Touch: The Science of Hand, Heart, and Mind (David J. Linden)

Posted: January 1, 2018 in nonfiction
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When I was at university, my best friend liked to ask generic conversation-generators when the talking flagged. One of them was, “If you had to lose four of your five senses and could only retain one, which would you keep?” I thought about it for a minute. When I say a minute, I’m exaggerating. People sometimes miss the fact that I’m thinking through a question instead of responding instinctively because I do it quickly, but I did run through a few scenarios, of seeing without hearing or feeling, or hearing without tasting or seeing, and I answered, “Touch.” Even at that time of my life, as extra-virgin as your olive oil and seldom touched by anyone, I understood the emotional significance of physical contact, and I knew how lonely my life was without handshakes, hugs, or even more casual touch. The other things I would miss a lot but I can deal without, seeing sunsets and paintings, hearing music or voices, tasting my food or smelling flowers, but the tactile sense is the essential.

touch

Linden’s book is about this tactile sense, as is obvious from the title, but it’s not much about what I just mentioned. It’s about physiology, primarily about nerve endings and brains and skin. I’m not used to this type of discourse, so while I tried to read it all at a go during the vacation, I got through a couple of chapters and had to take a break. My mind got full. The next day I read the entire rest of the book, and it went quickly and easily because of the background I got in Chapter 2. This experience started me thinking about how I learn. I was never much for studying actively, never very good at reviewing my notes or preparing for examinations. I tried a few times, with friends who were Honors students, but they never invited me back to their sessions. My brain works like this: I read it once, and then I have to move along and do something else, like watching television or reading fiction. The processing goes on subconsciously while my attention is elsewhere. But when I go back to that knowledge, it’s there where I need it to be. It doesn’t disappear the way that it seems to do for other people. The repetition of building on previous knowledge helps, and the spider web metaphor for learning is true for me as well as it is for others, but the sort of rote repetition for the purpose of passing a test is unhelpful, unnecessary, and hard to focus on.

What’s that spider web thing, Occ Man? Spider webs gain their strength by intersecting and making connections. A single strand is easily avoided or broken, but a web of several concentric circles with numerous radial strands is effective at trapping all sorts of prey. Likewise, facts that are unconnected to previous knowledge or our own experience, what theorists call inert knowledge, are weak and easily forgotten. Teachings that connect to a student’s experience or to previously acquired information are stronger and easier to retain. The more connections a student makes, the more likely she is to remember. Which I suppose is why I couldn’t study with the Honors students – they were repeating the same information in the same way divorced from context, not making connections to anything. It worked in the short term and gave them the grades they needed for scholarships and awards and things, but it wasn’t the same as loving knowledge for its own sake or learning the material effectively. If they ever needed that information again, it wasn’t waiting for them.

As previously implied, Chapter 2 is about the basic mechanisms of tactile sensation, how we recognize items by touch and perceive motion. It gives the necessary information about the types of nerves we have in our skin, the types of skin we have on our bodies, and where in our brains we analyze and sort this information. Chapter 3 is about the different ways we perceive being touched by other people and the emotional content of physical interactions, which leads into Chapter 4, about sex. Chapter 5 is about our perceptions of temperature, Chapter 6 is about pain, and Chapter 7 is about itching. Add an introduction (about social touch) and a conclusion (about tactile illusions) and you’ve got two hundred pages of physiology. The notes are sort of interesting, a range from the overly technical:

For you hard-core anatomy mavens: Neurons that carry information from the mechanoreceptors have axons that ascend in the region of the spinal cord called lamina IV of the dorsal horn. Mechanoreceptor axons from the lower body, below the seventh thoracic vertebra, contact neurons in the gracile nucleus of the brain stem, while those of the upper body form synapses on neurons in the adjacent cuneate nucleus. The gracile and cuneate neurons send their axons to a particular subdivision of the thalamus called the ventroposterolateral region through a midline-crossing pathway called the medial lemniscus. These thalamic cells then project to the primary somatosensory cortex. In later chapters, we’ll discuss skin sensors for erotic touch, pain, itch, and temperature, which take a different path in both the spinal cord and the brain.

To the extremely casual:

And don’t imagine that it’s only gay or bisexual men who like stimulation of the anus, rectum, and prostate. My old pal C., who runs an Internet sex-toy shop, says, “You’ll never go broke selling devices for straight guys to put in their butts.”

Which makes me wonder if I ought to give up on education and devote my life to selling vibrators.

So. Things that were new and useful in conversation. Itching and pain are actually quite different, and this fact is actually relatively new knowledge. In 1999 I was told that itching is just a very mild pain, and that acetaminophen would help with mosquito bites, but we now know that the truth is different. Itching and pain are perceived by different cells and processed in the brain differently, and there are actually different types of itching. Histamine is an obvious culprit and there are numerous antihistamine creams, but it’s not the only cause. There are itches that antihistamines and acetaminophen don’t help with because they’re caused by other chemicals in the body. (Just to review, the British name for acetaminophen is paracetamol, because the generic name for the compound is para-acetylaminophenol and we shortened it differently.)

The most practical piece of information and advice is this: Birds don’t have capsaicin receptors, which means that they don’t notice the hot and spicy quality of chili pepper seeds the way that humans and squirrels do, so if you’re having problems with small mammals eating out of your birdfeeders, mix some chili peppers into the feed. The squirrels will hate it – humans are the only mammals who eat peppers on purpose.

People with smaller fingertips are able to perceive finer distinctions because we have the same number of nerves in our fingers, so the smaller fingertips have those nerves in a denser configuration. No matter how sensitive someone might think the sexual organs to be, they don’t have that density of nerve fibers of fingers or lips, which means that if a blind man loses both arms, he’ll be more able to read Braille with his tongue than with his penis. But how many armless blind men are there in the world? A lot of the stories are similarly at the extremes, dealing with odd cases that may only happen once or twice in a lifetime.

With an entire chapter on sex, you might think that there’s some useful and practical tips, but not really. I think it’s interesting that the clitoris actually reaches down and wraps around the vagina (it has wings inside a woman’s body like a butterfly poking its head out), so that even shoving a penis in there can stimulate the right organ, but that’s not going to help me much. I don’t know how many women there are who differentiate between orgasms from touching the clitoris and orgasms from touching the vagina, or how many of them share that Freudian idea that direct clitoral stimulation is less mature or less worthwhile than vaginal intercourse, but Linden explains scientifically why that’s rubbish. An orgasm is pretty great, no matter what part of the body it comes from, so don’t shit on other people’s jouissance.

In a study of pairs of people touching in public, Latin Americans and the French touch dramatically more often than Americans or the British. You can stare at couples in an English coffee shop for an hour without seeing anyone physically touch anyone else. Americans are only marginally better – if you want to see some social touching, head to the Mediterranean (and other places with a strong Mediterranean influence). Similarly, if you want to experience social touch in public, don’t marry an Englishman; find a Latin lover instead.

Imagine that we were vampire bats, and we were close nest mates, either very close friends or family or lovers. One night, I go out hunting and come back full. A meal can last one of us a few days, so I’m ready to hunker down for a long nap. You weren’t in the mood to go out tonight, and now you’re hungry. You might start licking my body, and if I didn’t protest or push you away, you’d move up toward my lips. We’d kiss for a little, and then I’d vomit blood down your throat, because that’s how it works for vampire bats. Tomorrow night, we’ll both go out. Maybe we can share an animal – you can bite it first and lap up the blood that flows out, because we don’t suck it out of the wound, and then I can carry on lapping it up before it clots.

Did you know that vampire bats have infrared temperature sensors that allow them to find blood vessels more easily? Did you know that certain hospitals have similar vein-finding technology, so the phlebotomist can flash a light on your arm and see plainly where all the veins are, to facilitate injections and blood withdrawals? Rattlesnakes also have infrared sensors, but they work at a distance of several feet, much farther than the bats’, and they combine with messages from the eyes to give a more complete picture of the world than we humans can see. Because animals are amazing.

People are amazing too. We sometimes perceive touch when nothing is stimulating the nerves, based on memories and expectations and stimuli that we don’t consciously perceive. It’s nice to know that phantom cell phone vibration is normal (for doctors, which I am not); it’s good to know that sleep paralysis is not an isolated phenomenon, but seeing the actual numbers, it’s not as normal or as common as some other reports have led me to believe. It’s also good to know that no matter how effective machinery can be at stimulating certain parts of the body, it can never fully replace another human’s touch.

I appreciate Linden’s style and approach. He’s writing for a general audience, so the information is kept at a level that someone like me with no specialized training can understand fairly easily. The subject is also discussed in a general way, as an overview of current research that doesn’t go too deep. One of the things that I learned in graduate school is that you can have either breadth or depth, but seldom both. Linden’s breadth on the subject made me think that he might not actually be an expert, and reading the Acknowledgments section, he’s not. He’s a brain researcher, yes, but not a touch specialist. That doesn’t discredit or devalue the book: the research is still good, it’s just that he had a lot of help with that part of it.

I also appreciate the fact that he recognizes where the research runs out – there are several places in the text where he recommends further research and greater experimentation, even where he explains the precise sort of experiments that could be done to test our current theories. There’s still a lot that we don’t know about how touch works and why we perceive things as we do, which means that there’s a lot of work for medical researchers and other scientists to do in this area.

This book is recommended for general readers who are interested in understanding brain function and touch mechanisms, but for medical or nursing students, I’d point you to the notes section and encourage you to go directly to the source materials. You need more practice in reading that sort of text instead of popular nonfiction. I will also say that I am dramatically more interested in the sociology of touch than the physiology, so this wasn’t the best fit for me, but it was good nonetheless.

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Comments
  1. “Don’t shit on other people’s jouissance” should be posted up prominently in many public places. 🙂

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