For as long as bisexuality has been a recognized concept, it’s had its doubters — people skeptical that bisexuality is a real orientation. This denialism was easier in the past, when the culture was far less accepting and bi people were far less out and visible, but it still happens even today. Of course, this flies in the face of the evidence. Nearly 60% of the LGBTQ community is bi, and the percentage of people who are openly bi has increased steadily over time, outpacing every other LGBTQ subgroup. Researchers have even hooked bi men’s genitals up to sensors in controlled laboratory conditions and measurably demonstrated their physical arousal to both sexes. One of the most fascinating lines of evidence is brain scan studies, not just because of what they tell us about bi people, but also because of what they tell us about “straight” people too.
In a pair of studies published in the journal Scientific Reports between 2017 and 2018, a team of sex researchers scanned the brains of men and women with fMRIs while showing them erotic images and videos to see which regions activated. The first of the two studies, “Neural Correlates of Sexual Orientation in Heterosexual, Bisexual, and Homosexual Men”, focused on men, recruiting roughly equal shares of straight, gay, and bi men aged 25 to 50. To get the clearest possible results, the team set an unusually high bar for their bi participants, “requiring bisexual participants to have had at least two sexual partners and one romantic partner (of three months or greater duration) of each sex.”
The researchers found more or less exactly what one would expect to find: the reward-related regions of the brain, specifically the ventral striatum, showed greater activation for the preferred sex among both straight and gay men, whereas bi men “tended to show less differentiation between male and female stimuli.” In plain language, bi men’s brains lit up in just the way you would expect if they were, in fact, bisexual.
The second neuroimaging study, “Neural Correlates of Sexual Orientation in Heterosexual, Bisexual, and Homosexual Women”, focused on women, and here the results get more interesting. The same team recruited a pool of female participants comparable to the male study, with the same criteria for bisexuality. What they found was that lesbian women’s brains activated more for female stimuli, but bi women as well as straight women showed “more mixed patterns, with activations more responsive to female stimuli in sensory processing areas, and activations more responsive to male stimuli in areas associated with social cognition.” In other words, the brains of the lesbian and bi women showed the expected activity, but the straight women’s brains lit up in ways much closer to bi women.
This finding is not as surprising as it might seem at first. After all, polling shows that bi women significantly outnumber their male counterparts: the latest Gallup poll from 2026, for example, shows that 7.2% of American women are bi, compared to 2.5% of men. This could indicate that women are more likely than men to be bi, a prospect some people use to cast aspersions on whether male bisexuality is even real (again, see the above studies). But this gender gap could also indicate that women are more likely to come out as bi. As other surveys have shown, significant percentages of people who identify as straight — men as well as women — reveal bisexual attractions or behavior when asked probing survey questions that go beyond self-identification.
Far from a mirage, a phase, or some kind of social bandwagon effect, the research landscape as a whole has been very clear. It shows not only that growing numbers of people keep coming out as bi, and that bi people’s arousal and brain patterns behave in just the ways we’d expect, but also that a large number of people who may not think of themselves as bi probably are — they just don’t fully realize it yet.