The Neurobiology of Sex

What goes on in a man’s head during sex? According to a new study from Japan, it all comes down to the precise timing of two brain chemicals: dopamine and acetylcholine. Their findings in male mice provide fresh insights into the neurobiology of sex and may perhaps inspire new approaches for treating erectile disorders.

The Brain During Sex

Sex activates multiple areas of the brain. These regions play a key role in regulating arousal and pleasure at different stages. The hypothalamus coordinates arousal, triggering the release of testosterone to get the body ready. The amygdala influences how we feel, whether it’s excitement or even a bit of nervousness. Inside the brain’s “reward center,” elevated dopamine generates pleasure, a crucial part of sex.

Until now, it has been a mystery how various brain regions and chemicals work together to guide sexual behavior. According to senior author Qinghua Liu of the National Institute of Biological Sciences in Beijing, “The study revealed the dynamics of how different chemicals work together in the brain to regulate the transitions through different stages of male sexual behavior.”

Brain Chemistry in Action

In this study, each mouse was placed in an enclosure with a female mouse. The courtship began as the male mouse approached and began to sniff out the female. Once both were ready, the male mouse went through cycles of mounting and mating before reaching ejaculation. All the while, the mice wore wires attached to their heads that recorded neural activity in the “reward center.” They specifically tracked changes in neurotransmitters, the brain’s chemical messengers.

From arousal to ejaculation, there was a steady increase of dopamine in two distinct areas of the “reward center.” However, in one of these regions, dopamine levels appeared to fluctuate during mating, seemingly synchronized with each thrust. It seems that the closer the animals were to ejaculation, the more dopamine was produced in this part of the brain’s “reward center.”

These dopamine spikes were coupled with another neurotransmitter called acetylcholine. Acetylcholine helps activate our muscles and coordinate movement, including those involved in sex. It seems that this brain chemical not only coordinates the physical aspects of sex but also influences different states of intimacy.

To determine how acetylcholine and dopamine work together, the team used red and green fluorescent markers to track their activity in the brain’s “reward center.” The recording showed that arousal first triggers the release of acetylcholine, followed by dopamine about six seconds later. Acetylcholine levels remained dominant as the male mouse mounted the female, suggesting that this chemical plays a greater role in the early stages of sexual behavior. However, by the time the animals began mating, the two were nearly synchronized with the mouse’s movements.

This continued until dopamine began to decrease, and then a sudden spike occurred. This sharp increase in dopamine marked the end of the mouse’s sexual encounter: ejaculation. If acetylcholine drives the early stages of sex, dopamine seems to steer the process to the end. When the team used optogenetics to enhance certain dopamine receptors that inhibit their effect, the mice stopped engaging in sexual behavior completely.

Conclusion

Although human sexual behavior is more complex, our brains are not that much different from mice. These findings could have big implications for understanding and treating issues like erectile dysfunction or premature ejaculation. It is a fascinating glimpse into what goes on in our brains during sex.