Chronic Pain Pain

Can chronic pain be a learned response?

Chronic pain pain can be a frustrating experience. Usually there is either no specific injury to cause the pain or the pain lingers long passed the original injury. But why would pain occur after an injury or without an injury at all? This blog post will discuss how inaccurate memories could lead to chronic pain and how pain can become a learned response.

First, let’s talk about Pavlov’s dog. In the famous experiment, Pavlov would ring a bell every time a dog was to be fed and the dog would begin to salivate. The dog had learned that when he heard the bell ring, he would be eating soon. Pavlov would then ring the bell without feeding the dog and the dog would still salivate.

This is a classic example of associative learning. The dog associated the ringing of a bell (a conditioned stimulus) with feeding and would salivate even with the food was not present (a conditioned response). Normally the dog would salivate when food is present (an unconditioned response) but not when he heard a bell.

This process of associative learning may also be involved with chronic pain. Whenever you suffer an injury, your brain takes a mental note of what was occurring to prevent you from suffering the same injury in the future. Your brain takes all of these details from the injury (what movement you were performing, what weight you were lifting, where you were, etc…) and stores these as neurotags in the brain. When you are in similar situations in the future, they trigger these neurotags to make sure that you are cautious and everything is okay. This process is a normal occurrence and is usually not sufficient to cause pain.

However, problems can arise when the encoding of these neurotags becomes faulty. Instead of the neurotag being stored as a crisp, detailed image, the neurotag can become blurred making it difficult for your brain to decipher the exact details. The blurred neurotags then cause the brain to pair similar movements and situations to the original injury. This is referred to as stimulus generalization.

Stimulus generalization allows the brain to activate the neurotags without the original stimulus. The activation of these neurotags becomes a conditioned response meaning it has been learned. In the Pavlov experiment, ringing the bell without the presence of food is sufficient to stimulate salivation in the dog. Similarly with chronic pain, the original stimulus is no longer need to generate pain and can be triggered by other stimuli.

For example, let’s pretend that you are lifting heavy weights at the gym. You grab the 35 pound kettlebell and start to perform some deadlifts. Then suddenly you feel a localized sharp pain in your lower back. You immediately stop lifting and decide to take a little time off of lifting to let the tissues heal. The memory of the injury could be represented by this image.

Original injury with 35 lb kettlebell

A few months pass, but the lower back pain persists. It used to only be an issue when you were picking something heavy off of the ground, but now it seems that anytime you bend your lower back you have pain. In this case, the memory of the injury was blurred making it difficult for your brain to determine if you are putting yourself in the same situation that you were injured in.

Which of the photos shows the original injury with the 35 lb kettlebell?

Since the brain cannot determine if you are replicating the original mechanism of injury, your brain produces pain because the brain believes you are in danger. While the brain is trying to protect you and your tissues, it has become overprotective. The goal of treatment for these chronic pain cases would be to revise the neurotags so the brain can decipher which movements are dangerous.

The green image was the original injury.

The reason why the encoding process can create a blurry neurotag of the injury is unclear. This process is meant to be a protective mechanism for the future, however, it can become overprotective such as the case with chronic pain. The good news is that because the encoding process creates a learned response, this response can also be unlearned through neuroplasticity. Neuroplasticity is the term used to describe the constant changes in the brain with learning. Since the brain is constantly creating and revising the connections it makes, the brain can change the neurotags which were imprecisely encoded.

In summary, chronic pain may be a learned response due to inaccurate encoding of the original injury. The encoding of the image in the brain becomes blurry leading to the brain pairing similar movements and situations to the original injury, called stimulus generalization. Since this pairing is a learned response, it also means that the response can be unlearned. Chronic pain can be an incredibly frustrating experience, but know that the brain is always creating and revising its connections.


References

Moseley, G. Lorimer, and Johan W. S. Vlaeyen. “Beyond Nociception: The Imprecision Hypothesis of Chronic Pain.” Pain 156.1 (2015): 35-38.