If you think men and women have fundamentally different responses to sexual imagery, you're not alone. The advertising industry, for example, spends billions assuming men are more turned on by near-nudity than women. Yet neuroscientists are less convinced, and reviews of imaging studies suggest they're right to have doubts.
Studies that assess responses to sexual imagery based on self-description of arousal or blood flow to the genitals have obvious problems. More recently the search for more objective tests has led to functional magnetic resonance imaging (fMRI) scans to compare how the brains of men and women respond to sexual and non-sexual images. However, fMRI is expensive, so most studies have used very small sample sizes.
Ekaterina Mitricheva of the Max Plank Institute for Biological Cybernetics has resolved that problem by combining results from 61 studies, collectively involving 1,850 individuals.
Although details of the individual studies varied, each involved showing people videos and pictures and observing differences in their brains' responses to erotic versus neutral stimuli. The studies consistently show many areas of the brain are literally more “turned on” by sexual pictures than other material.
When Mitricheva investigated differences in responses between individuals, she found the responses depended not only on whether the material was sexual or not, but the format in which it was presented. On the other hand, less than 1 percent of the differences between individual responses was based on the viewer's sex – less than age or even the power of the machine used to take images.
Sexuality did influence responses, but sexual orientation accounted for only 15 percent of the total variation. Although a few studies included bisexual or trans individuals the numbers of each group were too small for statistically significant findings.
Mitricheva reports her findings in the Proceedings of the National Academy of Sciences, where she backs them up with another one: contrary to what many pseudo-psychology books will tell you the relevant areas of the brain are no more developed in men than women. That is, using a sample of 3,723 people, the brain regions that respond to sexual arousal contain the same amount of gray matter, on average, irrespective of whether they belong to a man or a woman.
The studies might be criticized on the basis that the participants were not randomly selected. People who volunteer for a study examining their brain's responses to sexy images may not perfectly represent the community as a whole and 72 percent of overall participants were men. Two-thirds of the studies were performed exclusively on right-handers, while the rest didn't say, and we can only guess if this matters. However, the fact that so many studies were used, and the results stood up if any one was removed adds credibility to the picture.
