July 20, 2021
Written by: Lindsay Ejoh
Why is sex so rewarding? How does the brain respond to sex, and can that explain why humans find it so pleasurable? Our genitals have a high concentration of specialized nerve endings that, when properly stimulated, send signals to the spinal cord and regions of the brain that process touch and pleasure and activate our “fight or flight” sympathetic response1. At the height of an orgasm, brain activity peaks in regions like the posterior hypothalamus which causes increased breathing rate and blood pressure, and regions like the ventral tegmental area, substantia nigra, and nucleus accumbens, which are involved in reward, motivation, and addiction. Additionally, sex increases activity of the mesolimbic dopamine pathway, a neural circuit that is active during feeding, pain relief, and drug addiction2. Though having sex is not a basic necessity like eating, drinking, or avoiding pain, it is still highly rewarding and acts upon very similar brain pathways. Reproduction is essential for the survival of a species. Thus, it is advantageous for sex to act on similar motivational/rewarding brain networks as food.
In order to get a more detailed understanding of the biological basis of sexual reward, scientists use animal models such as rodents. One useful test is the conditioned place preference test. In this test, animals are placed in a box with two chambers: one associated with a sexual stimulus- a member of the opposite sex- and one without. After learning to associate one chamber with sex, the animal is placed alone in the two-chamber arena, and the amount of time spent in each chamber is recorded. If the rodent spends more time in the sex-paired chamber, this is evidence that it has developed a preference for that chamber, and that sexual stimulus may be rewarding for them.
Male and female rodents exhibit conditioned place preference for sex-paired chambers, but preference arises in females only when the female is in charge. In a 1997 study3, the conditioned place preference test was set up like previously described, except the doorway of entry between chambers was only accessible by the female, allowing her to move freely between chambers while the male stayed in one chamber. In this case, females developed a preference for the sex-paired chamber only when they were able to set the timing and pace of sexual intercourse. This indicates there may be differences between males and females in the rewarding aspect of sexual intercourse, with female rodents feeling more pleasure when having more control.
We constantly have competing motivational drives, and sex is only pleasurable in the right context. For example, hunger, poor sleep, and psychological stress can decrease sex drive4. Pain can lower sex drive as well, but sometimes pain during sex can be pleasurable, and facilitate orgasm rather than blunt it5. Studies in rodents and humans have also shown that sexual intercourse can increase one’s pain tolerance. Mice exhibit decreased pain responses to an electric shock when the shock is delivered during sexual intercourse. Additionally, human studies have shown that vaginal self-stimulation leads to increased pain tolerance6, and that orgasms lead to increased activity in brainstem areas known to release natural opioid molecules that mediate pain relief7. Rewarding stimuli are processed in the brain as pleasurable and motivate us to seek out more. It is evolutionarily beneficial this way- as having strong motivations to eat, drink, sleep, have sex, etc allow us to keep satiated, stay energized, and reproduce. Therefore, if you are having sex, enjoy it- your brain is wired to!
- Goldstein, I. (2000). Male Sexual Circuitry. Scientific American, 283(2), 70-75. Retrieved July 12, 2021, from http://www.jstor.org/stable/26058829
- Lenschow, C., & Lima, S. Q. (2020). In the mood for sex: Neural circuits for reproduction. Current Opinion in Neurobiology, 60, 155–168. https://doi.org/10.1016/j.conb.2019.12.001
- Paredes, R. G., & Alonso, A. (1997). Sexual behavior regulated (paced) by the female induces conditioned place preference. Behavioral neuroscience, 111(1), 123–128. https://doi.org/10.1037//0735-7044.111.1.123
- Burnett, C. J., Funderburk, S. C., Navarrete, J., Sabol, A., Liang-Guallpa, J., Desrochers, T. M., & Krashes, M. J. (2019). Need-based prioritization of behavior. eLife, 8, e44527. https://doi.org/10.7554/eLife.44527
- Dunkley, C. R., Henshaw, C. D., Henshaw, S. K., & Brotto, L. A. (2020). Physical Pain as Pleasure: A Theoretical Perspective. Journal of sex research, 57(4), 421–437. https://doi.org/10.1080/00224499.2019.1605328
- Paredes, R. G. (2014). Opioids and sexual reward. Pharmacology, Biochemistry and Behavior, 121, 124–131. https://doi.org/10.1016/j.pbb.2013.11.004
- Whipple, B., & Komisaruk, B. R. (1985). Elevation of pain threshold by vaginal stimulation in women. Pain, 21(4), 357–367. https://doi.org/10.1016/0304-3959(85)90164-2