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What is Pain?

August 11, 2021

Most people think of pain as a response to injury, when in fact pain is your brain’s evaluation of a threat. It is an experience or output that is felt when a person is in danger. Once your brain has processed all the relevant information about a situation, it decides whether you need to feel pain in order to motivate you to take action against a threat and ultimately keep you out of harm’s way. You can break bones and tear muscles, but you will not experience any pain unless your brain processes that you are in danger. People who are in catastrophic events can experience no pain! Surfers who have had their legs bitten off by a shark or soldiers who have lost a limb in war have reported only feeling a bump at the time, or consider the athlete who fractures a limb while in the final seconds of a game and continues playing without pain. Now consider the last time you had a paper cut and it felt like the WORST pain you had ever experienced. The amount of pain you experience does not necessarily relate to the amount of tissue damage you have sustained.

Pain Depends on Context!

Consider a professional dancer and violinist who both sustain the same injury to their finger, who do you think is likely to experience more pain? The violinist’s identity and livelihood is put at risk due to his finger injury and therefore it poses much a greater threat compared to the dancer (who may experience more pain with a toe injury). In this way, the context of the situation gives meaning to the pain response.

Ignition Cues are environmental sensory cues that can kickstart the pain experience. The brain has labelled these cues as potentially threatening, and therefore the nervous system becomes more sensitive when they are present. 

If someone falls down a flight of stairs and breaks their leg, whenever they see a staircase their brain may change their pain threshold and make their knee more sensitive to pain. Males have been shown to have greater pain thresholds if they are being tested by a female. 

Often when someone is injured at work, their brain may register their workplace as an ignition cue which may exacerbate their symptoms while at the workplace

The Physiology of Pain

You have different sensors spread throughout your body that are all specific to certain types of stimulation (mechanical, temperature, chemical). These sensors carry information about what is happening at the tissue to the spinal cord. Nociceptors are specialized sensors that respond to multiple types of stimuli, however regardless of what the stimulus is, the message is always the same: “DANGER!!!” This danger signal goes up the spinal cord and into the brain, where a complex process happens to evaluate the information. Multiple areas of the brain are consulted, looking at memories, emotional context, consequences, and reasoning before making a decision on the level of threat. If the brain concludes that the threat is real, a pain output is created. Several systems of the body are involved in the expression of this pain output, such as the endocrine, motor, autonomic, and immune systems. There are no pain pathways, pain receptors, or pain centers in the brain. Brain imaging studies have shown that the brain activity of someone experiencing pain is totally different from person to person, although there are clusters of activity in multiple areas of the brain. Pain hijacks areas responsible for sensation, movement, emotions, and memory to express itself. 

Central Sensitization & Chronic/Persistent Pain

The sensors responsible for passing information to the brain work as efficiently as possible. They only live for a couple of days and continue to adapt frequently, changing thresholds and even increasing in number to keep you out of harm. 

more danger = more sensors = more sensitivity = more pain

Our tissues will typically heal within 6-12 weeks, although even after an injury has healed it can still be painful if there is still an excess number of sensors in the area. There are changes that occur in the spinal cord due to the increased number of sensors sending through danger signals to the brain. These changes mean the brain no longer receives accurate information about what is happening at the tissues, but instead the messages are amplified or distorted. The brain is being told there is more danger at the tissues than there actually is. It’s like your car alarm going off when a breeze blows a leaf across its hood, or your home alarm going off when a fly comes in through a window. Increased stress levels, being labelled with a diagnosis, looking at scans, your activity levels, and your beliefs all have an implication on your pain. Certain beliefs are powerful enough to maintain or even exacerbate a pain state. Thoughts such as “I’m in pain so I must be harming my body”, “I can’t do anything until the pain goes away”, “The machine found [insert scary diagnosis] so it must be bad!” These thoughts will further amplify the (already amplified) danger signal coming up the spine. 

Pain Neurotags 

When you have a painful experience in a specific context, the brain stores this information as a neurotag that can be activated if the same stimulation is perceived by the brain in the future. The more often the neurotag is activated, the more efficient the brain becomes at producing a pain response.

 

The Virtual Body

There is a representation of each body part that exists in the brain, known as the virtual body. Individuals experiencing chronic pain may begin to protect painful areas by limiting activity and guarding movement. This results in a “smudged” representation of that specific area of the virtual body in the brain which becomes less defined and more distorted. This contributes to persistent pain because it adds a layer of threat to a body part. For example, if you’ve injured your back and stop moving, adopting a rigid and guarded posture, your brain no longer knows which movements can be pain free; therefore any movement becomes threatening and painful. The more you continue to move, the more you can identify and localise patterns of movement that are painful due to injury and not just sensitisation. By reintroducing movement, either visually or physically, we can stimulate the virtual body in the brain to dissociate movement from the pain neurotag – this is the goal of chronic pain rehabilitation. In some patients, even the smallest of movements can be aggravating, when this is the case, we begin with visual tasks (ie. imagine bending over without performing the movement).

How to Manage Chronic/Persistent Pain

We need to get individuals with persistent pain moving freely again, without activating pain neurotags. By appropriately planning and grading movement, we can reduce pain sensitivity and ultimately decrease pain. The first step in managing someone with chronic pain is to reduce the threat of pain through education – knowledge and understanding of the pain system is the foundation for therapeutic movement. We also must help them to understand the relationship between his or her pain and activity level.

Pacing and Graded Exposure

Graded exposure involves deciding on an activity that you want to get back to (swimming, running, walking, etc.). We can then find a baseline level where you can perform the activity without a flare up (10 minutes of running). If you can’t perform the activity at all, we can break it down into its component parts first (walk before you run). Once we have established this baseline, you can slowly work towards gradually increasing the volume of the activity (add 2 minutes per week of running). 

Debunking Myths about Pain

  • “Hurt = Harm” – If you are hurting more than normal, it does not mean your tissues are being more injured. Recurrent pain is protective in nature and is your brain’s attempt to steer you clear of the threat of injury.
  • “No pain no gain” – we need to move within “tolerable” levels of pain in order to desensitise the nervous system to movement and re-establish proper movement patterns. If movement is too painful it may only further sensitise the tissues to movement.
  • Only moving within a pain free range of motion – This will also further sensitise the body to movement and increase the threat of pain. Again, we need to move into tolerable levels of pain consistently, and as the movement becomes less sensitive it will be easier to move more freely. Learn to take control of your pain! 
References:
Butler, D. S., & Moseley, G. L. (2003). Explain pain. Adelaide: Noigroup Publications.
Image Credits:
https://eastgippslandosteopathy.com.au/wp-content/uploads/2019/05/what-is-pain-egoc.jpg
https://www.bespokephysiotherapy.com.au/new-blog/2018/6/8/part-1-what-is-pain
https://pixels.com/featured/homunculus-map-spencer-sutton.html

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