THE saying goes that men are from Mars and women are from Venus, but scientists believe the real explanation for differences between the sexes lies in the structure of their brains.
For a long time it was thought that the basic architecture of the brain was the same in both sexes, with behavioural differences between men and women put down to hormones and social pressures.
But now an increasing amount of evidence is suggesting that male and female brains are built from significantly different genetic blueprints.
According to latest research, there are also differences in the circuitry that wires them up and the chemicals that transmit messages in the brain.
Scientists now believe there is good evidence that there is not just one kind of human brain, but two – each designed for equally intelligent behaviour.
Such findings could help develop more gender-directed treatments for dementia and other brain-related disorders.
Dr Jill Goldstein and colleagues from Harvard Medical School measured and compared 45 brain regions in healthy men and women.
They found that parts of the frontal lobe, which houses decision-making and problem-solving functions, were proportionally larger in women, as was the area which regulates emotions.
Meanwhile, other studies have found that the hippocampus, which is involved in short-term memory and spatial navigation, is proportionally larger in women than in men, which may come as a surprise given women's reputation as poor map-readers.
In comparison, in the men the proportionately larger areas included the parietal cortex, which processes signals from the sensory organs and is involved in space perception.
The amygdala region – which controls emotions and social and sexual behaviour – was also larger in men.
Dr Larry Cahill, a neurobiologist from the University of California, Irvine, said: "The mere fact that a structure is different in size suggests a difference in functional organisation." His team carried out brain imaging experiments on men and women, finding that sex influences how some regions of the brain are used.
When shown emotional images, men used a different side of their brain compared with women.
And while men were able to recall a general gist of the image, women were able to concentrate on the details.
Dr Cahill said this suggested men and women processed information from emotional events in very different ways.
Research also suggests that differences in the brain may explain why men and women have different reactions to pain.
Women are more likely to seek help for chronic pain than men, and certain painkillers work better in men than in women, other studies have found.
The research, published in New Scientist magazine, also points out that women are diagnosed with depression twice as often as men and their brains typically produce about half as much serotonin – a neurotransmitter linked to depression.
In comparison, men are more likely to be diagnosed with autism, Tourette's syndrome, dyslexia, stuttering, attention-deficit disorder and early-onset schizophrenia.
But much research has so far failed to take into account the differences between male and female brains, researchers said.
Most studies have been carried out on the brains of male animals or human male volunteers.
Dr Jeff Mogil, from McGill University in Montreal, Canada, criticised researchers for not looking at female brains, which could help lead to more targeted treatments for many illnesses. "It's scandalous," he said. "Women are the most common pain sufferers, and yet our model for basic pain research is the male rat."