How Does Pain Work? Why It Hurts, and Why It Can Change

This blog is going to attempt to make the complexity of pain more accessible. It's not intended to be a complete encyclopaedia of chronic pain so if there are things that are not covered here or that you think should be included - please let me know (info@biggerthanpain.com) and I will review and amend as appropriate. Let's dive in.

Here's something that surprises most people. If a surgeon opened up the area that hurts the most in your body, nobody on the planet (surgeon included) could point at something inside your body and say "yep, there's the pain". It's simply not possible.

They'd find tissues, and maybe changes in those tissues, but not pain itself. Pain is something you experience. It's real and it's felt wherever you feel it and it's 100% produced by your nervous system. One of the reasons anaesthetics work so well is because we dim down the lights on the nervous system's conscious perceptive systems and feedback loops (in the case of local anaesthetic) not because we massively improve or change your tissues at the time the anaesthetic goes in.

Your nervous system's primal instinctive job is to keep you alive. It takes in information from your body's internal and external environments, processes it, references your previous experiences and many other things, predicts what might happen, and responds. Pain is potentially part of that response.

Nociception is not pain

In your journey to help yourself with pain, you may have come across the term nociception. It looks like a fancy word that you likely don't need to know to make progress with pain - but there is value in understanding how it helps us differentiate some things so let's explain it simply.

Your tissues have nerve endings that send signals about actual or potential harm to the tissues. These nerve endings cover a wide range of potential stimuli including (hot/cold, tickle/itch, sharp stabbing sensations, crude touch on the skin and more). We call those nociceptive nerve endings. The process by which they inform the brain about those signals from our tissues is called nociception ("noci" from the Latin for harm).

For example: I roll my ankle stepping off the footpath onto the road. Those nerve endings fire much more than usual, the signals travel up to my spinal cord and on to my brain, and my brain decides what that means.

Nociception is the message. Pain is one possible response to it. Nociception is one strong influence on pain but it is not pain itself.

Think of someone badly injured in a car crash who feels very little pain until they're safe in hospital. The signals are there, they begin bombarding the central nervous system immediately after injury but in that moment the brain has more urgent priorities. And the reverse is true too: you can have pain with very little coming from the tissues at all, because your nervous system judges that you need protection in that moment (for whatever reason).

In Does focusing on pain make it worse? we spoke about how your own internal pharmacy was able to pump out pain reducing compounds called endogenous opioids when we are fully distracted by something. The car crash example is a much more extreme example of this where adrenaline, opioid production and context can eliminate pain until some parts of that change - like arriving in the safe environment of the hospital.

We also have other signalling systems like the nociceptive system called the mechanoreceptive system (relating to all mechanical type signals to do with movement such as stretch, vibration, pressure, joint position sense) and chemoreceptive (relating to stuff like your blood pH, blood sugar levels, hormones and so on).

This stuff can get geeky and complex so don't worry too much about that if it seems a bit much, it gets easier as we proceed.

The brain's Grand Central Station

When those signals reach the brain, one of the first stops is the thalamus. I think of it as Grand Central Station in New York: a hub where lots of train lines meet. (In reality the thalamus is only a part of the brain and the brain is more like many, many connected Grand Central Stations that each have their own lines coming into and leaving from it).

From there, areas involved in memory, perception of threat, emotion and your stress response all get a say. Your brain weighs all of that up and decides how much protection you need and it will respond using any combination of a pain experience, adapted muscle tone, physiological responses like hormone changes or stress responses and potentially quite a few more.¹

I have put this prediction process into a framework format that you can have a look at here: the Bigger Than Pain Systems Model. The BTPSM is the framework that the whole BTP platform works from.

When the smoke alarm gets more sensitive

So what happens when pain becomes chronic then? When pain goes on for a long time, the nervous system can become more "sensitive". Pain researchers call this central sensitisation. Central meaning that it's happening at the level of the brain and spinal cord, and sensitisation meaning that the thresholds to trigger off some of these responses are more easily met.

The signalling systems don't really change in central sensitisation - the interpretation of those signals does. And that interpretation change predisposes you towards more pain experiences - which is obviously not what we want. Pain can spread or linger beyond the original area. It's a bit like a smoke alarm that used to only go off for a fire and now goes off when you make toast. Not ideal if you like toast!²

The learning effect, memory & repetition

I also like to think of this like a learning effect - except the nervous system is learning in the wrong direction. When pain experiences are regular - they can unfortunately reinforce that you need protection and the repetition of these strengthens that reinforcement. Brains learn more readily from negative experiences than positive experiences because a negative experience typically has some survival value in it.

If I were to touch a piping hot cooker top and badly burn my skin, there is inherent survival value in me learning that touching hot things causes tissue to get injured. Otherwise I would get home from the hospital and potentially do the exact same thing again! So our clever brains choose to learn from these events to prevent future harm.

It's also well supported that adding negative emotion to an experience can write that experience into long term memory more easily and more robustly. Pain that persists can therefore feed your own prediction system the type of experience that can lead to more pain aka a vicious cycle.

(That might read heavily for you. Like it's a vicious cycle that is hard to escape from. For some people, it can be. And despite all of that, I have also seen many hundreds and hundreds of people overcome this cycle with time, unlearning, relearning, evidence of safety building and support along the way.)

Your injury history

If I've rolled my ankle before and it kept me out of football for weeks and made me a miserable old sod, my brain remembers - we established that above. If I were to roll my ankle again, the same sprain carries more threat, because last time it really didn't go well. Previous injuries, how they affected you and what they meant for your life have the potential to shape how your nervous system perceives what is happening now.

A large part of the success of many of my clients is when we can offer their bodies experiential evidence of safety during movement. What I mean by that is that it's all well and good understanding that I've rolled my ankle a while ago, and I know that enough time has passed for the tissue to heal and that I psychologically can understand that it's no longer injured. That's easy to understand.

But it's not the same as actually giving your brain a movement experience that demonstrates that the tissues can tolerate the loads, forces and positions that you avoided while it was injured. Or for someone with persistent symptoms where there is no injury present anymore (or maybe there hasn't been any identifiable issue in your tissues ever) - that experiential evidence is directly disrupting the brain's current prediction for how much protection you need. And that's a damn important thing in my opinion. That's learning in the right direction for the nervous system. Where we build up evidence that we are safe again.

Your beliefs are like the lenses in your glasses

Leaving movement behind for a moment, we flip to the psychological part of a pain experience. This section will by no means cover all of this but we will focus in on a very important influence on pain - the beliefs we hold as true. Beliefs shape the world you see. Picture two people of the same strength, lifting the same box. If one person believes their back is fragile and their spine is crumbling and the other believes their back is strong and adaptable - their beliefs are likely to colour their experience in very different ways. The first is far more likely to feel threat, to adapt their movement strategy and potentially even feel pain - regardless of what their spine actually looks like.

And with the crazy amount of information flying around the world these days through social media, AI and Dr. Google - a lot more people are being exposed to a lot more unhelpful beliefs than ever before.

Research even suggests that the words used to describe a scan can affect how people feel. In one study, people with recent back pain who were given their MRI results reported lower wellbeing six weeks later than those who weren't, even though their recovery in pain and function was similar.³ Words matter. They often shape beliefs about our body and our capability. Handle them carefully.

Your attention

Pain is designed to grab your attention, and focusing on a painful area can influence your pain experience. And there's nuance attached to this so rather than dive deeply here - I've written a whole article on this topic: Does focusing on pain make it worse?

Your emotions and stress

Pain almost always comes with emotion: fear, worry, frustration, sadness. Those feelings feed into your stress systems, which can tip those prediction systems towards the production of a pain experience. If I'm a bit worried about my neck pain, I'll have one experience. If I'm terrified and panicking about the same neck pain, I'll have a very different one. The tissues haven't changed. The emotion has likely meant that the perceived level of threat has.

And I don't want you to think the above emotions piece is me diving into the woo about trapped emotions or anything like that. It's not. It's a recognition that all parts of your human experience have the potential to influence pain. What goes on in your life matters too. If you were to lose your job, sleep badly for a week or go through a hard personal circumstance - all of these things could potentially trigger off a flare up of pain - even with no new or existing injury being present. More on that in Why does chronic pain flare when life gets stressful?

What you've learned to do

When something hurts, we adapt. "I don't hoover any more because it kills my back." "I can't squat in the gym anymore because of my back so I avoid the weights and I just walk on the treadmill instead." Those changes make sense at the time. But in my clinic I often see them hang around for far too long after they're needed - usually without the person noticing. I have long suspected that the adaptations we make (consciously or unconsciously) can actually become factors that maintain the painful problems that people face. If we still move in an adapted way (as an example) - does that confirm the prediction that the adapted way of moving was needed and was the correct response? (My own mind boggles too when attempting to answer that question!)

This is my favourite way to explain what to actually do about all of this.

Think of it like this. For every pain experience, injury, scary diagnosis, bad night's sleep or flare up of pain - imagine you add a Lego block to a Lego house. That house represents THREAT.

For people with persistent pain, their Lego house is usually already well built. For some people that might feel like a mansion or a skyscraper! And not only is that an ongoing build for some people, it becomes a point of reference for your nervous system to check against because it becomes evidence that you need protection. Talk about a double edged sword!

Next to the Lego house of threat is another house, or maybe for some it is a building site. The foundations are there, a few half-built walls and maybe a few doors have been hung. That represents the Lego house of SAFETY.

The task facing a person with persistent pain is simple to describe and often not easy to do without support:

Our nervous systems are biased towards remembering threat, so the threat house is quicker to build. That means safety needs adding consistently, little and often. We are back to that evidence of safety thing I keep bringing up.

Blocks for the house of safety can include:

• understanding your pain more accurately (usually the best place to start)⁴
• movement that feels safe, built up gradually
• walking, strength training, stretching
• better and more sleep
• time with people, and things that are fun
• calming your stress response
• treatment that helps, used as one block among many rather than the whole house
• regaining agency or control over your symptoms

As the saying goes - principles are few, methods are many. A good hands-on session might add a few safety blocks and that's great. It likely won't build the house for you though. What you do in the rest of your week matters more.

Hopefully this has helped you understand a bit more about how pain "works", how it is influenced and how we can begin to work towards some improvement in how we manage and potentially overcome it. If you'd like to get a bit more clarity on what might be influencing your pain, our free Clarity Report is a great starting point. If you want to actively start working on your pain, the BTP app has a 14-day free trial (card required - cancel anytime).

This article is general education, not a diagnosis or a substitute for care from your GP or healthcare team. If your pain is new, getting worse, or comes with symptoms that worry you, please get it checked.

I'm building Bigger Than Pain in public. Follow along in Building BTP.