But what the male brain may lack in conversation and emotion, they more than make up with in their ability to think about sex....  

Dr Brizendine says the brain's "sex processor" - the areas responsible for sexual thoughts - is twice as big as in men than in women, perhaps explaining why men are stereotyped as having sex on the mind.

Or, to put it another way, men have an international airport for dealing with thoughts about sex, "where women have an airfield nearby that lands small and private planes".

Studies have shown that while a man will think about sex every 52 seconds, the subject tends to cross women's minds just once a day, the University of California psychiatrist says.

Dr Brizendine, whose book is based on her own clinical work and analyses of more than 1,000 scientific studies, added: "There is no unisex brain.

"Girls arrive already wired as girls, and boys arrive already wired as boys. Their brains are different by the time they're born, and their brains are what drive their impulses, values and their very reality.

"I know it is not politically correct to say this but I've been torn for years between my politics and what science is telling us.

"I believe women actually perceive the world differently from men.

"If women attend to those differences they can make better decisions about how to manage their lives."

Other scientists, however, are skeptical about the effects of testosterone on the brain and say many of the differences between the male and female personality can be explained by social conditioning, with a child's upbringing greatly influencing their character.

 *The Female Brain, by Dr Luan Brizendine