Women 'share same emotional brain traits' as homosexual men

Their similarities lie in the part of the brain responsible for mood and emotion.

Scans found that both homosexual men and straight women have symmetrical brains, with the right and left hemispheres almost the same size.

Conversely, lesbians and heterosexual men were found to have similarly asymmetrical brains, with the right hemisphere significantly larger than the left.

A study has revealed gay men and straight women have similar brain traits which might explain why they get along so well, like the characters on Will & Grace

The findings, published in the Proceedings of the National Academy of Sciences, provide the strongest suggestion yet that sexual orientation is determined as the brain develops in the womb, rather than shaped by outside influences.

Researchers at the Stockholm Brain Institute examined the scans of 90 volunteers, and also looked at blood flow to the amygdala area of the brain which plays a key role in emotional responses.

In straight men and lesbians, they found increased blood flow and more activity in the amygdala which feeds signals into other parts of the brain that trigger the 'fight or flight' response.

The right-hand side of the brain in heterosexual men and lesbians was typically 2 per cent larger than the left, while for gay men and straight women, the right side was on average 1 per cent smaller.

The study supports previous studies showing women and gay men may share language skills - and the ability to multi-task - but lack the spatial awareness for more practical skills, such as map reading.

A study from the University of London earlier this year revealed gay men and straight women shared a poor sense of direction and were more likely to navigate by looking at landmarks.

Neurobiologist Ivanka Savic, who led the Swedish study, said more research would be needed on the brain symmetry of newborn babies to determine whether homosexuality can be determined at birth.

She said: 'These differences might be laid down during brain development in the womb, or they could happen after birth, though it could very likely be a combination of the two.

'The observations cannot be easily attributed to perception or behaviour. Whether they relate to processes laid down during the foetal or postnatal development is an open question.'

The research is part of a larger effort to identify differences between the male and female brain, in the hope they will shed light on why some mental disorders affect men and women differently.

For example, major depressive disorders are far more common and persistent in women, while autism is around four times more common in boys than girls.