Using brain-scanning equipment, researchers said they discovered similarities in the brain circuits that deal with language, perhaps explaining why homosexual men tend to outperform straight men on verbal skills tests - as do heterosexual women.

The area of the brain that processes emotions also looked much the same in gay men and straight women - and both groups have higher rates of depressive disorders than heterosexual men, researchers said.

The study in Proceedings of the National Academy of Sciences, however, found that the brain similarities were not as close in the case of gay women and straight men.

Previous studies have found evidence that sexual orientation is influenced by biological factors.

More than a decade ago, neurobiologist Simon LeVay reported that a key area of the hypothalamus, a brain structure linked to sexual behaviour, was smaller in homosexual men than in heterosexual men.

The latest study, led by Dr Ivanka Savic of the Karolinska Institute in Stockholm, was significant in that it looked at areas of the brain that have nothing to do with sexual behaviour, suggesting that there was a basic biological link between sexual orientation and a range of brain functions.

Dr Savic and her colleagues used magnetic resonance imaging to measure brain volumes of two groups, each divided evenly between men and women: 50 heterosexuals and 40 homosexuals.

Brain scans showed that the brains of heterosexual men and homosexual women were slightly asymmetric with the right hemisphere slightly larger than the left, she wrote. The brains of gay men and heterosexual women were not.

Then they measured blood flow to the amygdala - masses of nuclei located deep within the temporal lobes which control arousal, fear and emotional responses, and hormonal secretions.

And they found it was wired in a similar fashion in gay men and heterosexual women as well as lesbians and heterosexual men.

LOS ANGELES TIMES, REUTERS, AGENCE FRANCE-PRESSE