexual humour.
Dr. Martin is now investigating how couples use humour, and how that relates to how satisfied they are with their relationships. He videotaped 50 couples who discussed a problem. After a few minutes, they seemed to forget the camera was there, he says.
He is still analyzing the content of those conversations, but says both men and women used humour to get their points across. Sometimes it was positive, and used to deflect conflict or display a sense of commitment. But sometimes it got nasty and involved aggressive putdowns. He said he wondered why some of the couples stayed together.
The brain-imaging research is consistent with the idea that men and women have relatively similar funny bones, says Eiman Azim, a graduate student who assisted with the experiment at Stanford.
There was no difference in the number of cartoons the 10 men and 10 women in the study found funny, how humorous they found them, or how long it took them to react with a laugh or a smile, says Mr. Azim, who is now studying at Harvard.
Both used the part of the brain responsible for processing language, when looking at cartoons, and the temporal lobe, which is involved in semantics and decoding.
But the women had more activity in their prefrontal cortex, which is involved in working memory, which allows someone to remember something for a short time, but not permanently. The limbic system, which processes emotion, was also more active, Mr. Azim says.
The study is published in today's Proceedings of the National Academy of Sciences journal in the United States.