For a while now I have been attempting to understand Karl Friston's "Free Energy Principle" and it's relationship to pain. I thought I would now try and explain this theory, that has been taking the science world by storm. It is changing how we view not just pain, but also emotion, psychiatric illnesses and many other areas of life. In fact as an unifying theory that is helping us understand life in general.
So this is a BIG theory and as such is very complex, using Bayesian statistical modelling, which I will not go into, as I do not really understand it myself!. However the principles are reasonably easy to get your head around.
As I have stated in a previous blog our brains are encased in darkness, being surrounded by a skull. And yet they give us this incredible world of sights, sounds, smells, touch and tastes. How do they manage this?. Well the theory states that prior knowledge of what previous sensations have meant for us and the actions we have needed to take as a result of those sensations, guide us in our predictions of the meaning of new sensations and our required actions. If you like, our total stored memory of previous sensations allows us to sift through them and best work out what the new sensation we are currently perceiving is most likely to mean and what actions we have taken in the past and how it worked out for us. Basically the brain is not passively taking information about the world from our senses, but is a predictive machine that is continuously active in predicting the world and our required actions in the world. We act upon the world and the world acts upon us.
These predictions, which it must be remembered are occurring in milliseconds and before our conscious awareness of the incoming sensation, travels down through the brain and spinal cord and even into the body, where it meets with the information coming upward towards the brain from our senses, with predictions occurring at multiple levels throughout the system . What happens next is our systems need to work out whether the predictions and the sensory information match. If they do, then that is our experience. If they don't, then this is called an "error signal" and there needs to be either changes in our predictions or changes in our actions to correct the error. The gap between sensation and prediction is "Free Energy" and too much of it leads to "entropy" in our system, or if you like a wearing away. Therefore we need to try to minimise our free energy as too much of it is costly to us as organisms. However we need a certain amount of entropy as changes to our predictions or sensations are learning.A bit like a glass of red is good for you, a bottle a day is not.
Imagine Andy Murray about to receive a serve from Federer. The speed of the service means that his conscious brain does not receive the information quick enough to filter a response. Instead Murray will predict (without his conscious knowledge) from Federer's racket, body position, movement and flight of the ball, where the service is likely to land and having received previous services into that area of a tennis court, he will need to position his own body in the correct way in order to best receive the serve. Along the journey of the ball he may receive information from vision that is novel (the ball is travelling slower or has more spin or hit the outside strings) and this may conflict with his prediction of the Federer serve based on his prior experience of them and errors are created. He might change his body or stick with the prediction. If, say, there has been light rain, or they are playing in high altitude the novel flight of the ball may need to be learnt. The choice for Murray will basically be
1. The incoming vision of the ball matches the prediction- return
2. The incoming vision of the ball does not match the prediction (error signal), changes bodily position/prediction.
3. The incoming vision of the ball does not match the prediction (error signal), goes for the shot anyway.
We tend to trust our predictions more than our senses, which is logical as we have a rich history of sensations and how it turned out, against a novel stimulus. If we called it wrong we can simply update the system (this can now be added to my bank of possibilities of what can happen).
What, I hear you ask, has any of this to do with pain?. As well as receiving information from the outside world we also receive information from our internal world and this is termed "Interoception" or body awareness. It means understanding the signals we are receiving from our bodies, which we also do via the same predictions. A perception of a fast beating heart when we are giving a speech is not actually our heart that we are feeling, rather our prediction of how our heart is likely to feel when we are giving a speech, with the knowledge from our heart that it is beating harder and quicker.
Pain is interoceptive. It helps us know that the body is in danger and to create a protective response (ie move your hand away from the hot plate).However I see many people with low back pain, who did not do anything to indicate they were in danger, often starting when leaning forward to brush teeth or picking something light up off the floor. Similarly with most chronic pain (pain lasting longer than 3 months) whatever caused the pain initially has resolved and pain is now spinning in it's own cycle. Debilitating conditions such as fibromyalgia often have no obvious reason for the onset, and even after a viral illness why is the body still producing pain?.
Going back to Andy Murray, who hurt his hip and has just started his return to tennis at the time of writing this. With regard to his hip pain:
1. The incoming signals (nociception) of danger from the hip (inflammation) match predictions = pain.
2. The incoming signals are saying no danger in the hip and prediction agrees (no error signal)= no pain.
3.The incoming signals from the hip (it is OK) create an error signal as prediction says I am in danger= liklely pain as prediction tends to hold sway.
4. The incoming signals say the hip is not OK, create an error signal as prediction says OK= likely pain if the incoming signals are great, remembering that we are built to see things cautiously. Pain is an important survival mechanism and will generally win out if the signals are divergent.
There are important times when prediction will override the sensory information. When in a war setting and a soldier is shot, they very often experience no pain as prediction states that pain will likely be more unhelpful than helpful. Similarly when a ballerina is dancing on her toes there will be a barrage of nociceptors firing, but the prediction is that it in her overall best interest to keep dancing without pain, therefore no pain will be perceived.Once off the battlefield or stage the prediction will likely be now it is in the individuals best interest to experience pain.
We now know there are many things that can occur to produce a long term magnified sensory input to the brain that is not helpful to us (oversensitive nerves and glial cells and mechanisms that are meant to switch down pain not working correctly, to name a few).This is called (peripheral/central) sensitisation.This can cause sensitivity to light, sounds and clothing on the skin.The mechanism as to why we over predict has yet to be investigated, but it is logical that in the same way a brain can predict a sense of a pounding heart, so too it can predict a sense of pain, even in the absence of nociception.
So what can we do about all this?. Well logic would suggest reducing error signal. Remember that there is very little work carried out to date on treatment approaches using the Free Energy Principle as a model. However there are papers that have looked at using body awareness training for pain and have good outcomes. Also there have been studies looking at using flotation tanks and warm lighting to reduce depression (both working on interoception).
We live in a world full of sensation- telephones, T.V's, monitors and other people. It is easy in this world full of what is called exteroceptive (our senses) stimuli, to not pay attention to our internal world. This may be perhaps one of the reasons why there has been an epidemic of chronic pain. We simply are not understanding or listening to our bodies.
I have been interested in interoception for several years and believe I have a unique approach to management of chronic pain helping to restore a better understanding of our interoceptive networks. As a qualified mindfulness practitioner, the foundations are mindfulness, using techniques such as "body scan", "mindful movement" and "samatha (breath) meditation".These techniques allow time to explore the internal states of the body. As an osteopath I also use pain education- knowledge of why pain occurs reduces predictive errors, resistance band work (muscles are also interoceptive) and visualisations/hypnotherapy (I have a diploma in hypnotherapy).These are built around relaxation and internal awareness.
Interoceptive/body awareness training however has gained interest for the treatment of other recognised body awareness problems such as depression, anxiety, obesity, anorexia, alexithymia and Aspergers.
Have you ever seen people on the street offering free hugs?. Well an interesting fact is that although touch is a ( exteroceptive) sense, if you hug someone longer than 15 seconds it becomes affective touch and has a different pathway in the brain and is part of the interoceptive network. So go hug someone, it will reduce your prediction errors!.
Further reading Suggestions:
Lisa Feldman Barrett- How Emotions Are Made
Karl Friston - Aeon.co- Consciousness Is not A Thing, But A Process Of Inference
Andy Clark-Surfing Uncertainty
Tsakiris- The Interoceptive Mind- To Be Published in Sept 2018 (excited already!).