Women feel pain more than men because their brains are not "wired" in the same way, scientists believe. New research suggests that the basic architecture of the brain, and the way it operates, is different in the two sexes.

Previously the different sensitivity to pain between the sexes had been explained by hormones and social pressures. However, a series of studies have suggested that there "is not just one kind of human brain, but two", a male version and a female version.

It is well known that women are more likely to seek help for chronic pain than men, and the differences in the brain could explain this.

Men have a pain-suppressing circuit which links their brain to their spinal cord. When the circuit is activated by pain, endorphins are released and help lessen the feeling.

However, new studies have shown that the circuit does not release the analgesic endorphins in women.

Dr Anne Murphy at the University of Georgia in Athens has been examining the anomaly. She said: "This circuit is the Mecca of pain modulation in humans and all vertebrates, yet no one has asked how it is organised in females.

"This pathway is obviously not being used for pain in females."

In one experiment, scientists chemically blocked the pain receptors found in the brain and spinal cord of a male and female mouse. While this helped control the feeling in the male mice, it had little effect on the females.

Dr Jeff Mogil, who led the research at McGill University in Montreal, Canada, said: "It suggests females have a separate pathway."

The discovery could have an impact for how pain and illnesses in women are treated. Most of what is currently known about the brain comes from studies of male animals and male human volunteers.

A report, published in the New Scientist today, said: "If even a small proportion of what has been inferred from these studies does not apply to females, it means a huge body of research has been built on shaky foundations.

"Working out exactly how women are different could explain some long-running mysteries, such as why men and women are prone to different mental health problems and why some drugs work well for one sex but have little effect on the other."

Recent research has suggested that male and female brains are built from markedly different genetic blueprints, which create numerous anatomical differences.

There are also differences in the circuitry that "wires them up" and the chemicals that transmit messages between brain cells, as well as a proportionate size difference in some areas of a male and female brain.

"The mere fact that a structure is different in size suggests a difference in functional organisation," said neurobiologist Dr Larry Cahill of California University.

Dr Cahill carried out a series of brain-imaging experiments, in which he asked groups of men and women to recall emotionally charged images they had been shown earlier.

He also found that the different sexes used their brains in different ways.

Both men and women consistently recruited the same bundle of neutrons for the task. However, the men enlisted the right side of it, whereas women used the left.

And males recalled the gist of the situation whereas females concentrated on the details.