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What you don’t know about pain could be making you worse!

What do you know about pain?

It’s quite likely that your understanding of pain is based on the model first proposed by Rene Descartes over 300 years ago. In it a painful stimulus is detected by a special pain receptor and the stimulus is carried upon a nerve to the brain where you feel pain. Descartes described them as tubes that carried the “animal spirit.” We’ve come a long way, but we still have a lot to learn.

What’s the problem? Well, this model supposes that there needs to be a pain signal and that it has to reach the brain via nerves in order to feel pain. Without a harmful stimulus or a nerve to carry it there would be no pain. This simplistic and mechanistic idea is the basis for most of the treatments developed for pain relief. So we ought to be able to stop the pain by using a medication that blocks the pain signal, but that doesn’t always work. Or we ought to be able to stop the pain signal from ever reaching the brain by cutting the nerves, but that doesn’t always work either. And people with an amputated limb shouldn’t be able to have pain in a limb that no longer exists, but roughly 40% do!

Decades of research have made us realize that Descartes’ theory of pain is woefully elementary and that pain is vastly more complex. According to Dr. Lorimer Moseley, a pre-eminent pain researcher, one thing we’re sure of is,

“100% of the time, pain is a construct of the brain.”

We need to tread carefully here. We are NOT saying the pain is in your head, fake, made up, or a psychological issue. We are saying that pain is a perception created by the brain, just like any other sensation we perceive, whether it is sight, sound, smell, or taste.

If you are experiencing pain it is vital for you to understand how pain works. Doing so can have an immediate positive effect on your pain and associated fear-related behaviors you’ve likely adopted. Therapy for all manner of painful musculoskeletal conditions begins with this first step, so without further ado…

How does the brain create pain?

The brain wants to know when its body is under threat so it can react and protect its body. Clearly this is important for our survival. For this reason, we have an alarm system of ~45 miles of nerves that exist to transmit information from the outside world to the central nervous system (brain and spinal cord) for processing and interpretation.

The first stop for a signal coming from most parts of the body (except the face and some organs) is the spinal cord. There the nerve from the body ends and meets an interneuron, which is like a relay or a gate that can let the signal past or not. The interneuron connects to a second order neuron that carries the signal the rest of the way to the brain for processing.

Cross section of spinal cord with depiction of nerves going to and from

It’s important to note there’s nothing encoded in these nerve signals. It’s merely electrical charge. It is the brain and spinal cord where these millions and billions of electrical charge “signals” undergo processing and get interpreted into meaningful things like vision or taste. However, there are special types of nerves called nociceptors that developed to carry a ‘danger’ signal to the central nervous system (CNS). Signals from these nociceptors have particular significance to the CNS.

Once the signal reaches the brain a dazzling series of nearly instantaneous and subconscious processing steps occur that use many different parts of the brain, and the signal is interpreted and given meaning based on many different things. Things like: How intense is the signal? What mood am I in right now? Have I ever felt this before? Is this signal coming from a body part that’s really important to me? How scary is this? Is this message important right now?

After all of this processing the brain makes a simple decision: is this signal threatening or not? If it’s not threatening you may not perceive anything or you may perceive some sensation other than pain. But, if the brain decides that the signal it’s receiving is threatening and requires protective action then your protective alarm will go off and you will perceive PAIN.


Photo from Therapeutic Neuroscience Education

Most of the time after the threat has passed the alarm turns off and the pain will go away. Sometimes the alarm will stay extra sensitive like after an injury occurs. This makes perfect sense. If tissue needs to heal then your nervous system will respond by creating pain whenever you stress it in order to make you move less and protect the healing tissue. As the tissue gets stronger the protective pain is no longer needed and it goes away.

That’s if everything goes right, but in about 1 in 4 people pain will persist long after an injury has healed. For others pain will come on without any injury at all.

Let’s look at various parts of your nervous system and see what can happen to create persistent, disproportionate, or unexplained pains.

Nerves and ion channels

Nerves send signals, a.k.a. action potentials, when the inside of the nerve reaches a certain charge. They must reach that charge to fire and when they reach that charge they will always fire. There is no half-firing. It’s called the “All or None” principle.

Nerve either reaches threshold charge and fires an action potential or does not. No middle ground.

They reach their firing threshold charge by allowing ions on the outside of the nerve to get inside and those ions do it through ion channels that dot the cell membrane of the nerve. There are many different types of ion channels that open or close in response to various stimuli. Some open with particular chemicals like stress hormones, some open with mechanical stimuli like tension or pressure, some open with temperature changes, some open with immune system chemicals, some open with light, etc. The more ion channels there are that are open the more likely the nerve is to fire.

Depiction of ion channels in nerve’s cell membrane. Can open in response to various stimuli.

The half-life of an ion channel is about 48 hours and, importantly, the type and number of ion channels can change in response to the environment or the brain’s interpretation of the environment. Therefore, faced with a situation where movement is threatening—say after a car crash or a recent ankle injury—the mechanically-stimulated ion channels may increase in number, making the area more sensitive to movement.

Basically, with so many mechanical ion channels present on the nerves, movements are likely to open enough channels that enough ions will flow in and the nerves reach the threshold for firing. This also sheds some light on why you may experience more pain when sick (the immune ion channels are open due to presence of immune system chemicals) or when you’re cold (the temperature ion channels are open) because the open ion channels have allowed the nerve charge to change so that it is much closer to it’s firing threshold, thus more sensitive.

Additionally, ion channels can only be present on the bare parts of a nerve’s cell membrane. Wherever the nerve has its insulation—called the myelin sheath—there will be no ion channels. Ligament sprains or surgery, for example, can injure nearby nerves and remove some of the myelin, which creates new areas for ion channels to form, increasing the sensitivity of the nerve. Also, some inflammatory chemicals are known to strip away myelin, including ones released when a vertebral disc is injured. When a disc is herniated, nearby nerves may lose some of their insulation and gain new ion channels.

Depiction of a nerve showing ion channels on unmyelinated areas

Bottom Line: The more of a particular type of ion channel a nerve has, the more likely it is to fire in the presence of that stimulus. The number and type of ion channels can change based on the brain’s interpretation of the environment. Nerves near an injured tissue can have space for more ion channels, thus they can be more sensitive.

Changes at the spinal cord level

A peripheral nerve is one that originates outside the brain and spinal cord and carries a signal from some body part to the spinal cord. It will enter the spinal cord at a particular level specific to where to where it came from. For instance, if the nerve is coming from your thumb it will probably enter at the C6 level, between your 5th and 6th neck bones.

Recall that it meets an interneuron there. The interneuron can stop the signal there or allow it to pass to a second order neuron that takes the signal to the brain for more processing. When the interneuron is constantly barraged from a specific nociceptor, called a C-fiber, it can die after some time. Therefore an important gatekeeper is removed from the pathway and the signal can proceed to the brain easier, which is one way that persistent pain may come about.

The brain will want to know about this danger signal in order to respond correctly and protect you, so changes can then happen to the second order neuron that carries the signal from the spinal cord to the brain. These neurons can become more sensitive and the receptors can change to remain open longer so that danger signals are relayed more easily to the brain.

Despite all these changes the brain has strategies to prevent unnecessary or irrelevant information from bothering it. Your clothes are constantly stimulating the light touch receptors in your skin and sending signals the to spinal cord, but these signals aren’t important to you most of the time. Think about it. Would you want to feel your clothes all the time? No. So, in a process called descending inhibition, the brain releases numerous chemicals that stop the signal in the spinal cord from reaching it.

Nerve signal going to spinal cord then brain. Brain decides if it’s a threat and amplifies or inhibits the signal accordingly.

Now, if you’re getting constant danger signals coming to the CNS at that level, the brain may do an interesting thing. Assuming that there is a problem there that needs attention, the brain will want more information, much like a CEO concerned about the performance of one of his or her departments will want frequent status reports. Remember it’s trying to protect you. So instead of inhibiting the signal with descending inhibition, it decreases the chemicals in order to allow all those messages through. Now the area is very sensitive to many different kinds of signals like movement, light touch, and temperature that increase the likelihood that they’ll get interpreted as threatening and painful.

Lastly, the spinal cord is not so neat and tidy and compartmentalized as you may think. The nerves sending danger signals from your right low back may be entering the spinal cord at the L4 level. But there are also a few nerves from that painful spot that extend into the L5 level below and L3 level above. A few of those nerves even go to the L4 level on the left side. Now the brain is getting danger signals from parts of the spinal cord associated with areas above, below, and on the opposite side of your painful spot and it may perceive there’s a threat there, too. This should help you start to understand why pain that was once localized starts to feel like it’s spreading up and down and across.

Bottom line: Persistent pain can cause changes in the spinal cord that allow more danger signals to make it to the brain. The brain may decide it needs to pay attention to these signals and stop its descending inhibition and instead amplify the signals. Because the spinal cord is not perfectly compartmentalized the brain may start to perceive that danger signals are coming from areas adjacent to the original area.

Your brain: where perception becomes your reality

The last stop for that danger signal is your brain, where it is given meaning and context and interpretation and you will either perceive it or not. Remember, at this point the signal is only an electrical charge. It has no meaning. It is not pain yet. But it can become that.

One area for processing is the primary sensory cortex. Every part of your body is represented here like a little map of you, with distinct areas for each body part. There is a clump of neurons representing your fifth toe, another representing the top of your head, and another representing your elbow. That’s why it’s possible for a brain surgeon to physically stimulate the area for your thumb and you feel that something is touching your thumb.

Cross section of the brain showing the sensory map. Each body part is represented by a discrete area.

This sensory map is very adaptable and can change based on pain, body part use, etc. For instance, when a person loses their right lower leg that area of the map is no longer stimulated. It’s wasted space. Our efficient bodies hate wasted space so the body parts represented in the areas adjacent to it start to take over. The area for the fingers and thumb are larger in a violinist who has used her fingers for precision activities for years than it is in, say, a bus driver. And the area for a body part that has had persistent pain starts to be “smudged” and less defined than it should be. The result is that there can be processing errors resulting in vague pain, pain that spreads to adjacent areas, and pain when there shouldn’t be pain. “Garbage in, garbage out,” as they say.

Even though we have this sensory cortex there is no single pain center in the brain. Every danger signal makes it’s way to numerous parts of the brain for processing: the sensory map area, the area for emotions, the area for memory, the area for cognition, the area for movement planning, the area for stress response, etc. This complex interaction of areas for pain results in a specific pattern of brain activation for that pain called the pain “neurotag”.

Photo Credit: Zac Cupples

There are neurotags for many other brain activities like throwing a baseball, the memory of your best friend, the smell of chocolate chip cookies, etc. When you do a painful movement that particular movement neurotag will activate and that particular pain neurotag will activate. It is said that “nerves that fire together, wire together,” and this is true. The more that these two neurotags are activated together the stronger the connection becomes. The brain forms a bad habit in a way so that even when the once-injured tissue is healed and no longer needs pain to protect it the movement still activates pain.

Bottom line: The brain is plastic and constantly changing and updating, forming new connections and disintegrating old, unused ones. Nothing that we perceive is uni-dimensional or purely objective. Every signal that the brain receives is processed in numerous areas and affected by cognitions, emotions, memories, anticipation, stress, etc. Therefore, the perception of pain is contextual and can be initiated or changed based on illness, stress, current and past emotions, past memories and more. Feelings of pain can come on without tissue damage. Conversely, you can be pain-free even if you have signs of tissue pathology like tears, arthritis, or degeneration.

So there is a quick and dirty primer about pain as we understand it today. There are volumes written about it and more research being added everyday. Hopefully what you’ve gleaned is that pain is not as simple as: tissue damage = pain.

Back to the title of this blog. How can not knowing about pain make it worse? Simply this: if you believe that your pain is coming on because you’re damaging tissue then you will naturally be afraid to move and you will avoid painful things because you don’t want to cause further damage. These “fear avoidance” behaviors, lack of movement, and cessation of meaningful activities strengthen the idea that there is a threat present. Remember the brain creates pain as a response to a perceived threat. In effect, not understanding pain is strengthening the perception of threat, and ultimately perpetuating your pain. Furthermore, believing that you are damaged and hurting yourself further is just one more source of stress, and stress is well-known contributor to overall pain.

The first step is to remove the conscious threat of pain. This in itself will not make your pain go away. Wouldn’t it be nice if we could all think our way out of pain? But the strength and confidence such realizations give you can start to turn the tide against your pain as you increase your activity and stress your tissues incrementally in a meaningful way. As you do activities without fear, even if they hurt a little, your pain alarm will become progressively less sensitive and you will be able to do more things without setting it off.

There are two paths when you have pain. Which one would you rather take?

Fear and misunderstanding of pain can lead to a cycle of continued pain and disability.

We encourage further reading on this complex topic. Here are some really good articles: