Your Brain on Sex

Posted by Catie Profaci on May 21, 2015 in Gender Month | 1 Comment

Men just want sex.  Women need intimacy.  Men just want sex.  Women crave commitment.  Men just want sex.  Women love flowers and date nights. Men just want sex. Women are all about that postcoital cuddling. Men just want sex.

NeuWriteSD’s gender month would not be complete without attempting to tackle the colossal gender stereotypes that arise when the conversation turns to sex.  It is socially acceptable–a status symbol even–for men to have many sexual partners, while promiscuous women are often debased as desperate and slutty, not only by men but also by fellow women.  A study suggesting that women are just as open to casual sex as men [1] garnered attention on social media lately, prompting heated discussion of sexual double standards.

The study involved two experiments; in the first, men and women were approached for a date or sex on campus or at a club.  In this case, men were more likely to accept offers than women.  In a second experiment, women and men were brought into the lab and shown pictures of members of the opposite sex, whom they were led to believe had already consented to a date or casual sex.  In this case, there was no significant difference between the percentages of men and women who consented to sex or a date, suggesting that social pressures strongly influence sexual behavior [1].

However, there is also plenty of evidence for bonafide gender differences in attitudes towards sex.  For example, another recent study showed that, after romantic priming and implicit testing (i.e., subjects were given a romantic context and then tested without their conscious realization), women wanted more sex.  Men, on the other hand, were less motivated to have sex in the romantic condition [2].

It could be argued that our social double standard with respect to sex takes root in evolutionary biology: it is reproductively advantageous for the male mammal, who makes more sperm than he knows what to do with, to inseminate as many females as possible in order to up his chances of passing on his genes.  And since the female mammal has to invest so much time and energy into carrying and raising a child, it is more advantageous for her to be picky–to find a male with rockin’ genes and make him stick around.

But then again, the evolutionary perspective is not so clear cut.  If natural selection has created a male race bent on sexual pleasure and a picky female contingent thirsting for commitment, how did the clitoris evolve to have two to three times more nerve endings than the penis?  The clitoris is, in fact, the only human organ solely devoted to pleasure and, yes, it belongs to the ladies. [For more fun clitoris facts, check out The Huffington Post’s report on the Cliteracy project–a recommended read for men and women alike! #getcliterate]

So what is neuroscience’s verdict? What happens in the brain during sex?  Are gender stereotypes a cultural construct? Or are men and women’s brains wired differently?  Are there true neurological differences in how men and women experience sex—desire, arousal, orgasm?

It can be argued that sex is one of the most primitive aspects of humanity—a behavior that we share with animals from ladybugs and leeches to llamas and lions.

From another perspective, however, human sex is an entirely different beast.  Not convinced?  Consider for a moment how often our uniquely human faculties (e.g. language, planning, high level thought processing, analysis of others’ behavior, empathy, etc.) are consumed by sex.  Quite often, for a behavior so primal.  I can promise you that male ladybugs do not spend days wondering if the hot ladybug across the leaf is DTF.

While scientists have been interested in the neural underpinnings of sex for as long as the concept of “neural underpinnings” has existed, due to technological limitations, early studies were either done in rodents or consisted of just psychological surveys.  The former, while helpful for uncovering some of the basic neural mechanisms of sex, could not paint a whole picture.  The latter, while getting at some of the human-specific components of our species’ relationship with sex, gave us no sense of the biology involved.

Technological advances have since changed how neuroscientists talk about sex.  Imaging techniques such as PET and fMRI have given scientists a window into brain activity during the different stages of a sexual encounter.  The results do suggest gender-related distinctions and, interestingly (but perhaps not surprisingly), there is far more segregation along gender lines during arousal than during orgasm.  While the findings themselves are along the lines of “this brain region was more activated in men than in women during genital stimulation”, it is fun to conjecture how these differences might manifest themselves in behavior.

While being manually stimulated by their partners, men had more brain activity than women in the ventral occipitotemporal cortex and claustrum [3].  The former is involved in processing visual imagery and the latter has been suggested as a site of multimodal integration (i.e., integrating a tactile sensation with an image).  So it sounds as if the guys were more likely to be relying on mental imagery.

Women, on the other hand, showed more activation in motor cortex than men did [3].  As implied by the name, motor cortex controls movement.  One researcher suggested that this might be due to increased female empathy skills—if females are better at taking on the perspective of others, they might show similar motor cortex activity patterns to their partner performing the stimulation [4].  My personal hypothesis is that the women were imagining what movements their partners could be making in order to be more successful in their endeavors.

Orgasm activity patterns were more similar across the board.  Both sexes showed activation in the cerebellar vermis and lots of deactivation in prefrontal cortex [3] (i.e., not so much thinking going on!).  A more recent study also showed pituitary activation during orgasm in women but not in men [5].  They suggested that this activation might be related to the pituitary releasing oxytocin—the “love drug”, which increases emotional attachment and also increases lubrication and orgasmic muscle contractions.

Besides differences in brain activation during sex, there is another interesting gender-related phenomenon worth contemplating.  A bunch of studies included measurements of the perception of arousal (essentially, “Are you turned on?”) and physical arousal (erection, lubrication, etc.).  Again and again men have shown higher concordance between the two measurements—they are better able to tell when they are physically aroused.  This effect seems to be driven by the fact that women display physical arousal to a wider range of visual stimuli even when they do not report feeling turned on.  For instance, when heterosexual men and women were shown video clips of female-female, male-male, and female-male sexual interactions as well as sex threat scenarios, men were physically aroused to male-female and female-female clips while women showed similar arousal across the board.  However, in their subjective reports of arousal, women reported being turned on by the male-female stimuli far more strongly than the other categories [6].

There are a few hypotheses as to why this might be the case [discussed in 4].  One possible reason is a previously shown gender difference in interoceptive awareness—it has been proposed that men rely more on bodily cues to define emotional state while external cues are more likely to shape a woman’s emotional state.  A second hypothesis is rooted in evolution: vaginal lubrication in response to unappealing sexual stimuli helped to protect women against pain/injury in unwanted sexual encounters (so remember, men: yes means yes; wet does not necessarily mean yes).

In summary, yes, men and women’s brains behave a bit differently during sex, and women seem able to automatically suppress perception of arousal in some cases, despite a physical response. But it’s not fair to say that men have a one-track mind while women are distracted by romantic rigmarole.  When it comes to orgasm, the playing field levels.  Breathing and heart rate increase.  Higher thinking ceases. And suddenly we don’t seem so different from the leeches or the lions.

References

1. Baranowski, A. & Hecht, H. Gender Differences and Similarities in Receptivity to Sexual Invitations: Effects of Location and Risk Perception. Arch Sex Behav (2015). doi:10.1007/s10508-015-0520-6
2. Dewitte, M. Gender Differences in Liking and Wanting Sex: Examining the Role of Motivational Context and Implicit Versus Explicit Processing. Arch Sex Behav (2014). doi:10.1007/s10508-014-0419-7
3. Georgiadis, J., Reinders, A. A. T., Paans, A., Renken, R. & Kortekaas, R. Men versus women on sexual brain function: Prominent differences during tactile genital stimulation, but not during orgasm. Human Brain Mapping 30, 3089–3101 (2009).
4. Chivers, M. L., Seto, M. C., Lalumière, M. L., Laan, E. & Grimbos, T. Agreement of self-reported and genital measures of sexual arousal in men and women: a meta-analysis. Arch Sex Behav 39, 5–56 (2010)
5. Huynh, H., Willemsen, A., Lovick, T. & Holstege, G. Pontine control of ejaculation and female orgasm. The journal of sexual medicine 10, 3038–48 (2013).
6. Suschinsky, K., Lalumière, M. & Chivers, M. Sex Differences in Patterns of Genital Sexual Arousal: Measurement Artifacts or True Phenomena? Arch Sex Behav 38, 559–573 (2008).