Women's brains are more tightly packed with cells in the area that controls mental processes such as judgement, personality, planning and working memory, researchers have discovered.

A team from McMaster University, Ontario, Canada, found that women have up to 15% more brain cell density in certain areas of the frontal lobe, which controls so-called higher mental processes.

The cells are found in areas that make connections with other parts of the brain, such as the limbic system which is thought to play a major role in the emotions.

However, as they get older, women appear to shed cells more rapidly from this area than men. By old age, the density is similar for both sexes.

Researcher Professor Sandra Witelson said it was not yet clear what impact, if any, the difference had on performance.

However, she suggested that the difference might account for the fact that women are ten times more likely to develop some psychiatric conditions such as panic attacks and anxiety disorders.

There is some evidence to suggest that hormone replacement therapy can reduce the loss of women's brain cells as they get older.

Risk of disease

Dr Tonmoy Sharma, a consultant psychiatrist at Stonehouse Hospital, Dartford, UK, said the greater density of cells did not mean that women could out-perform men.

He told BBC News Online: "Women have smaller brains, but there is no difference in the mental performance of men and women.

"The greater density of cells could be one way by which nature ensures that women can perform adequately despite the smaller size of their brain."

Dr Sharma said it was possible that the fact that women shedded cells at a greater rate put them at a higher risk of neurodegenerative diseases.

Alzheimer's disease, for one, is more common among women. But he said there were many factors which could come into play.

Dr Richard Harvey, research director for the UK's Alzheimer's Society, told BBC News Online the fact that women lived considerably longer than men was by far the most significant factor.

The findings were presented to the Society for Neuroscience meeting in San Diego, US.