NEW ORLEANS – Ladies, you may be able to fool your lover, but you cannot fool the machine.

A brain scanner can tell the difference between a fake orgasm and the real deal in women, neuroscientists have found. Different parts of the brain become activated depending on how authentic the thrill is. Aside from the giggle factor, the work could one day lead to new ways to treat sexual dysfunction in women, said neuroanatomist Gert Holstege, leader of the research team.

The findings, reported this month in New Orleans at a meeting of the Society for Neuroscience, topped a long list of new studies into how the brain behaves during sex and love.

A related study revealed that women suffering from spinal cord injury can still reach climax because a major nerve bypasses the spinal cord while conveying sensation from the genital area to the brain. In other work, scientists from Illinois reported that the brains of homosexual and heterosexual men become activated in similar areas when sexually aroused. And a third group of researchers announced that as the sex drive begins to shift toward permanent romantic attachment, other, unrelated parts of the brain light up under the scanner.

Research into sex and the brain may help the millions of people suffering from sexual problems, said Holstege, of the University of Groningen in the Netherlands.

“Now that we see how a big part of the brain is active,” he said, “we know where to look to try to work further with pharmaceuticals.”

His work on orgasm in women builds on earlier research on orgasm in men, using a brain scanning machine called positron emission tomography, or PET scans.

The studies in men revealed that a certain area of the brain, the amygdala, becomes less active just before ejaculation. The amygdala, which acts as a fear centre, may be shutting down so that men won’t be distracted on the way to orgasm, said Holstege.

At the same time, a region called the ventral tegmental area, or VTA, also becomes active. The VTA is a reward centre for the brain, releasing chemicals such as those that create the heroin rush in heroin addicts.

“It could be that we’re looking at the reward aspect of orgasm,” said Janniko Georgiadis, a graduate student on the team.

The VTA also lights up for women during orgasm. But unlike men’s brains, women’s brains also activate the periaqueductal grey matter, or PAG, an area that governs the fight-or-flight response. No one yet knows why the area becomes active in orgasm for women but not for men.

The experience of faking it was also unique to women. Big portions of the large structure called the cerebellum didn’t light up in fake orgasms as they did in true orgasms, said Georgiadis. Instead, the fake experiences activated brain regions that generally involve control of muscles.

The researchers had no trouble finding volunteers for the study. Eight heterosexual women came to the laboratory and lay with their heads in a scanning machine as their partners stimulated them clitorally.

The second orgasm study was a little more restrained. Neuroscientist Barry Komisaruk of the National Institutes of Health works with women with total spinal cord injuries.

“Many of the women we’ve studied have told us that their attending physicians told them that their sex life is over,” he said in a telephone interview. “Our emphasis is on the potential improvement of the quality of life.”

By comparing his results with the Dutch research, Komisaruk hopes to home in on the brain regions crucial for orgasm. Most of their results overlapped, but not entirely; that might be due in part to which parts of the body were stimulated. Everyone’s brain enjoys sex in the same way, as the study on homosexual and heterosexual men confirmed.

At the meeting, Michael Bailey of Northwestern University and colleagues reported on a study of 11 homosexual and 11 heterosexual men. All were asked to look at the same series of pictures, some erotic and some not. The subjects had to rate how much they found each picture arousing.

Apparently, it doesn’t matter whether a person is homosexual or heterosexual; the brain gets turned on the same way for both. In images from functional magnetic resonance imaging or fMRI scans, many of the same brain areas – those involved in emotional processing – show activity in both groups of men when shown an arousing picture.

“A few areas did come up a bit different,” said Bennett Barch, a student member of the research team. The brains of heterosexual men, for instance, showed greater rejection of erotic pictures of men than homosexual men did for erotic pictures of women.

Once sex becomes routine, people’s brains shift into a different pattern as they fall in love, according to a final study presented at the meeting.

“Romantic love engages a different brain system than the sex drive,” said Helen Fisher, an anthropologist at Rutgers University in New Jersey.

She and her co-workers took fMRI scans of seven young men and 10 young women who said they had been madly in love with someone for between one and 15 months. The researchers showed the subjects pictures of their beloved, interspersed with pictures of a familiar but neutral person (such as a family member) and distraction tasks (such as counting backward by 7’s from a very large number).

Just as during sex, the brains of people in love also became activated in the VTA, or reward system region. But other areas also lit up, Fisher said. Women showed more activity in areas associated with attention and memory recall, while men showed more activity in those associated with vision.

Love may have evolved as the last of three stages, Fisher speculates.

Sex would have arisen first as a method for seeking any possible mate. Attraction would have come next, helping to save time and energy by focusing on just one possible partner. And love would allow a pair to stay together long enough not only to have offspring, but also to raise them.