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Neuroscience-Infused Body Scan

When I first began to practice mindfulness, I loved sitting meditation but struggled with it because I had so much pain in my body. In fact, I had been living with varying degrees of chronic pain since I was a teenager and had tried all kinds of different therapies, to no avail. Doing a lot of sitting meditation didn’t help the constant radiating pain at the back of my ribcage, behind my heart. In fact, sitting seemed to be making it worse. But I found that if I could find the time to practice total relaxation every day, then the pain was somewhat manageable. So I became a total relaxation fanatic, taking every possible opportunity to lie down and do some form of body scan.

…this was practice in the spirit of the charter of the Order of Interbeing, which includes reference to “direct experimentation on the nature of interdependent origination through meditation.”

I tried all kinds of different recordings—from various teachers and traditions—to guide my practice, and I had some favourites, but no matter which recording I used, I noticed I could rarely maintain my concentration from the beginning to the end and not fall asleep. I also noticed that I struggled to follow the common suggestions to send love to such and such a part of your body, or smile to your heart, and so on—and these are phrases we very often hear in Plum Village guided body scans. I found that style of guidance made me frustrated and angry, because I didn’t feel any love for any part of my body—what I felt was mostly rage and pain. It doesn’t mean that that style of guidance is bad or wrong, it was just that I struggled to connect with it—it seemed abstract to me: theoretical, rather than something I could actually feel. Little did I know I was dealing with deeply buried childhood trauma; I still had an awfully long way to go toward creating enough safety in my body to encounter those deep wounds and then to embrace that pain without getting overwhelmed. First I needed to overcome my alienation from my body—I needed to gradually learn to be kind to my body, to feel love and gratitude for my body, and to actually live in my body, rather than only in my head.

So I decided to see if I could figure out my own way of guiding my attention, with the aim of being able to sustain my concentration from the beginning to the end without falling asleep. I was very curious about the order in which we scan the various parts of the body. Suppose you start at the top of your head; what happens when you get to your neck? Do you scan down your arms to your hands? And then what? Do you come back up your arms and then down the trunk of the body? Or do you jump from your fingers, back to the neck, or something else? And do you do one arm at a time, or can you be aware of both? (That’s a surprisingly deep question actually.) The same goes for the legs. I wanted to see if there was a logical way to scan through the whole body without feeling discontinuity somewhere along the way. To me, this was practice in the spirit of the charter of the Order of Interbeing, which includes reference to “direct experimentation on the nature of interdependent origination through meditation.”

In the process of trying to find the best way to restore my connection with my body, I realised that I needed to learn more about the brain. My conviction that this was worth digging into more deeply was only strengthened by Thầy, who said during one of his Dharma talks, “When the ancestral teachers began to teach Manifestation-Only, biology was not developed. In our own time biology has advanced considerably and practitioners should know how to take advantage of the knowledge of biologists in order to understand more about mind [and store] consciousness….They need to learn about the central nervous system, the peripheral nervous system, the behaviour of the neurons and the behaviour of the brain. With these studies [practitioners] will understand the Manifestation-Only teachings more clearly.”

Diagram 1: Cortical homunculus—the somatosensory (white, left) and motor (green, right) strips lie side by side on the cortex. Both strips exist on each hemisphere. Illustration from Spencer Sutton.

Feeling the body map in the brain

I had already learned about the cortical homunculus as a child, but when I revisited it as a meditator, I became quite excited. The cortical homunculus (see diagram 1) refers to one of the main maps of the body within the brain. In order for the body to work, the parts of the brain that govern the movement of the various body parts, as well as receive the sensory signals from those parts, need to be organised in a way that corresponds closely to the way the body is structured in space. Imagine if the part of your brain that controls your left thumb was adjacent with the part of the brain that activates the muscles in your right calf, and if the next bit controlled your left eyebrow, and so on. It would be a real tangle and a total mess in terms of wiring—I’m also not sure that walking or catching a ball would work very well. So rather unsurprisingly, as in the well-known song “Dem Bones”—“…Knee bone connected to the thigh bone, thigh bone connected to the hip bone, hip bone connected to the back bone…”—what is proximate in the body is also proximate in the brain. That sounds more complicated than it is—it just means that the part of your brain that responds to sensory stimuli from the body (for example), is laid out along the surface of the brain in the same way the body is laid out in space. If two parts of the body are close, then the brain areas that govern them will also be close—with the major exception of the midline of the body: the left side of the body is governed by the right side of the brain, and vice-versa, so sensory stimuli arising from either side of the midline of the body end up quite far apart on the body map in the brain. This and other details may turn out to be important in relation to practicing body scan meditation, which is what this is all about!

…thanks to the miraculous energy of mindfulness, we can become aware of what is already going on in our body, which is life itself.

Before we go more deeply into the layout of the cortical homunculus, perhaps it’s worth saying that there are actually multiple body maps in the brain. What you see in diagram 1 are the two primary ones—the first that were discovered, and consequently the most well-known: the motor cortex, which governs the activation of the muscles (movement), and the somatosensory cortex, which receives continuous sensory information from the whole body. In fact, it turns out that there may be four separate parallel body maps in the somatosensory cortex alone, with one dedicated to light touch, one primarily responding to proprioceptive signals (where your limbs are in space relative to each other and to the body, derived from muscle activation information), and the others receiving a mix of inputs—it gets complicated pretty quickly. There are also two separate body maps in the cerebellum, active in maintaining balance, as well as learning and remembering sequenced movements. Deeper within the brain, from the brainstem, to the thalamus, and up to the insular cortex, there are multiple internal body maps relating primarily to feelings, emotions, and motivation, but also to balance and the maintenance of homeostasis. In fact, it may be misleading to think of all these body maps as distinct, separate things (though that does seem to be the dominant tendency); rather, as we learn more about these various body maps, a densely interlinked and interdependent picture is emerging wherein our body maps may not really be separate from each other at all. Since these maps are all interlinked with the body itself, they don’t exist as something separate in the way that a map appears to be separate from the territory it depicts. Our brain maps are actually part of our body. So when you relax your body, or scan your body, are you scanning your body, or are you scanning your brain? Is there actually any difference?

Now that we’ve established that this is a deep, mysterious, and very active area of brain research we can ask the question: “What does this have to do with my suffering and my happiness?” Asking this question allows us to quickly find out whether or not we are wasting our time learning about the cortical homunculus. When I began investigating this, I had started to understand that a large part of my background feeling of unease and discomfort had to do with my inability to dwell happily in my bodily sensations. I had a strong tendency to identify with the little voice in my head, my stream of consciousness narration of my life, and whenever I tried to apply Thầy’s teaching to bring my mind back to my body, most of what I experienced was unpleasant, tense, painful, and unsafe. As a result I didn’t stay in my body very long—maybe less than one second—even if I tried to diligently bring my attention back again and again. At the same time, I had faith in Thầy’s teaching, and was starting to understand that quieting my thinking helped develop my ability to feel, and to stay with my feelings—to be in my body, and to live from there. Learning that the brain’s way of relating to the body is structured in a certain way, I had a strong intuition that this understanding might help me to stay with my body, to develop stability in my mindfulness of bodily sensations—to go from mindfulness to concentration, and who knew, perhaps even to insight.

Stepping back for a moment, it’s really very odd that we can, just by choosing to, be aware of different parts of our body. Our body is there, alive, whether or not we are aware of it. But thanks to the miraculous energy of mindfulness, we can become aware of what is already going on in our body, which is life itself. And we can choose which part of our body to sense into—which part of our body to feel—and then we can learn to sustain that awareness. I don’t know about you, but to me, this is a constant source of wonder and astonishment. So the question I really wanted to find the answer to was this: Given that I can choose to pay attention to all the different parts of my body, is there a particular sequence that my body/brain prefers to follow as I feel into the various parts of my body? 

A neuroscientist may come along and tell me it’s completely wrong, which would make me very happy—I would get to learn something new.

Looking at the cortical homunculus, I started to think about what was going on when I paid attention to my hand, for example. If I choose to notice the sensations in my right hand, I would expect the area of the sensory homunculus on the left side of my brain that corresponds to sensory stimulation of my hand to become (more) active. (I choose to focus on the sensory homunculus rather than the motor homunculus because in body scan meditation we are not moving, or planning to move, but feeling.) I don’t need to provide any particular sensory stimulation in order to feel something because there’s already so much going on; my hand’s sensitivity allows me to feel the tiny movements of the air on my skin. I can feel the sensations of warmth and cold, I can feel the relationships in space of my fingers to each other and to the palm of my hand, I can feel the degree of tension or relaxation in the muscles of the hand and fingers, and I can even feel my pulse in my fingertips.

But there’s another very important piece of information about brain maps that gave me a key idea. Our brain maps are plastic, which just means that they are flexible—they change; they change with training, and they change according to what we are doing. When riding a horse, the horse becomes part of your body map—you become one with the horse. This is also true to some extent when we are using tools—like a mechanic, lying under a car, who “feels” with the end of the wrench even though he can’t see the part he’s working on. The brain maps of musicians’ hands gradually expand with training, taking over neighbouring cortical real estate. 

If the edges of the different parts of my brain map are flexible, they could probably move and merge with nearby areas—in other words, if I’m aware of my hand, then it’s quite likely that that awareness, or brain activation, will “spill” into nearby areas. A more precise formulation of my hypothesis is that when I pay attention to a certain part of my body, the next easiest part of my body to pay attention to would be whichever part of my body is the nearest according to the way the body is laid out in my brain, rather than the nearest body part in physical space. To be clear, this is a hypothesis, and I don’t know for sure that it’s correct. A neuroscientist may come along and tell me it’s completely wrong, which would make me very happy—I would get to learn something new.

Diagram 2: a cartoon representation of the sensory homunculus—note the parts of the body with the most innervation get the most brain real estate. Illustration from Anatomy & Physiology.

The flow of awareness

This is where the details of the cortical homunculus come into play. Most of the parts of the body that are adjacent to each other have brain areas that are also adjacent—but not all. If I imagine brain activity, or my awareness, as a fluid that gradually spills across the surface of the representation of my body in my brain, the flow of this liquid could indicate a “natural” order for a body scan. Looking at the sensory cortex in diagram 2, if you were to start by feeling your tongue, then your awareness would flow to the inside of your mouth, then the lips, the space beneath the nose, the nostrils, the nose, the eyes, the eyebrows, the ears, and forehead, and then…. The thumb! That’s the weird and surprising part—if you follow the somatosensory cortex from the bottom to the top, or from the outside towards the middle of the brain, then your face is mapped from tongue to forehead, or bottom to top, but your body is mapped from top to bottom: neck to feet. And there’s this strange jump—rather than coming gradually down your neck, shoulders, arm, wrist, and hand to the thumb, the brain-map jumps from forehead to thumb. That’s the next place your awareness would flow (if my hypothesis is correct, or partly correct, which, I stress, could well not be the case!). From the thumb, your awareness might tend to spread to the fingers, one by one from index to pinkie, then to the palm, wrist, hand, arm, shoulder, and neck before detouring around the back and top of your scalp, then flowing down the trunk, armpits, chest, upper back, midriff, pelvis (but not the genitals), hip, thigh, knee, calf and shin, ankle, foot, toes, and then the genitals, again with an odd discontinuity.

This would be the scanning order for one side of the body only. If we were to continue sensing down into the middle of the brain and then up the other side of the opposite hemisphere, our scan would continue with the toes of the other side before following the reverse sequence up the other side of the body. Alternatively, we could follow the same sequence, starting at the tongue, but for the other side of the body. (Interestingly, the tongue has both contralateral and ipsilateral representations in the somatosensory cortex, so it may make more sense to start with the whole tongue, even if you’re only going to scan one side of your body.) As you can see, it gets interesting (or complicated, depending on your outlook) pretty quickly.

I prefer to scan both sides of the body simultaneously and to investigate the differences I feel in the qualities of sensation on each side. The main thing, I believe, is to be creative, and to explore; we can find multiple different ways to practice, and then investigate which works best. This, I believe, is what is meant by “direct experimentation on the nature of interdependent origination through meditation.”

Another important thing we can learn from looking at the cartoon image of the sensory-motor strip (diagram 2) is that the sizes of the different brain areas that map different body parts don’t correspond to their actual size, but to how sensitive they are—their degree of innervation. This makes intuitive sense; if a part of your body has relatively few nerve endings, then the brain only needs to devote a small segment of cortical real estate to receive those signals. What does that mean for our body scan? To me, it suggests correlating the time spent scanning each body part to the relative sizes of the brain representations of these body parts (as opposed to the size of the body parts themselves). More simply, it may make sense to spend more time feeling into the more sensitive body parts that have more brain real estate devoted to them—the tongue, the face, the thumbs, and hands (look at how much bigger your thumbs are than the other fingers on the cortical homunculus).

Shining light on the brain-body connection

The more I delve into this area of brain science, the more I realise the situation is vastly more complicated than I first thought. Having started out with the intention to better understand the sensorimotor homunculus, I am now asking myself how much I am really relying on the sensorimotor cortex during body scans. Might I actually be relying just as much on the other, deeper body maps, the ones that convey feelings of proprioception, of warmth and coolness, of pressure and pain? When I’m doing a body scan, which modality of sensation am I most aware of? And how many different modalities am I simultaneously aware of? 

These questions lead to the concept of interoception, defined by neuroscientist Bud Craig as “the sense of the physiological condition of the entire body.”* This is not really one sense, but is multimodal and comprised of “nociceptors, thermoreceptors, osmoreceptors, and metaboreceptors…which innervate every tissue of the body (including bone) and report all aspects of the physiological status by signaling temperature, hypoxia, hypoglycemia, hypo-osmolarity, acidity, interleukin-1-beta, muscle metabolic products…and so on.”* Reading this passage makes me think of the instructions we find in sutras like the Four Establishments of Mindfulness or the Kāyagatāsati Sutta (the same phrase occurs in both): “Further, the practitioner meditates on her very own body from the soles of the feet upwards and then from the hair on top of the head downwards, a body contained inside the skin and full of all the impurities which belong to the body: ‘Here is the hair of the head, the hairs on the body, the nails, teeth, skin, flesh, sinews, bones, bone marrow, kidneys, heart, liver, diaphragm, spleen, lungs, intestines, bowels, excrement, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, mucus, synovial fluid, urine.’” You might think, “How can I possibly be aware of all that?” But the more we discover about our interoceptive capacity, the more it seems that we can in fact sense into pretty much every part of our body.

It is my conviction that our ability to sense what is going on in our body is fundamental to becoming free.

The growing field of research into our interoceptive capacity is shining light on aspects of the brain-body connection that I believe are highly relevant to us as meditators. For example, interoceptive sensitivity is highly variable between people. This can be measured in several ways, the most simple being a test of the accuracy of the self-perception of heart rate. And why should we care? It is my conviction that our ability to sense what is going on in our body is fundamental to becoming free. Free from what? Free from being pushed by our discomfort, by our craving, by feelings about something that happened yesterday that we’ve been ignoring. There has been a tendency for the last few hundred years (in the West, at least) to idealise the (imaginary) notion of purely rational and unemotional decision making. The tendency has been to see emotions as a distorting factor—something that clouds our mind, interfering with our ability to decide—making us irrational and unpredictable. How many times, for example, have powerful groups of men declared that women cannot be trusted with positions of leadership or authority because they are too emotional? According to this outdated, misogynistic, and fallacious view, emotions are a problem to be eradicated so that we can make optimal, unbiased choices. I wonder if this wrong view is one of the roots of our current derangement, violence, and indifference as a society.

Mindfulness of feelings

We have also had the tendency to see emotions as transitory and to only pay attention to strong emotions like rage or fear while overlooking the rest; this tendency has continued to some extent to influence the study of emotion in neuroscience. Fortunately, that paradigm is now being supplanted by a wealth of new evidence suggesting that all our decisions and behaviours are guided by emotion in the form of continuous interoceptive signals in and from the body. According to this new way of seeing, our capacity for reason arises out of our continuous sensing of the state of our body—integrated by the brain into an experiential whole we call emotion—and not in spite of it. This new understanding of interoception leads us to the conclusion that every decision we make arises out of our feelings. We decide based on whether we feel our choice will lead to pleasure or pain, to happiness or to suffering, whether we consciously recognise this or not.

If this is true, we might suppose that those with a more developed interoceptive capacity would tend to make better decisions—if we know how we’re feeling now, we probably have a better chance of knowing how we’re going to feel in the future. And I would suggest that as this ability to know what we’re feeling is refined, we touch the possibility of greater and greater freedom: the ability to say no to negative habits that have brought us into suffering again and again. Research into the characteristics and abilities that correlate with higher interoceptive sensitivity is ongoing, but the results are already striking, as described in the following passage from the Handbook of Emotions in the chapter “Interception and Emotion,” by Bud Craig, 

“Interoceptive awareness correlates with sensitivity to and tolerance for a painful stimulus, with gastric sensitivity, and with self-reports of bodily awareness. An individual’s heartbeat awareness score also correlates with autonomic reactivity, and with self-rated intensity of emotional feelings, whether positive or negative. Further, better heartbeat perceivers are better at reading their own emotional feelings, as well as others’ emotional feelings; they also function better cognitively in tasks of selective and divided attention, and in decision-making tasks based on environmental cues or intuitive choices. They even have a more accurate subjective sense of the passage of time in the range of 8–20 seconds. Importantly, better heartbeat perceivers display better self-regulation of energy expenditure.”*

I believe that the Buddha wanted to make it easy for us—he knew that often when we begin our meditation, our mind will be dispersed and therefore in need of something very, very simple as a way in.

If you’re now wondering how strong your interoceptive sensitivity is, there’s good news, because interoception can be trained. And how should we train it? Well, probably by using it! We need to consciously switch on all of our interoceptive senses—we need to (re)learn how to feel. If we want to be able to feel what we’re feeling, then we need to be in touch with our bodies, because that’s where our feelings are. Mindfulness of the body leads to, and to a large extent already is, mindfulness of the feelings. We need to (re)learn to be an embodied consciousness. I would hypothesise that one way to do this is to practice lots and lots of body scans. If we’re going to do lots of body scans, then it becomes worthwhile to look into the how. For me, it was important to be able to establish concentration and stability of attention throughout the body scan, which is why I explored following the cortical homunculus.

The Sixteen Exercises of Mindful Breathing

But I also took a clue from the Sixteen Exercises of Mindful Breathing, the Ānāpānasati Sutta, which starts with something easy. The first exercise the Buddha invites us to practice is to recognise the in-breath as in-breath, and the out-breath as out-breath. It’s very interesting to me that when I ask practitioners what they actually do on the cushion, most admit that they tend to skip this first exercise—because it seems too easy. They move right away to following the in-breath and the out-breath all the way through. The first exercise is actually much, much easier than that: all you have to do is to know whether you’re breathing in or out. That’s it! I believe that the Buddha wanted to make it easy for us—he knew that often when we begin our meditation, our mind will be dispersed and therefore in need of something very, very simple as a way in. Something simple enough that our scattered mind will be able to do it—something we’ll be able to succeed at. If you immediately start trying to follow your whole breath without any interruption of thought, well… good luck. But if all you have to do is notice whether or not this breath happens to be an in-breath or an out-breath, then you have a chance to get it right, and to get the reward from having succeeded, which allows the mind to become interested, and then to settle and deepen into the next exercise, and so on.

In my efforts to establish concentration during sitting meditation I found this method of starting with something easy to be very effective. I therefore wanted to find something equivalent with which to begin a body scan. What I found was that if I start with a very quick, rough-and-ready scan, I can complete the whole thing and know that I’ve completed it. This creates a little positive feedback, and from there I can do a slightly longer and more “zoomed-in” scan. I usually start with a ten-second scan, roughly following the order of the sensorimotor homunculus: “I have a face, this is the feeling of my face; I have hands, this is the feeling of my hands; I have arms, here are my arms; I have a torso, here’s how my torso feels; here’s my pelvis, here are my legs, and feet, here’s how it feels to have these legs and these feet, and here are the feelings in the genital area.” I do this scan in about the same amount of time it takes to read it. I almost never get distracted or fail to complete that quick and simple cycle. From there my mind is happy to do a slightly longer version, noticing the tongue, the nose, the eyes, the thumbs, the fingers, the hands, and so on. This second cycle takes about thirty seconds. Then my mind starts to settle and become curious, which allows me to zoom in further and to notice more dimensions of sensation. I am now ready to increase the resolution and depth of my sensing, eventually coming to a full body scan that might take as long as thirty or forty minutes to complete. Further stages can follow: scanning the digestive system (which is represented in the cortical homunculus below the tongue, suggesting a natural extension of the body scan), other organs, focussing particularly on the dimension of change, or on (micro)movements in the body—the possibilities are endless. I practice lying down, in the sitting position, while standing, and even while walking—it’s very interesting to become more embodied and relaxed while walking.

…if this approach seems too analytical or technical for you, then just let it go.

So, does it work?

Does following the order of the cortical homunculus make any difference? I invite you to answer that question for yourself by trying it out and comparing your experience with your usual body scan practice. But if this approach seems too analytical or technical for you, then just let it go. The technique is not the main thing. The main thing is to enjoy the practice and for it to be pleasant and easy. We should avoid the tendency to think of practicing body scan meditation in order to get something, or to get somewhere, or to develop something. If that seems to contradict things I said elsewhere in this article then yes, it does. I contradict myself, but being comfortable with apparent contradictions is an important aspect of the art of meditation. The art is to balance a little bit of method and training with a whole lot of letting go and aimlessness. As for me, since using this method I have noticed a steady improvement in my concentration. But is it because this way is better, or is it because I’ve been training myself to practice in this way for almost a decade? Maybe it’s no better for establishing concentration than any other scanning order, and maybe it doesn’t even make neuroscientific sense—I’m very much open to that possibility. I don’t think that this is necessarily the best way to practice body scans, or even that there is a best way, but continuing to explore and investigate nourishes my interest and enthusiasm. I enjoy the practice, and I’ve never yet been bored.

* Craig, A. D. (B.). Interoception and Emotion: A neuroanatomical perspective. In M. Lewis, J. M. Haviland-Jones, & L. F. Barrett (Eds.), Handbook of Emotions (New York, NY: The Guilford Press, 2008), pp. 272-292. 

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What is Mindfulness

Thich Nhat Hanh January 15, 2020

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