Imagine you’re out for a run on your favorite hiking trail. An exposed tree root appears in your path. You notice the root too late and accidentally trip over it, falling to the ground and hitting your knee against a nearby rock. Upon impact, pain receptors in your knee send pain signals up to your brain, which causes your knee to “hurt.” This is a classic, straightforward example of how pain works, right?
Although this is the way that nearly all of us learned to think about pain, recent research has revealed that this is not actually the way the process works. The more accurate, updated physiology of pain presents an eye-opening new paradigm with far-reaching implications for how we see and approach the body in therapeutic settings. And interestingly, these new insights about pain are consistent with classic yogic teachings about our innate mind-body connection. In this article, I’ll offer an introduction to this fascinating new science so that we can learn to take a smarter approach to the experience of pain.
In the trail-running example that I described above, pain was created in your knee when it collided with the rock; nerve endings in your knee called nociceptors sensed this pain, and you then felt the knee “hurt.” In this outdated version of the pain process, pain is viewed as an input to the brain.
Let’s now look at the physiology of pain through a more updated lens. Picture yourself on your trail run again. You accidentally trip over the same tree root and fall to the ground, hitting your knee against the same rock. This time, though, those nerve endings in your knee do not actually send “pain” to your brain. Instead, the nociceptors send a warning signal to your brain that something possibly dangerous just happened in your knee. This warning signal is not pain itself—it is simply a message that says “Hey, Brain, something somewhat concerning just happened in the knee. Over and out.”
Let’s now look at the physiology of pain through a more updated lens.
Your brain takes this warning message and weighs it alongside a multitude of other incoming messages it is receiving at the same time, such as what your emotional state is like in the moment, memories of any past experiences that are similar to the one you’re having right now, whether you are located close to the trailhead or very far down the trail, and whether or not other people who could possibly help you are on the trail, etc. In just a fraction of a second, your brain processes all of these messages at once and makes a decision about how dangerous the situation in your knee truly is. Based on this conclusion, your brain will choose whether or not to create a sensation of pain in your knee, and how strong the sensation will be if it votes for pain.
This distinction is very important. In our previous, outdated model, we thought that pain first existed in the knee and then our brain sensed it—pain was an input to the brain. In this new model, however, there is no pain in the physical knee itself; any pain you experience in that spot was put there by the brain as a protective mechanism—a message that signaled for you to not stand on or overload your injured knee, thereby responding to your body’s needs. Another way of saying this is that pain is not an input to the brain, but rather an output from the brain which helps lead the mind and body toward their next steps and decisions.
Let’s expand on our trail-running example to help us understand why this input/output distinction is so meaningful. This time, pretend that you are again running on the trail, but instead of partaking in a pleasant run for exercise, you are running away from an angry, snarling bear. You trip over the same root and hit your knee on the same rock. The danger receptors (nociceptors) in your knee send the same message to your brain that says, “Hey, Brain, something somewhat concerning just happened in the knee. Over and out.” Your brain decides how dangerous this issue in your knee truly is by weighing this nociception message alongside the other situation you are facing at the same time—the bear. Your brain is aware that your knee may have sustained some tissue damage, but it also realizes that an angry, snarling bear is pursuing you at this very moment. If your brain outputs pain to your knee, this might slow you down, increasing the likelihood that you might be caught by the bear, which is a much more dangerous possibility than some simple tissue damage in your knee. Instead, your brain will probably choose to send zero pain to your knee in this moment so that you can get back up and run pain-free to a safe spot. Once you have found safety, it’s quite likely that you might start to feel some pain in your knee, because your brain will have decided that now that your entire life is no longer in danger, it’s time to prioritize the tissue damage in your knee.
As this bear-chase example illustrates, the brain decides to output pain only during contexts in which it determines pain would be an advantageous signal.
Let’s consider one last trail-running example to further our understanding. This time, you’re out on a pleasant run for exercise (no bear involved), but you also happen to be a professional dancer with a very important performance scheduled that evening. When you trip and fall and hit the rock, your brain is aware that the health of your knee is intimately connected with your ability to dance, which is your livelihood and sole means of financial support. Therefore your brain is likely to conclude that this situation in your knee is particularly dangerous, and it might output more pain in your knee than a non-dancer’s brain would in the same situation. In this instance, a dancer and a non-dancer with the same knee injury might feel different levels of pain, determined largely by context.
These examples illustrate that whereas we used to believe that pain was an objective sensation that exists in the tissues of our body, we now understand that pain is a subjective experience and that it is created and moderated entirely by the brain. A helpful way to think about pain is that it is a message your brain sends you as a signal for you to take protective action against a perceived threat.
In the trail-running illustrations we’ve explored thus far, the type of pain involved is acute pain—pain that is the direct result of a recent injury. But when it comes to chronic or persistent pain (pain that lasts longer than three months), the link between pain and actual tissue damage is often very weak. Recent studies have repeatedly shown that many people have significant tissue damage in their bodies—think herniated discs and other damage in their spine; or torn rotator cuffs in their shoulders, etc.—but no associated pain. And conversely, many people who do experience chronic pain in their bodies have no associated tissue damage that can be detected by medical imaging technology like MRIs and CAT scans.
This almost mind-bending realization is the complete opposite of what most of us have learned about the nature of chronic pain. We’ve generally been taught that if something hurts, it’s necessarily because there is an injury or damage in that place. But the new pain paradigm reveals the brain can choose to create pain for any number of reasons, and actual tissue damage is just one of them. Other factors like emotions, stress, memories of past experiences, and quite importantly, our own personal beliefs about our body and pain can all influence the sensations of pain that we experience. For example, consider someone who experiences chronic pain and believes that her pain is the result of tissue damage. This person might adopt an attitude of worry or anxiety with regard to the painful area of her body, and these emotions can influence the brain to create more or continued pain, even though there might be no structural damage in that area whatsoever. And conversely, studies have suggested that simply learning about how pain truly works is often an effective tool in reducing chronic pain.
This almost mind-bending realization is the complete opposite of what most of us have learned about the nature of chronic pain.
This direct connection between our thoughts and our lived experience in our bodies is one of the most profound insights that the new science of pain offers, and it directly supports yogic teachings about the mind-body connection. One of the core intentions of our yoga practice is to quiet our thoughts, which often have emotions like stress, anxiety, or worry associated with them. If we successfully quiet these potentially negative inputs while moving our body in comfortable, pain-free ways during our yoga practice, this can be a recipe for pain reduction, and may explain why many people report a direct connection between practicing yoga and decreased chronic pain.
This new information about the science of pain has far-reaching implications for how we approach the body and mind in therapeutic settings like physical therapy, massage, and some forms of yoga. For example, once we understand that pain and tissue damage do not always correlate, a natural follow-up question might be: Is treating the body’s tissues, then, the most ideal way to treat all pain? Furthermore, if pain is a subjective experience that is created entirely by the brain, then when we do successfully reduce pain, did we actually change the body or did we change the brain? If you’re interested in exploring these and other fascinating lines of inquiry further, I encourage you to consult this list of excellent readings:
Books, by David Butler and Lorimer Moseley
, by Todd Hargrove
, by Greg Lehman
, by Shelly Prosko
, with Neil Pearson