Why Your Pain Hurts: From a Bayesian Brain Approach

If you have been following our blog for a while, you would know we highly, highly emphasise that pain does not equal to damage. This is confusing to most people because we think of our symptoms in the biomedical model. What if we are all wrong?

The biomedical model sucks.

For most parts of musculoskeletal care, the biomedical model does not explain how our pain behaves. The biomedical premise suggests the brain receives a certain stimulus from the body and converts these signals into our conscious experience – our symptoms as we know of them. This is not true. We know it is possible to experience a lot of pain without any injury. This case was published in the British Medical Journal (1995):

“A builder aged 29 came to the accident and emergency department having jumped down on to a 15 cm nail. As the smallest movement of the nail was painful he was sedated with fentanyl and midazolam. The nail was then pulled out from below. When his boot was removed a miraculous cure appeared to have taken place. Despite entering proximal to the steel toecap the nail had penetrated between the toes: the foot was entirely uninjured.”

The reverse is also true – you can experience close-to-nothing symptoms for a traumatic injury. An article in USA Today reported that there was a construction worker who had unknowingly shot himself in the head with a nail gun (as imaged above). Having no idea of his injury, he attributed his symptoms to a toothache and made a trip to the dentist six days later! It was the dentist who discovered the nail. Imagine that!

So what is going on here?

Our brain also sucks

We know placebo works. We know sham modalities of every kind – from spinal manipulation to surgery – produce some positive effect despite having not changed anything from a pathophysiological perspective.

Our brain is constantly dealing with a continuous influx of overwhelming signals coming from our body. It is theorised that to make sense of these signals, your perception of the world is more of your brain guessing what is happening than what is actually happening in the world as is.

In the context of pain, we feel pain because our brain predicts that we are in pain based on the incoming sensory stimulus, our prior experiences, as well as the the contextual cues.

Mind blowing aye?

How does this help my recovery or pain experience?

If you understand pain using the same framework, relief (or resolution) of symptoms does not occur on the premise of restoring bodily function to “pre-injury” state. Your relief occurs when the brain interprets changes in your experience of certain stimulus as improvement. The assumption that we must restore our body to a healthy bodily state in order to find symptom resolution is honestly – by current research and understanding of pain – archaic.

Research tells us you can fight pain by changing contextual factors. Studies have shown that supportive verbal cues from a trusted clinician are central in eliciting placebo effects and inert therapies when presented to patients as an expensive drug performed almost as well to the actual drug itself. Observing first-hand how a treatment have an effect on others also greatly contributes to an individual’s placebo responses.

What? Why have I never been told about this?

Well, now you know.

A paper published in 2006 (that is 13 years ago!) compared surgeons to shamans. The author compares the pre-surgery routine of a modern operation to resemble ritualistic practices utilised by shamans (traditional healers).

Reference:

• Dimsdale J, Dantzer R. A Biological Substrate for Somatoform Disorders: Importance of Pathophysiology. Psychosom Med. 2007 Dec; 69(9): 850–854.
• Fisher JP, Hassan DT, O’Connor N, BMJ 1995; 310:70. (Unusually this case image is untitled).

Additional information:

This entry is largely based on a paper from the prestigious journal Pain titled Symptom perception, placebo effects, and the Bayesian brain published January 2019. So, I love the co-author Ted Kaptchuk – mostly because he did his undergraduate training in East Asian studies and fifty years later? He is a full Professor of Medicine at Harvard Medical School. Amazing right?

What is the Bayesian brain?

To understand the Bayesian brain, you’d have to first understand Bayes’ Theorem. Long story short: every test makes mistakes but if you know the probability of the errors occurring, you can account for them to give you the correct outcome. I wish I could explain it better but it is not really my speciality. It is best you try the link above.