According to the researchers women are more likely than men to enjoy a good joke because they are expecting less from the punch-line.

In this novel imaging study, Professor Allan Reiss and colleagues, scanned the brains of 10 men and 10 women as they watched cartoons.

The imaging showed that women activate the parts of the brain involved in language processing and working memory more than men when watching funny cartoons, and were far more likely to activate with greater intensity the part of the brain that generates rewarding feelings in response to new experiences.

They found that while both groups on the whole found the same cartoons to be funny and displayed similar neurological responses, the women in the group used the part of the brain that processes rewards more than the men did.

While previous studies have shown gender differences in the use and appreciation of humour and the meaning and function of laughter, no previous research has examined sex-specific differences in the brain's response to humour.

Reiss says it appeared that the women had less of an expectation of a reward, which in this case was the punch-line of the cartoon, so when they did get to the joke's punch-line, they were more pleased about it.

Allan Reiss, MD, is the Howard C. Robbins Professor of Psychiatry and Behavioral Sciences and director of the Center for Interdisciplinary Brain Sciences Research, he says the results help explain previous findings suggesting women and men differ in how humour is used and appreciated, could lead to a better understanding of medical conditions such as depression and cataplexy, in which a sudden loss of motor control is precipitated by strong emotions, most notably humor.

Researchers know that a number of brain structures involved in language processing and memory, are involved in humour appreciation and in an earlier study Reiss and colleagues showed that the brain's reward center, which is responsible for the rewarding feelings that follow such events as monetary gain or cocaine use, is also activated by humour.

The researchers also found that the funnier the cartoon, the more the reward center was activated in women.

That was not the case in men who seemed to "expect" the cartoons to be funny from the start.

If subsequent studies show that women's reward center and other regions of the brain are more sensitive to emotional stimuli, including negative stimuli, that could help explain why depression strikes twice as many women as men, potentially leading to new therapies, says Reiss.

In a related study Reiss and his colleagues, including Dean Mobbs, now a Ph.D. student at University College London, found that personality traits, such as extroversion and introversion, affect how humor is processed.

Professor Reiss says that the combined results of the two studies suggest that humour taps into several neural systems associated with gender or personality and helps to explain individual differences in humor appreciation.

The studies are published in the current edition of the Proceedings of the National Academy of Sciences.