Brain scan study: Bisexual and heterosexual women similarly aroused by male and female erotica

A new study provides more evidence that heterosexual women are just as likely to be aroused by erotic stimuli featuring men as erotic stimuli featuring women. But that does not appear to be the case for homosexual women.

The new neuroimaging research, published recently in Scientific Reports, found that gay and straight women had different brain responses to sexually-arousing stimuli. But there was not a strong difference between the brain responses of straight and bisexual women.

“Our interest in this topic came from previous research looking at physiological measures of sexual arousal. Surprisingly, women have tended to show substantial arousal to both male and female sexual stimuli, regardless of which sex they prefer,” explained study author Adam Safron of Northwestern University.

“Also interestingly, homosexual women seemed to have somewhat more directed (female-favoring) arousal responses compared with heterosexual women. We wanted to know what this might mean, so we looked to brain activity as another line of evidence.”

“What brain systems activate when women look at different kinds of erotica?” Safron said. “Would the reward system reflect the patterns from the sexual psychophysiology literature? We also wanted to see how heterosexual and bisexual women might compare. Would heterosexual women show more male-favoring preferences compared with bisexual women?”

The researchers used fMRI scans to examine the brain activity of 26 heterosexual, 26 bisexual, and 24 homosexual women while they viewed erotic material. The material consisted of pictures of nude men, nude women, and lesbian or gay couples engaged in sexual contact. Twelve video clips of men and women masturbating were also used.

Safron and his colleagues were particularly interested in an area of the brain called the ventral striatum, a dopamine-sensitive region that regulates feelings of pleasure in response to rewards.

“Our results were largely consistent with the sexual psychophysiology literature,” the researcher told PsyPost. “That is, we found that bisexual and heterosexual women were similarly nonspecific in their responses, with neither group strongly differentiating between erotica featuring men and women.”

“We also found that homosexual women differ from the other groups, preferring female to male visual sexual stimuli. This consistency between reward system activity and the sexual psychophysiology literature supports previous studies of genital arousal, suggesting that they may have also been measuring at least some degree of positive emotional response.”

Safron and his colleagues conducted a nearly identical experiment on men and published their results in 2017. That study, however, found that men’s brain activity closely corresponded to their sexual orientations.

Heterosexual men responded more strongly to images of women and gay men responded more strongly to images of men. Bisexual men, on the other hand, did not show a much of a different response to images of men and women.

The new study, like all research, has some limitations.

“An important caveat is that we don’t know the extent to which either reward system activity nor genital arousal actually reflect sexual desire,” Safron explained. “None of these measures correlate with each other particularly strongly.”

“We also don’t know why homosexual women are more specific in their response patterns and don’t know what differentiates bisexual from heterosexual women, since they both show nonspecific patterns.”

“Finally, it remains extremely challenging to find stimuli where we can trust that we’re validly measuring women’s sexual preferences,” Safron told PsyPost. “On average, women tend to be more discriminating than men in their feelings about erotica, and this can be a challenge for designing experiments. Rather than using a standard set of stimuli, future studies may want to use custom stimuli picked by each participant. Erotic narratives might also be promising.”

“It is difficult to overstate the influence of sexuality on our lives,” he added. “It is central to some of our strongest emotions and deepest commitments. Its influence is so pervasive that many of our actions would be incomprehensible without taking it into account.”

“Yet the study of human sexuality remains somewhat taboo, even though it’s of such clear scientific and humanistic importance. We may think that we understand ourselves sexually, but we can’t really be sure until we look. I think many people would be surprised to learn that most women show nonspecific arousal patterns in the laboratory.”

“And that’s part of what makes this work worthwhile, because we actually have a chance of learning something new. We hope that our work will help to inspire further research into these fundamental and fascinating questions.”

The study, “Neural Correlates of Sexual Orientation in Heterosexual, Bisexual, and Homosexual Women“, was co-authored by Victoria Klimaj, David Sylva, A. M. Rosenthal, Meng Li, Martin Walter and J. Michael Bailey.