Ask a Neuroscientist: Pain Physiology, Explained to a Bottom

by Hermes Solenzol

Imagine that you are being spanked…

Stop getting so excited! This is supposed to be a scientific explanation!

As I was saying, imagine that you are being spanked, and you are feeling that familiar stinging, warm pain in your behind. In reality, you don’t feel the pain in your bottom. You feel it in your brain. Your brain is what perceives everything, because that’s where consciousness takes place. Pain is not being hurt. Pain is not even your nerves responding to being hurt. Pain only happens when you become aware of the hurt. If you are anesthetized, there is no pain. The point is that for you to feel pain, a signal has to travel all the way from your buns to your brain. Many things can happen along the way that can make the pain signal become stronger or weaker. It helps to know what they are.


First, the pain signal travels from your bottom to your spinal cord. This is done by nerve fibers that have terminals embedded in your skin and, at the other end, in your spinal cord and your brain. There are two types of nerve fibers: A-fibers and C-fibers. The A-fibers do not generally transmit pain, only touch. They are thick and covered by a fatty envelope called myelin. These two things help them transmit signals very fast. On the other hand, C-fibers are thin and don’t have myelin. Because of that, they transmit signals slowly, at a speed of about one meter (three feet) per second. So it takes a substantial part of a second for the pain signal to reach your spinal cord. That’s why the first thing that you notice is that your master’s hand has landed on you bottom. The stingy, burning sensation builds up afterwards.

Are you still paying attention?

Nerve fibers are a special type of cells called neurons. Neurons are the main cells that process information in the nervous system. Unlike other neurons in the nervous system, however, sensory fibers are big and round, lacking their characteristic branch-like dendrites. Instead, they put out a very long fiber called the axon – nerves are just bundles of axons. The bodies of these neurons are all bundled together in the dorsal root ganglions, which are nested between the vertebras, one on each side. The axons forms a “T” just outside the ganglion: one end goes into the spinal cord, the other to your buns (or other parts of the body).

C-fibers make connections with other neurons in the part of your spinal cord closer to your back, called the dorsal horn. The dorsal horn is very important because this is where the pain signal can be increased or decreased. There are some neurons in back of your brain, a region called the brainstem, that send axons down the spinal cord. These axons meet the sensory axons in the dorsal horn and are able to turn up or down the incoming pain signals depending of what goes on in the brain. If the brain is in a state of fright, or simply unfocused, the pain gets increased. On the other hand, if the brain is focused, engaged in activity or sexually excited, the pain gets decreased. This effect is so powerful that people have suffered great injuries (for example, soldiers in battle) without feeling any pain at all. Some of these neurons from the brain stem release peptides into the dorsal horn (called opioid peptides, similar to endorphins) that are more powerful than morphine to eliminate pain. This is why when you get turned on during a spanking, you become a pain slut, and can’t get enough of it!

The journey of pain doesn’t end in the dorsal horn, however. Some neurons in the dorsal horn are in charge of sending the pain signal to the brain. There, there is a fork in the road, and pain goes two ways. One way, the pain signal reaches an area of the brain called the somatosensory cortex, which is in charge of keeping track of where pain in happening: in your bottom, not in your arm. The other way, the pain signal goes to two other parts of the brain cortex called the insula and the anterior cingulated cortex. These parts of the brain are in charge of telling you that pain is bad, bad, bad, and you should make it stop right now! This is what is called the “emotional component” of pain. They are also responsible for another property of pain called “saliency”, which means that, hard as you try, you cannot stop paying attention to pain. This is kind of convenient, because if Master wants to get your undivided attention, he just needs to give you a little pain. That’s why you need to get spanked once in a while…

Back to your poor, spanked bottom… As it gets hit over and over, it becomes red and hot. This is a bodily response called inflammation. As it turns out, C-fibers can also send signals the other way: from the spinal cord to your bottom. There they release some neuropeptides, among them substance P and calcitonin gene-related peptide (CGRP for short). CGRP increases the size of the capillaries in the skin, so there is more blood in the skin, which causes the redness. Substance P makes water (plasma) come out of the capillaries, causing swelling. Cells in the skin increase their metabolism, which causes the heating, sort of a localized fever. Depending of the extent of the damage, inflammation can last for a while after the spanking is over. This produces the nice afterglow sensation when you get sent to the corner. Inflammation serves to heal all the damage done, so that your poor bottom gets back to its original condition… until your next spanking!

Any questions?

Photography by Vivian Fu


HermesSolenzolBased in Los Angeles, California, Hermes Solenzol is a neuroscientist, and has been doing research on pain for several decades. In particular, he has been investigating endorphin release in rats. He has been a sadist for as long as he can remember and active in the scene for several decades.

Much of his writing is published in Spanish at Sexo, ciencia y espíritu, but there’s a great collection of articles on his English site, Sex, science and spirit. Along with a lot of BDSM wisdom, you’ll find thoughts on polyamory, communication, psychology and love.

He’s currently translating his first erotic novel from Spanish to English.

2 Comments Add yours

  1. Natty says:

    Do I get spanked for getting excited by this post anyway? ;-P I mean, it doesn’t get any hotter than spanking AND science together in the same post. Except maybe if there was a test involved… 😉

    Seriously, though, as someone who suffers from a chronic illness that includes chronic pain (which, as you know better than I, works a bit differently than the sort of acute pain you’re describing here) but is also a hopelessly perverted spanko, this was helpful in understanding what, precisely, is happening to the body during a spanking. I also really appreciated your piece setting the record straight on endorphins and spanking, especially as I think it helps explain the long-running argument in the spanking community about “punishment” spankings vs. erotic or “fun-ishment” spankings. Many in the domestic discipline camp have long argued that punishment spankings don’t have the same “feel” to them that erotic ones do and therefore work as a means of behavior modification. That because one is distressed about having disappointed one’s partner or been “bad,” the whole situation makes the spanking itself much more painful and unpleasant even if may not be as physically severe as an erotic spanking. The science as you describe it, appears to confirm this. Whether this actually works long-term for behavior modification is a whole other matter!

    At any rate, thanks for this and all your posts here as well as your blog. I’ve appreciated them very much!

    1. MasterMarc says:

      Hi Natty

      Thanks for your kind comment 🙂
      Behaviour modification is such a tricky subject. You’re right… a whole other matter!

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