The Predictive Brain and Chronic Pain, Part 1: Rethinking Our Body’s Alarm System
This week’s article marks the first time we will delve into the brain’s role in a whole slew of chronic health conditions that, frankly, we have historically done a pretty crappy job of considering from the perspective of both the mind and the body. And since I have a lot to say on the subject, it also marks our first two-parter!
In my day job, when I’m not hard at work trying to delight audiences with my (hopefully lovable) ramblings about the brain, I am a healthcare scientist. I help develop new therapies and technologies based on our rapidly evolving understanding of how the brain, body, and environment are all complexly woven together. And one topic has reigned supreme in my career thus far: chronic pain.
Chronic pain is often labeled as an “idiopathic” condition, which is a fancy way of saying that doctors aren’t sure what causes it.
Put very simply, the traditional explanation of pain is that it is a specialized reaction that only occurs when special nerves in our bodies (which are called nociceptors) send signals to our brains as a result of damage to the tissues in our bodies. And this is still the way that most doctors are trained about how pain works today (Fun fact: because of all of the information they have to learn about so many things, the average physician in the United States receives less educational training on the science of pain than a veterinarian).
Upon examination, the vast majority of chronic pain (which is medically defined as pain that lasts more than three months) occurs without a clear source of damage in the body.
Sure, we often hear that chronic back pain (the most common form of chronic pain) is the result of things like disc herniations or spinal degeneration, but the truth is, MRI studies have consistently found that people who have no pain at all have the same number of spinal issues as people who do have pain.
From what the evidence suggests, these spinal imperfections seem to just be another form of normal aging, sort of like wrinkles in our skin. But wrinkles don’t hurt, so what’s the deal? Well, my more loyal readers may already have identified an issue with the traditional explanation of pain as a reaction to damage…
The Predictive Brain
As I will remind you approximately eleventy billion times over the course of our adventures together, the brain does not react — it predicts. If we waited for our neurons to fire only after our brains received and processed sensory data, we’d have gone extinct long ago and the world would currently be ruled by dolphins.
Our brains are designed to start firing automatic responses based on what they predict will happen next. These predictions are tuned constantly over our lifetimes based on the actual sensory data we receive (for more details, check out this article I published about the predictive brain).
I often talk about sensory data as coming from our environment, but it is important to note that a ton of our sensory information comes from inside our bodies, as well. In fact, we have a whole sense dedicated to feeling our insides — it’s called interoception. Just like we use other sensory signals, like sights, sounds, smells, etc., to predict and automatically respond to the things that happen around us, we use interoceptive signals to predict and automatically respond to what goes on inside of us.
For an estimated 80–85 percent of chronic pain patients, issues related to these interoceptive predictions are the actual root cause of chronic pain.
Our Immune Response is More Complex Than You Think
Before we jump into the relationship between interoception and pain, let me take a moment to update your notions of your immune system. You probably learned that your immune system comprises all the white blood cells and other stuff in your body that help fight off infections, right? Well, that is true, but it is only one small piece of the human body’s complex defense system. In reality, we use our whole body (and mind) to first identify and then neutralize threats. Usually we respond to threats in one of three ways: fighting them, fleeing from them, or freezing until they go away. Humans have a pretty impressive array of responses that facilitate these different strategies — from autonomic changes in the body to behaviors we take to control our environment.
Pain is a big part of this complex defense network, and more specifically, you can think of it as our body’s alarm system. When that alarm goes off, we instinctively tend to stop in our tracks and focus on the pain. Where is it? What is wrong? How bad is it?
This is all well and good when something in our body is physically damaged — you don’t want to go running off on a broken leg. Pain occurs as a way to force you to stop and heal, minimizing the long-term impacts of an injury. But most people suffering from chronic pain don’t have a clear injury to point to. In other words, chronic pain seems to be a false alarm. How do you know when it’s safe to move again when there’s no clear injury that needs to heal?
Pain Can Be a Learned Response
Just like all the other autonomic functions of your body — your heartbeat, your breath, your blood pressure — pain is activated automatically by your brain. And contrary to popular belief, it also occurs entirely within your brain. Pain might be triggered by sensory signals from the body, but it always starts and ends with your brain. In a simple injury, nociceptors carry signals from the damaged tissue up through the spinal cord into the thalamus (which is sort of like a big terminal that relays signals to all the different parts of your brain). From there is goes to higher brain regions, like the somatosensory cortex, where you process all your various “touch” and “feel” sensory data. The somatosensory cortex determines the intensity and location of the damage. Of course, at this point, the signals that go to your somatosensory cortex are just being used to confirm or adjust the predictions your brain has already put into action. This is why you immediately feel very real pain when you think you’ve hurt yourself, but it usually goes away once your sensory signals catch up and you realize that it was just a close call — phew!
The thalamus also relays pain signals to the amygdala and anterior cingulate cortex (or the ACC, for short). These parts of the brain deal with threats and emotional processing. When they get involved, things can get complicated. It is the amygdala and the ACC that cause us to perceive pain as unpleasant, and they also contribute to our fears around pain. The amygdala is also highly connected to the hippocampus, the region of the brain that forms our memories. The hippocampus absorbs all the contextual information about what is happening during the painful experience; this includes sensory details from what is around us, as well as interoceptive details from within our bodies. It stores all these details as memories. These emotionally-charged memories form the foundation for our brain’s predictions, and all those contextual details become triggers for future automatic responses.
Now sometimes those details noted by the hippocampus become so closely associated with pain that they can elicit a pain response in the brain all by themselves. This process is exactly like Pavlov’s experiment with the dogs that you learned about in school, only instead of an automatic salivation response that is triggered at the sound of a bell, the brain triggers a predictive pain response at some other cue. For many people, these sensory cues are totally harmless interoceptive signals (stiffness in the back after sitting, tightness in a shoulder muscle that is not frequently moved, etc.), although sometimes they are environmental cues (going to a high-stress job, spending time with a toxic person, etc.). These cues form such strong associations to pain in our brains that they cause the brain to trigger an automatic pain response in anticipation of the injury or damage we expect to occur, even when our bodies are totally fine.
It is extremely important to understand that this process creates very real pain — the same exact pain response you have for any other type of injury — even though the body is undamaged. Pain exists completely in our brains no matter what the circumstances, and the distress that pain causes, even in the absence of damage, is most certainly not “all in your head”. People who experience pain in this top-down manner need relief, but frequently are unable to get it because our current medical system only knows how to treat bodily damage, not pain that’s run amok. But a whole new generation of chronic pain therapies, which target the brain rather than the body, are starting to emerge…
And that, gentle reader, is where I will leave you this week. Be sure to tune in next week where we will talk more about how these predictive pain responses are learned, and more importantly, how they can be unlearned to help find relief.
Diving Deeper
If you are curious to learn more about how the brain creates the same exact pain responses whether the body has been damaged or the brain just predicts that it will be damaged, check out “The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science” by Norman Doidge. This is a great read that explains the mechanics of how the brain can substantially change our experience of the world based on issues related to our neural connections. More importantly, Doidge offers examples of folks who have found a way to use the neuroplastic ability of our brains to rewire in order to recover from a wide variety of brain-based conditions. And in the next installment, I’ll provide some additional resources with specific tools for retraining a hyperactive pain response.
Call to Action
Do you find this perspective on chronic pain enlightening? Has it reshaped your understanding of pain and the body’s response system? Share your thoughts, stories, and insights with us. Let’s foster a community where knowledge leads to empathy, and understanding paves the way for healing. And stay tuned for Part 2, where we’ll delve into groundbreaking therapies that promise not just relief but a transformation of how our medical system uses the interaction of the brain and body to resolve a chronic condition. Your journey towards understanding and possibly even redefining your own pain starts here. Share this conversation, engage in dialogue, and let’s explore the power of our brains together!
