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The Neuroscience of Spanking

What happens in the skin, the nerves and the brain during a spanking, and how it can help you improve your experience.

Does a spanking produce pain or just sensation?

Some people say that they are into spanking, but not into pain. Because, you know, if they were into pain that would mean that they are (gasp) masochists! So they say that they like gentle spankings that are just “sensation”, not pain.

What does neuroscience have to say about that?

Pain is not just a strong tactile sensation. Believe or not, this was strongly debated for some time among pain scientists. Nowadays, it is clear that pain and tactile sensations are carried by different neurons, from the body all the way into the brain.

The different types of fibers innervating the skin. Diagram courtesy of Dr. Stephen McMahon, King’s College of London, modified by the author.

There are three types of nerves that receive signals from the skin: C fibers, A-delta fibers and A-beta fibers. They differ on their diameter and whether they have myelin or not. Myelin is a coat of fatty tissue produced by glial cells which envelops the nerves, leaving gaps called nodes of Ranvier. Two types of nerves have myelin and are called A-beta and A-delta fibers, while the third type, called C-fibers, does not have myelin. C-fibers are also thinner.

Most C-fibers transmit pain, but some transmit heat, cold or itch. A-beta fibers transmit only tactile sensation. Some A-delta fibers transmit pain and others tact. Therefore, pain and tactile sensations are entirely different things.

Touching, caressing and rubbing stimulates A-beta fibers. The impact involved in a spanking stimulates C fibers and A-delta fibers. Of course, since impact involves touching, it also activates A-beta fibers. However, even the gentlest spanking activates pain fibers and, therefore, should be considered pain. What happens is that low intensity pain is not unpleasant and, in fact, can be quite pleasurable.

So, yes, spanking causes pain.

Stingy versus thuddy pain

I used to think that a spanking is pleasant because it produces stingy pain. By that I mean a pain that is felt in the skin and is sharp and sparkly. It also leaves an after-sensation of warmth. However, later I found spankees who prefer thuddy pain. By that I mean a dull, achy sensation that is felt deeper than the skin, in the muscle, and does not leave a warmth afterward.

Different types of C and A-delta fibers produce stingy and thuddy pain. Stingy pain is actually two sensations: an immediate, sharp one carried by A-delta fibers and a later one that is more dull and hot, which is carried by the C fibers. But both of them are located in the skin. Thuddy pain is carried by C fibers in the muscle.

A quick slap in the butt produces stingy pain. A punch or a kick in the butt produces thuddy pain. Stingy pain requires speed. Thuddy pain requires mass.

Spanking is really about stingy pain. People who prefer a thuddy sensation would do better being caned or paddled.

Click here to read Mark’s interview

To improve the quality of the sting, the spanker should:

  1. aim for the skin instead of sending the impact deep into the glutes;
  2. move the hand quickly and do not put a lot of weight into it;
  3. curve the hand to the shape of the buttock, so the entire palm contacts the skin at the same time;
  4. relax the wrist and the hand, so the hand goes rubbery instead of rigid like a paddle.

The later will also prevent the spanker from damaging his wrist and knuckles from the repetitive impact. This type of injury will not be felt until the next day because it involves deep-tissue inflammation. It does happen!

Why does a spanking feel hot?

Because many C fibers have a peculiar protein called TRPV1, which is a sensor for heat. TRPV1 was discovered as the receptor for capsaicin, the chemical found in spicy peppers that makes them hot. It sits on the membrane of neurons and forms a channel that when activated lets sodium and calcium ions into the cell. This triggers the firing of action potential in the C fibers, which send a pain signal to the spinal cord and from there to the brain.

TRPV1 channels are opened mainly by high temperatures. However, they are also activated by capsaicin and other chemicals, by acid (that’s why vinegar or lime juice make hot peppers spicier) and by chemicals released by skin cells when they are damaged. When you get spanked, the C fibers that express TRPV1 get activated. That feels hot because these fibers encode heat. Besides, cells in the skin of the butt release chemicals that directly activate TRPV1.

You can use hot peppers to increase the hot afterglow sensation produced by a spanking. I wrote this article explaining how to do that.

Why does the butt turns red?

A curious property of sensory nerve fibers is that they can transmit action potentials in both directions: from the body to the spinal cord, but also from the spinal cord to the body.

Cell bodies and axons of C fiber neurons in the dorsal root ganglion of a rat. Green label is the neuropeptide substance P; bright red label is the mu-opioid receptor. Confocal microscope image by the author.

Sensory nerves are neurons whose body is located in the dorsal root ganglia, which are nested between the vertebras of the spine, just outside the spinal cord. They do not have any dendrites, just an axon that can be up to several feet long. Inside the ganglia, these axons divide into two branches, one of which goes to the body and the other into the spinal cord. Action potentials travel both ways through these two branches.

When pain builds up in your butt during a spanking, the spinal cord neurons that receive those pain signals start talking back to the C fibers that carry them. The C fibers then send action potentials from the spinal cord to the skin of the buttocks. When these action potentials reach the skin, they make the C fibers release two neuropeptides: calcitonin receptor-related peptide (CGRP) and substance P. Together, these peptides make the capillaries of the skin expand. Capillaries are tiny arteries and veins that supply blood to the organs. Because there is more blood in the capillaries when they expand, the skin looks red.

CGRP and substance P also make the capillaries in the skin leak plasma from the blood, causing the skin to swell. Heat, redness and swelling are the hallmark of inflammation. Hence, a spanking causes inflammation of the skin. I know, I know! Inflammation has a nasty reputation these days. But it is not always bad. In fact, the increased blood flow in the skin nurtures it and makes it stronger. That’s why people who get spanked regularly get a thick skin in their bottoms that makes them able to withstand harsher spankings. In the BDSM community, they are known as iron butts.

Are bruises bad?

Bruises develop because sometimes capillaries leak not just plasma, but also red blood cells. These cells get trapped in the skin and die, releasing their hemoglobin, the red protein that they use to carry oxygen. Hemoglobin is initially red, but as it degrades it produces chemicals of different colors — yellow, green and blue — that give bruises their distinctive look. The skin is an organ that is well equipped to deal with this, so bruises in the skin are not something to be worried about. However, bruises in the muscle do not heal that easily and should be avoided.

Click here to read Sank’s article

People differ vastly on how their skin responds to a spanking. I know a woman who is quite masochistic and gets frustrated because her bottom would not turn red even with the strongest spanking. In contrast, one of my past lovers would get bruises in his bottom that would last days, with just a mild spanking. As I said above, with regular spankings the skin will grow thicker and will bruise less. Get to know your body, know what you want, and play accordingly.

But why do I like to get spanked?

The attractive of spanking involves many physical and psychological aspects, so this question does not have a simple answer. Besides, different people may enjoy spanking for different reasons.

Staying within the physical realm without getting into the psychological stuff, many people clearly enjoy the pain produced by a spanking. And they don’t just like it a little, I have seen many guys orgasm during a spanking with no other physical stimulation. How can that happen? Does the butt have connections to the pleasure centers of the brain?

The neuroscience of pain gets quite complicated once we move from the sensory nerves into the spinal cord and the brain.

In the spinal cord, C fibers make synapses with neurons that have the receptor for substance P, the neurokinin 1 receptor. These neurons send axons up the spinal cord to two areas of the brain, the parabrachial nucleus and the thalamus.

The parabrachial nucleus is connected to the amygdala, the part of the brain that produces fear, stress and excitement. In turn, the amygdala connects to the paraventricular gray, which is the origin of neuronal pathways that release endorphins. It also connects to the locus coeruleus, the origin of noradrenergic pathways. So, in an environment in which we feel safe and fear is kept in check, this parabrachial — amygdala pathway could lead to the endorphin and noradrenaline highs.

At the thalamus, the pain pathway branches to three sites in the cortex. The first is the somatosensory cortex, which tells us in what part of the body pain is happening (in the butt, you dummy!). The second is the insula, which is an area in which pain and pleasure meet each other. It is involved in orgasms, which could explain why spanking can produce them. But it also has a role in many other emotions. The third area is the cingulate cortex, an area that has an important role in motivation.

Click here to read Boy Kevin’s interview

Too much? Well, who said that neuroscience was easy?

Here are a few take-home messages…

  1. Spanking may take some getting used to. Start gently and do it regularly to build skin resistance and carve the neuronal pathways that will lead to increasing pleasure.
  2. Spanking is an art that needs to be learned. Hitting the butt willy-nilly will not do it. Both the spanker and the spankee need to work at it.
  3. It isn’t weird that spanking is pleasurable. The machinery to make it happens is all there, in the brain.
  4. For a spanking to be enjoyable, we need an environment that makes us feel safe. It is important to have a good emotional connection with the spanker, a clear understanding about what is going to happen, and a safeword to stop the spanking if things go wrong.
  5. There are many positions in which to be spanked, which can affect its physical and psychological effects.
  6. Orgasming from spanking may happen, but don’t seek it out. Spanking is excellent foreplay or just an erotic activity to insert into your love life.

Header-pic: Boynapped with Sebastian Kane as spanker. Click here to read his spanking interview.

Hermes Solenzol
Hermes Solenzol
University professor. Neuroscientist doing research on pain. Writes about science, philosophy, politics and kinky sex.

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