Many studies have shown that during intercourse, pain sensations are reduced or may even be perceived as pleasurable. Why is this advantageous? How does it happen? We’ll look into more of that here!
What’s the role of evolution?:
Throughout time, species evolve. The basic idea of evolution is that over time, an organism develops certain characteristics that give it an advantage over other members of its species. These advantages make it more likely that the organism will pass on its genes.
So if species have evolved in ways to make them more likely to pass on their genes, then the act of copulation must have evolved in ways to encourage the behavior. This is why orgasms are such a pleasurable experience. The immense physical pleasure that happens with an orgasm encourages the organism to try to have intercourse again, and the more times the organism has intercourse, the more likely they are to pass on their genes.
What is analgesia?:
Analgesia is the reduction in the feeling of pain. You may have experience with this. Maybe at the dentist, you’ve been given medicine so you can’t feel them filling in your tooth. Maybe during a sporting event, you’ve had a minor injury, but there was so much adrenaline that you didn’t notice.
Why is it important during sex?:
If you are less likely to feel pain during sex, then you are more likely to engage in intercourse, and consequently pass on your genes. Without analgesia, sex could be a painful experience, which would discourage passing on genes.
How does pain reduction occur? The Autonomic Nervous System:
To understand how pain reduction plays a role in reproduction, we first need to have a brief discussion of the parasympathetic and sympathetic nervous system. The parasympathetic nervous system is involved in processes that save energy. The parasympathetic nervous system calms you down, and is involved in functions such as digestion and salvation. Your body is usually in parasympathetic tone, in order not to use up too much energy. It is necessary for you to be in a calmed, parasympathetic state in order to become aroused.
The sympathetic nervous system, on the other hand, is involved in energy expending processes. It is activated during stressful situations. It’s often associated with the “fight or flight” response. It causes adrenaline to be released, blood vessels to constrict, pupils to dilate, and increases heart rate. Sympathetic tone is what is necessary for your body to achieve orgasm.
Think about it. In order to become aroused, there needs to be a somewhat calm atmosphere that suggests sexual activity may occur. During this part, your body is under parasympathetic tone. Then, while having intercourse, your heart rate rises, and your sympathetic nervous system kicks in. Part of this activation is the decreased sensitivity to pain. As intercourse progresses, the body becomes less and less sensitive to pain so that the motions can continue until orgasm occurs.
Neural Mechanisms: What in the brain causes analgesia?:
Pain reduction in the body usually happens because of the endogenous opioid system. Opioids are neurotransmitters that help modulate circuits in the brain responsible for pain reduction. They are the body’s natural painkillers, and can produce feelings of euphoria. For example, when you exercise, endorphins are released, an endogenous opioid that makes you feel good after.
So how do opioids work in the context of reproduction? There is a ton of ongoing recent research in this area. One proposed mechanism states that endogenous opiods interact with excitatory amino acids and nitrous oxide in order to regulate the release of certain hormones involved in reproduction. So, it is proposed that opioids inhibit glutamate, a neurotransmitter that excites neurons, which activates GnRH neurons. GnRH neurons are responsible for releasing different sex hormones. In other words, endogenous opioids stop glutamate from interacting with different nerves that regulate certain sex hormones. (Broxmeyer and Tian, 1997)
How do we know analgesia happens during sex?:
Many experiments support the idea of analgesia during sex. Experiments show that when rats are administered an electric shock before and after intercourse, they show reduced sensitivity to the electric shock after intercourse. To show this is what is occurring, the researchers measure how long it takes the rat to respond to painful stimuli, the electric shock. After sex, when the process of analgesia has happened, the rats take longer to respond to the shock. We use this as a proxy to measure pain sensitivity. (Gomera, 1994)
This effect could be reversed by treating the rats with naloxone, a drug that blocks opioid receptors. If opioid receptors are blocked, that means they cannot do their job in the brain, and can not cause any analgesic effects. Therefore, under the treatment of naloxone, the rats respond the same to the electric shock before and after sex, which means no analgesia occurred. (Szechtman, 1981)