WASHINGTON - THE brains of homosexual men resemble those of heterosexual women, while lesbians' brains show similarities with those of straight men, a study published on Monday showed.

Researchers at the Stockholm Brain Institute in Sweden investigated 'two separate parameters, both unlikely to be directly affected by learned patterns and behavior' in 90 men and women - 50 heterosexual and 40 homosexual - using magnetic resonance imagery (MRI).

Fifty people who took part in the study were also given positron emission tomography (PET) scans to study the amygdalae, masses of nuclei located deep within the temporal lobes which control arousal, fear and emotional responses, and hormonal secretions.

The results showed that the right-hand brain hemisphere was larger in heterosexual men and homosexual women, while homosexual men's and heterosexual women's brain hemispheres were symmetrical.

Homosexual men showed another brain similarity with heterosexual women in their amygdala connections, which process certain emotions, as did homosexual women and straight men.

'The amygdala has a key role in emotional reactions to external stimuli, including stress,' the authors of the study said, hypothesising that the amygdala of straight men and gay women could be 'wired for a greater fight-or-flight response,' reportedly more common in men.

The results of the study were published in the Proceedings of the US National Academy of Sciences. -- AFP