last revised April 9, 2017.
Happy as a Clam at High Tide
A clam that lives near the shore may be exposed to predators (such as gulls and humans) when the tide is low and may be safe from these predators when the tide comes in and covers it. Clams may have cycles of anxiety and happiness as the tide comes and goes. But whatever the truth about clams, it seems that pleasure requires the absence of displeasure in all of its forms: pain, discomfort, anxiety, doubt. Our pleasures may cycle like the clam’s, but our own tides are not so predictable. So to fully understand pleasure, we will need to understand pain, a topic of the next chapter.
In this chapter I focus on touch as a source of pleasure. Clams probably don’t enjoy being touched as much as your horse or you, but being bathed in water of the right salinity and temperature is likely pleasurable enough that they will move down the beach if the tide disappoints.
When we think of human pleasure, we think of words running the continuum of happiness, joy, ecstasy and euphoria. We feel good. Such words beg for more precision, or at least a foundation in biology.
The Joy of Being Touched
It seems as if touch doesn’t merely increase your good feelings, but it also decreases your bad feelings.
For many years, researchers believed that the nerves of our skin could recognize just four kinds of stimulation: touch, heat, pain and itch. But there is growing evidence that cutaneous senses include another one that conveys information not just about touch, but about the pleasant properties of touch.2
Animals that are social by nature, such as many birds and mammals, have areas that can’t be reached by their own design and must be addressed either by rubbing against objects or by grooming by others. These areas — largely the head and neck — appear to be endowed with extra nerves that feel good when stimulated.
When two birds groom each other, one grooms the areas presented, while the other presents the areas for which grooming is desired and voices approval (if it feels good) and disapproval (if the grooming hurts). A pet bird who asks to be groomed will often do so by approaching to a favorite position, such as the middle of your chest, and putting his head down. Sometimes he will cluck his happy sound in anticipation of the pleasure to come, a signal that you can begin. As you gently rub the part he exposes to your finger, he will turn his head to give you other surfaces to work on. Clucks of pleasure will continue when your work feels good, but he will yelp if you pull a feather or push against a shaft and in any way cause pain. My birds seem to most enjoy ear rubbing. Their preferred regions are any part of the head down the neck an inch to the part of the neck they can reach. They have no interest in my attentions to any other body part.
Scratch your horse just right, and you’ll get a groan, lowered head, half-closed eye, and drooping lower lip. How a horse signifies his pleasure is discussed in the chapter on “The Horse’s Language.” Head grooming in birds and mammals evolved long ago. Head lice, which also evolved long ago, are now programmed to stay on the head and not go far enough down from there to risk destruction by their host. For birds, head grooming is also critical during moulting, for feathers that emerge are trapped in a sheath that needs to be broken open to release the feather. Such feathers must itch like crazy. But the programming that a bird has that makes head and neck grooming so pleasurable doesn’t turn on and off with moults or plagues of lice. It is on 24×7, and rubbing a little bird’s head will always give it pleasure — providing he wants you to do this and you use his approved technique.
The Joy of Touching
The animal kingdom seems to be loaded with nerves that feel good when stimulated. Moray eels sometimes hunt with other fish, and so are somewhat social. Their mouths open and close not in menace, but because they have no gill covers, and must open and close to force water over their gills. Sy Montgomery reports on a moray at an aquarium that had learned to get divers to scratch the inside of his mouth by opening his jaws exceptionally wide.3 This should not be surprising — morays visit “cleaning stations” where they rest with their mouths wide open inviting specialist fish to swim inside and remove parasites.
In his famous study of love in infant monkeys, Harry Harlow4 separated baby macaques from their moms and provided them with a pair of artificial surrogate moms. One group was given a cloth surrogate mother without food, as well as a wire surrogate mother with food. The little monkeys preferred to go without food and hug the cloth surrogate.
Teddy bears probably have no feelings. But children who love them certainly do. A variety of studies confirm what we already know about our teddy bear:5
- Children who play with teddy bears usually form attachments to them.
- Young children like to play with their bears, while older children move on to cuddling and sleeping with their bears.
- Teddy bears calm the fears of sleeping alone. It’s a scary job, but someone has to do it.
Moray eels, cockatiels, and horses all seem to love to be touched. But our baby macaques and children with teddy bears prove that touching can be wonderful, too. Touching and being touched would seem to be the same thing. But they are slightly different. I expect you could enjoy touching your horse as much as a baby macaque loved his cloth mother or you once enjoyed touching your teddy bear. Perhaps your horse will love being touched. Perhaps the two of you can do some happy loops.
A horse has an area of extra pleasure sensors, just like octopus and morays and cockatiels. I learned about their location when I first met G, my horse. Standing alone in a pasture, he had not been physically loved since he arrived at the non-profit that had intercepted his trip from track to slaughterhouse. I walked up to him and scratched his chest. He stretched his neck forward, lowered his head, half-closed his eyes, trembled his chin and groaned loudly. This wasn’t a horse. He was a dog. No feedback from him could have been better at convincing me that I had made him happy. His feedback made me happy, and we were locked in a loop. I scratched and scratched, then moved on to the bottom of his neck. Again he signaled his delight, and again we were locked in a happy feedback loop. This was the horse for me, I decided.
I most enjoy being kind when I receive a thank you from the recipient. Gifts that are not acknowledged don’t get repeated. Dogs get my love, but cats that can’t show this appreciation have to scratch their own necks. So I adopted G, a hedonist. It turns out he is very expressive about his pleasures. He uses his groan of ecstasy when defecating, sometimes when urinating, and when rolling in a dust bath. He uses it with me when I do his chest and neck. Now that I have Bud, a young mule, I have two boys that love to be scratched and rubbed. Bud is less demonstrative than G, slower to express his pleasure in my efforts. But I’m patient, and he does signal when things feel good, even if his signals are more subtle and slower to come. If your horse is not as expressive as mine, you’ll need patience and a good eye to find his signals that your work feels good.
What’s Under the Hood?
With a head rub, birds and horses tell us they have something big in common. Head rubs clearly result in pleasure to both, if delivered from someone they love and if they are in the mood. Their eyes close. Their heads lower. They emit sound of ecstasy. Other animals, such as the octopus, respond in just the same way to head rubs. Clearly there is something going on under the hood that accounts for this.
Erogenous Zones. Sensing physical pleasure begins at the skin. An erogenous zone is simply an area of the body that is more sensitive to touch than other areas. Nonspecific erogenous zones are areas of heightened sensitivity which contain a higher density of mechanosensory nerves. When these zones are stimulated, they produce pleasurable feelings, though not the same heightened sexual arousal that is produced by specific zones. Nonspecific zones in humans include the sides and back of the neck, the inner arms, the armpits, the fingertips and the sides of the chest. It turns out that the tongue and lips are sensitive, too and would be stimulated when one horse groomed another. So we have a motivation for allogrooming (grooming another of your species), and it turns out to be the same as the motivation for autogrooming (grooming yourself): it feels good!
Some or all of our erogenous zones may be powered by special nerves. An afferent is a nerve fiber that carries the signal of a sensory nerve from skin to spinal cord. There is a special kind of afferent — the C tactile (or CT) afferent. These are “slowly conducting unmyelinated (C) low threshold mechanoreceptive afferents” that respond to innocuous touch, and contribute to its good feelings.6 CT afferents respond selectively to gentle, slow skin stroking or caresses;7 the more frequently they fire, the more pleasant the sensation of skin stroking.8 In humans, these CT nerves are found in hairy skin, and not found in areas that have never had hair, such as the palms of the hands or soles of the feet. It appears that CT afferents are different than those afferents that sensitively detect touch, do not perform well in locating the exact source of touch, and are slower to conduct. CT afferents are just beginning to be mapped in humans, and have not yet been mapped in horses, but I suspect that mapping can easily be done with your fingers: rub a human or horse gently when they are relaxed, and record where your rubbing feels particularly pleasant. For a review of discriminative and affective touch, see McGlone, Wessbert, and Olausson (2104)9
Neurotransmitters and Hormones. There are neurotransmitters and hormones that are likely involved in pleasure, including dopamine, endorphins, and oxytocin. All of these are likely triggered by loving touch. When triggered, pleasure happens.
Special Circuits. The brain of all animals has three major pathways that activate behavior:
- A reward circuit which consists of a sequence of desire, action, and satisfaction. This dopamine pathway is central to reward-motivated behavior. Approach, pleasure, and learning are all managed by this circuit. CT afferents likely connect to this circuitry.
- A punishment circuit which involves a sequence of detecting danger then fleeing — or if that is not possible — then fighting. Fight is triggered if flight is not possible. Both fight and flight may lead to satisfaction if they are successful.
- A behavioral inhibition circuit. Freezing is triggered if neither fight nor flight are possible. This is useful if you are a small mammal and a predator is close by: freeze and you might not be spotted. It may also be useful if you are a congressman, and fear predation by tweet. Activating the inhibition circuit has negative consequences, particularly if it is activated frequently. Frequent activation generates anxiety, ulcers, psychosomatic illnesses, hypertension, cancer…
Feelings of pleasure use the reward circuit. This circuit, like the other two, produces effects that are byproducts of a more mysterious internal chemical process in the horse. I quote McBride et al10 for the technical explanation: “Low-frequency stimulation at acupressure points causes the activation of small-diameter nerve fibers within peripheral nerves.11 These synapse within the dorsal horn of the spinal cord and subsequently activate the spinal cord itself, the brain stem (reticular formation and periaqueductal gray area [PAG]), and the hypothalamus. Much of this initial neural activation appears to be opioid-mediated, especially within the ventrolateral periaqueductal gray area (vlPAG), with subsequent activation of serotonergic neurons within the raphe nuclei section of the reticular formation.12 It is this opioid mechanism that is considered responsible for the analgesic affects of acupuncture13 and the pleasurable or “well-being” sensation of acupressure or massage.14 The caudal vlPAG also has efferent pathways to the rostral and caudal ventrolateral medulla, caudal midline medulla, and the nucleus ambiguous regions; these are primary depressor regions, stimulation of which can result in bradycardia.15” McBride and colleagues only cite papers published before the discovery of CT afferents; it is likely that they did not know about such things, and probable that their discussion of the reward circuit would have referred to the “small-diameter nerve fibers within peripheral nerves” as CT afferents.
In other words, when certain tiny nerves at acupressure points are stimulated, the brain produces opioids that make us feel good, and sends signals that lower the heart rate.
The brain of a horse or human contains an area sometimes collectively called the limbic system, which sits below the cerebrum. This collection of brain power handles motivation, emotion, learning, and memory. It likely dates back to the first mammals, which means that those early mammals and all of today’s mammals are likely wired in basically the same way. With similar wiring comes similar results: all mammals can experience pleasure and pain, for instance. But motivation, emotion, learning, and memory are handled by different structures in the brains of birds, reptiles, amphibians, fish, and invertebrates, and there is much evidence that they can experience pleasure and pain.
I have a sea urchin who has no brain at all, I am told, so I am amazed that he has figured out all the good hiding spots in a huge aquarium (learning and memory), goes to the top of the tank just before feeding time (motivation, learning and memory, and a biological clock), and rapidly waves his spines when he senses nearby food (emotion). I suspect that when he gets his dinner that he, too, is happy as a clam at high tide. Not having a brain doesn’t seem to be a problem for him.
Pleasuring Your Horse
Where exactly are the best spots on the horse which give pleasure in allogrooming? We can watch horses to learn this — see the photos in the chapter on allogrooming. We may assume that horses groom each other at nonspecific erogenous zones, and that these areas have a high density of innervation with mechanosensory nerves. But we’ll have to wait for science to catch up to us on this one.
Mother nature gets credit for the joy of grooming, and the joy of being groomed. You and your horse get credit for the effort involved. Mother nature chose the head, neck, lower chest as nonspecific erogenous zones for the allogroomers of the future, who would inadvertently help remove parasites from these hard-to-reach areas. And Mother nature chose to endow tongue and lips as erogenous zones, to motivate those allogroomers.
What sort of touch feels good? It turns out that it is either a gentle touch or a stroke. What we do with our combs and brushes to a horse may or may not feel good. But certainly a rub with a towel, in the direction that the hair falls, would qualify.
1 Image source: https://pixabay.com/en/horse-mare-foal-nature-1268801/
2 McGlone, Francis, and David Reilly. “The cutaneous sensory system.” Neuroscience & Biobehavioral Reviews 34, no. 2 (2010): 148-159.
3 Montgomery, Sy. The soul of an octopus: A surprising exploration into the wonder of consciousness. Simon and Schuster, 2015. Pp 142.
4 Harlow, H. F. (1958). The nature of love. American Psychologist, 13, 673-685.
5 See https://scholar.google.com/scholar?hl=en&q=teddy+bear+attachment+play+calm&btnG=&as_sdt=1%2C21&as_sdtp=
6 Olausson, H., Lamarre, Y., Backlund, H., Morin, C., Wallin, B.G., Starck, G., Ekholm, S., Strigo, I., Worsley, K., Vallbo, Å.B. and Bushnell, M.C., 2002. Unmyelinated tactile afferents signal touch and project to insular cortex. Nature neuroscience, 5(9), pp.900-904.
7 Olausson, Håkan, Johan Wessberg, Francis McGlone, and Åke Vallbo. “The neurophysiology of unmyelinated tactile afferents.” Neuroscience & Biobehavioral Reviews 34, no. 2 (2010): 185-191.
8 Löken, Line S., Johan Wessberg, Francis McGlone, and Håkan Olausson. “Coding of pleasant touch by unmyelinated afferents in humans.” Nature neuroscience 12, no. 5 (2009): 547-548.
9 McGlone, Francis, Johan Wessberg, and Håkan Olausson. “Discriminative and affective touch: sensing and feeling.” Neuron 82, no. 4 (2014): 737-755.
10 McBride, S. D., A. Hemmings, and K. Robinson. “A preliminary study on the effect of massage to reduce stress in the horse.” Journal of Equine Veterinary Science 24.2 (2004): 76-81.
11 Kendall DE. A scientific model for acupuncture. Part 1. Am J Acupuncture 1989;17:251-68.; Kendall DE. A scientific model for acupuncture. Part 2. Am J Acupuncture 1989;17:343-60.
12 Kendall DE. A scientific model for acupuncture. Part 2. Am J Acupuncture 1989;17:343-60.; Kendall DE. A scientific model for acupuncture. Part 1. Am J Acupuncture 1989;17:251-68.; Nolte J. Organization of the brainstem. In: The human brain: an introduction to its functional anatomy. St Louis (MO): Mosby; 2001. p. 254-82.
13 Schoen AM. Veterinary acupuncture. Ancient art to modern medicine. St Louis (MO): Mosby; 2001.
14 Lund I, Yu LC, Uvnas-Moberg K, Wang J, Yu C, Kurosawa M, et al. Repeated massage-like stimulation induces long-term effects on nociception: contribution of oxytocinergic mechanisms. Eur J Neurosci 2002;16:330-8.
15 Henderson LA, Keay KA, Bandler R. The ventrolateral periaqueductal gray projects to caudal brainstem depressor regions: a functional-anatomical and physiological study. Neuroscience 1998;82:201-21. 20.; Chen S, Aston-Jones G. Extensive projections from the midbrain periaqueductal gray to the caudal ventrolateral medulla: A retrograde and anterograde tracing study in the rat. Neuroscience 1996;71:443-59. 21.