STRONG evidence that sexual orientation is “hard-wired” in the brain has been found by British scientists.

A study of the startle response — the blinking reaction to sudden loud noises — has revealed significant differences between homosexuals and heterosexuals.

Qazi Rahman, of the University of East London, led the research. He said that it was the first to identify a neurological difference between homosexuals and heterosexuals that could not have been learnt.

“The startle response is pre-conscious and cannot be learnt,” he said. “It is mediated by an ancient region of the brain called the limbic system, which also controls sexual behaviour. This is very strong evidence that female sexual orientation at least may be ‘hardwired’ in this region.”

Scientists behind the study said that it was possible that exposure to differing levels of testosterone in the womb could affect brain development, fixing sexual orientation and the startle reflex for life.

The subjects were unexpectedly startled with a loud noise and the speed and strength of their response measured.

Heterosexual men had an average score of 40 per cent, compared with 32 per cent for gay men. Among women, lesbians scored an average of 33 per cent, compared with 13 per cent for other women. The findings are published in the journal Behavioural Neuroscience.

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