Episode 22 – Pain (part 1)

The Gorilla experiment
“The Dress” Does it appear gold and white or black and blue to you? Now ask some friends.
For a good overview of the science and neurobiology of pain see this excellent book by Moseley and Butler.

Further examples of visual illusions can be found here. https://www.verywellmind.com/cool-optical-illusions-2795841

Hello, and welcome back. I know it has been sometime since I have produced an episode for this podcast. It has certainly been an interesting year, and I’m sure that many of you, like me, have had their plans somewhat derailed.

It is now over a year since I released a brief episode promising that we would be doing some work on pain, and I think that maybe after such a long break it is time that we got started on the advanced class.

As I mentioned last time pain is a difficult issue both physically and emotionally. It is also extremely complex and poorly understood by both the medical profession and the public. There is an increasing body of evidence that suggests that a better understanding of pain, what it is and how it manifests, can directly and indirectly help in the management of pain. This is not surprising, understanding something helps us find solutions. However, this does not just mean understanding by scientist and professors of pain medicine, in order impact pain it implies a better understanding by all of us, including those who are affected by pain. 

There have been some recent advances in research into chronic pain, and the neurobiological mechanisms that are responsible for pain. However, neuroscience that pushes the limits of human understanding will always stray into the fields of psychology, philosophy and even theology. This is not necessarily a bad thing, and I hope you will see how these disciplines might have a valid role to play, not instead of, but as an adjunct to medical approaches.

I am going to try to explain some of these advances and concepts of pain drawing on all disciplines available to us. As a GP I am a generalist, and I do not pretend to be a neuro-scientist or pain expert. The neurobiology presented here is perhaps a “lay interpretation”, it is how I find it helpful to interpret, understand and explain this work, it is not an academic thesis. If you are interested in the science behind these ideas, as always, I will post some links on my website.

Lets start at the very beginning and ask what is pain?

We often think of pain as a disease, as something that has gone wrong. But this isn’t quite right. Pain itself is a normal part of the functioning of humans. In the first year of medical school they don’t teach you about any diseases at all. Instead they teach anatomy and physiology. They teach you what goes on in the body when it is working well. If we want to understand how something has gone wrong, we first need to understand how it’s supposed to function.

Pain is a warning system. It is there to protect us from harm and keep us healthy and safe. When this system is working correctly pain is a friend, not an enemy. It prevents us from injuring ourselves, we will instantly drop a hot pan because of the pain, preventing burns to our hands. When we are injured it causes us to rest and allows our bodies to heal. If we were unable to feel pain, we would not be very healthy. For example, with leprosy the disease itself does not cause damage to limbs. Leprosy causes loss of sensation, which then in turn results in frequent injuries, like burns or cuts as people lose their natural waring system.

Because the primary function of pain is to warn us of danger, and to protect us from harm, the mechanisms that produce pain are more complex than simple cause and effect pathways resulting from injury in the body tissues. Our brains use pain to alter our behaviour based on what it calculates will insure our survival. This is not only dependent on the type of injury, but also on context.

The intensity of pain we experience is therefore not just related to the severity of the injury itself but also on the situation. For example, if you were to twist your ankle chasing a deer you are likely to feel pain in the ankle. The brain wants you to rest and avoid doing more injury. But if you were to twist your ankle running away from a lion it is unlikely you will feel any immediate pain. Your survival depends on you being able to carry on running and so the brain will judge that it is not in your best interest to make you feel pain.

When you twist your ankle the injury triggers pain receptors in the tissue, which in turn send a pain signal up sensory nerves in the spinal cord into the brain. But this signal is not “the pain” itself. The brain must interpret the stimulus to decide how dangerous it thinks it is, and the brain then “generates” the amount of pain it thinks is appropriate for the perceived level of danger or situation. This will consider many external factors not necessarily directly related to the initial signal. More than this, if the brain believes you are in danger it may make you feel pain even in the absence of any injury to the tissues at all. A great demonstration of this was a case report that appeared in the British Medical Journal in 1995. A 29 year old builder presented to A+E after having jumped down onto a 15cm nail which had impaled right through the boot. He was in such agony that he had to be sedated with fentanyl and midazolam – the most powerful drugs available in the emergency department, before the nail could be removed. However, on removing the boot it was found that the nail had passed right between his toes, with no injury to the tissues at all. It is important to understand that he was not imagining the pain. He was not making the pain up. He genuinely felt the pain. The brain was giving him maximum pain as it judged it was extremely important to his survival that he shouldn’t walk around with a nail through his foot. Given that on the balance of probability the nail was most likely going through his foot this seems a sensible approach, at least until more information was available. The purpose of this system is to protect us and keep us safe. When it is functioning as it should pain is always our friend.

Of course, I understand that for many of us pain is certainly not a friend. As we discussed the first time we approached this subject on this podcast, chronic pain is one of the hardest and most debilitating conditions I treat. But if pain starts to harm us instead of helping us, for me this must mean that the pain system itself has malfunctioned. If the brain is giving us pain in situations where our survival and wellbeing would be better served without the pain, then the pain system has gone wrong in some way. I like to compare this to autoimmune diseases, such as RA and IBD. The immune system is designed to protect us and keep us safe, killing off invading bugs. But sometimes it develops a fault and starts attacking healthy tissues and causes us harm. When we start to experience pain that is making our lives worse rather than better, because of excessive intensity of pain, or pain that continues for months or years, this means that there is a problem with the pain warning system. It is designed to help us and not harm us, and if it is harming us it has malfunctioned in some way.

Now this is where things can get a bit tricky. This concept of a malfunctioning warning systems is often misinterpreted. People sometimes understand this as meaning that the pain is “in the head”; that this “brain pain” is somehow not real, or less legitimate, than “body pain” produced by a correctly functioning pain system in response to injury to the body. This represents a fundamental misunderstanding of the interaction between the world, the human brain, and human experiences. It is where neuroscience meets the philosophy of mind. These are complex topics, but extremely important ones. Strictly speaking the pain is in the head in that it is produced by the brain, but this is true of all pain, and in fact of all human experience. “Brain pain” is not a fundamentally different type of thing from other forms of pain. This is hard to untangle, but I will try to explain. We may need to go slightly off-piste, but I think it is necessary, so bear with me. 

We know that all types of pain are generated by the brain. All pain is “in the head” because pain is an experience, and experiences are mentally generated. In the same way, all our senses are generated by the brain and are therefore “in the head”. What we see, hear or smell are projections created by the brain in response to the external stimuli it receives.  The way we “see” the world around us it is not like looking at it through a window, it is more akin to seeing a representation generated by a computer and displayed on a screen. What we see is dependent on the way the brain processes information, and what it decides to present to us. Because of this the experience of the colour or smell of an object is not the same as the object itself. We can never know if someone else’s “experience” of the colour blue, for example, is the same as ours. We have no access to the experience their brain conjures when they look at a blue object. The experience they call blue may in fact be the same experience we call orange. Back in 2015 there was a viral sensation on the internet of a photo of a dress which people either saw as black and blue, or white and gold, people argued over which it was and formed into strong camps which some referred to as #Dressgate. The point is that the particular combinations of light waves in the photo caused different people’s brains to produce a different experience. Neither is right or wrong, both experiences are equally legitimate and equally “real” to the person experiencing them.

Because of this system all of our sensations are dependent on context in the same way that pain is. The brain generates experiences of sight, smell, sound and touch based on what it calculates will be beneficial to show you. There are lots of examples of visual illusions such as the spinning dancer or the rabbit:duck image, which demonstrate that what we see depends upon the way our brains interpret data to build a picture or representation of the world. It’s worth checking out some of these when thinking about this work, even if you have seen them before its worth checking them out again. It’s like cornflakes, you kind of forget how good they are. I will post some links to these and the dress image, and recommend you check them out, it’s helpful to see this in action. To me the dress looks white and gold, whilst to my partner it is black and blue.

Context plays a role in all our perceptions. We will often see what we expect to see. The brain is constantly taking short cuts, and generating information based on what it predicts will happen. Because it receives such a huge quantity of data the brain will process this and decide what it thinks it is most important to present to our awareness, if it didn’t we would be overwhelmed by information and wouldn’t be able to get anything done. This may involve not registering certain events that it deems to be irrelevant to the situation, or filling in the gaps when information is incomplete. A good example of this is text where all the letters in the middle of each word have been scrambled, with only the first and last in the right order. We can easily read this text and may not even notice the scrambled words. When we expect to see something our brain may present us information even if it is not really there, and when we do not expect something we may fail to see it even if it is right in front of us. Think of the favourite example of the gorilla experiment. It’s so well-known I won’t go into it here, but if you have never seen it before go check it out on youtube, again, I will add all the links to my website.

In 2001 at the university of Bordauex an experiment was conducted where wine experts were asked to comment on two wines, one red and the other white. In fact, they were comparing the same wine, the “red wine” was actually just the white wine dyed red and served at room temperature. All 54 experts were fooled by the experiment and described the wine as you would expect for a red, “rich cherry notes and subtle tannins”. It wasn’t that they were making it up, or that they were charlatans, they actually experienced a different taste, the brain created a different experience based on its expectation. And it did it universally, all 54 were convinced.

This is not just true of visual illusions or psychological experiments. There are lots of examples of the importance of context to our experience in everyday life. For example, have you ever been working and taken a swig of tea or coffee that has gone cold. It’s disgusting and makes you gag. But is cold coffee really disgusting? I absolutely love iced coffee on a hot summer’ day. It tastes disgusting because the brain was expecting it to be hot, it was surprised by it being cold. This surprise, the unknown, is interpreted as danger. Going around drinking unidentified liquids is not normally a good survival strategy, and so the brain made it taste disgusting, so you spat it out. Maybe it also calculated that it didn’t want to destroy your laptop so you managed to spit it back into the cup, maybe not.

This is the nature of all human experience, and is the reason why philosophically speaking it is impossible to prove that anything exists outside of your own experience, and why trees falling over in forests with no one around to hear them don’t make any sound. If you think this sounds doubtful check out John Locke and his theory of primary and secondary qualities. These ideas can be traced back 2.5 thousand years, to Plato and his allegory of the cave. A modern twist on the same idea is the film “The Matrix”. If this stuff interests you, for a good introduction and overview of some of these philosophical concepts I would recommend the podcast “Philosophise This!”

So we know that in one sense none of our experiences are “real” in that they are all generated by our brain, as a projection of useful information about the world around us it decides to present to us. We can never see of feel an actual material table; we only experience the image or feel of a table presented to us by our brains. On the flip side, all our experiences are “real” in that we experience them. If we see a table, we have experienced the image of a table, we can never be said to have not seen it. The experience of seeing the table was a real experience.

Likewise, pain is an experience, and there is no such thing as pain outside of this experience. Pain does not exist “in the world” it only exists as our personal experience of it. In this sense all pain is “in the head”. It also means that there is no such thing as “imaginary pain”. It is impossible to experience pain that is not real. If we have pain, we have pain. If we try to imagine being in pain this is not the same as feeling pain, although if we imagine it for long enough and hard enough we might, because the brain is a powerful thing, but if this happens we would no longer be imaging it, we would be experiencing it for real and we would genuinely be in pain.

If you cut your finger with a knife the pain is not in the knife, and it’s not in the cut, or in the finger, it is generated in the brain as a response to a message sent from nerve fibres in the finger, and the brains interpretation of the meaning of this message, and the surrounding context. The pain itself is produced by the brain, it is a mind experience. This means that it is possible to experience “real pain” in a part of the body even if there is no injury or insult to that part of the body. Just like my cold coffee tasted like poison even though it was perfectly safe. There are lots of examples of the brain producing pain without a physical stimulus in the tissue of the body. The classic example is that of a phantom limb, where people can experience pain in a toe even after their leg has been amputated. Scientists have conducted fascinating pain experiments where people are made to feel pain in artificial limbs, and even in other people’s limbs!

At risk of labouring the point I want to clarify this with an analogy. I apologise if you are already with me and I’m over egging the pudding, but I think this can be a slightly tricky concept. Think of the human experience (a colour, or smell, or a pain) as the experience of listening to Mozart’s Clarinet concerto. In order to hear concerto, in order for it to exist, Mozart first has to write it. For our analogy, in terms of a colour, this might be the existence of a blue object in the world, for pain it might equate to damage to the tissues, let’s say a pin pricking a finger. However, Mozart thinking up the piece is not the same as the music itself, it’s just in his head and nobody else can hear it. He must first write it down. So, he writes the score. The score might be analogous to light bouncing off the blue object and landing in the eye. In the dark a blue object is not blue. In terms of pain it might be the activation of pain nerves sending signals into the brain. But even this score is not the same thing as the music. Although it may be said to in some way contain the music, or has the potential to become the music, it is not itself the music. For the music to exist you not only need the score, but you also need a bunch of musicians with a bunch of instruments to play it. In our analogy these are neural networks, and the orchestra is the brain. The musicians must interpret or decipher the score to produce the music. In one sense ultimately the music is not created by Mozart, or by the score, it is produced by the musicians. Without the musicians the music does not exist at all. Now, although the music could not have existed without Mozart, because he wrote it down, it can continue to be played long after he has died. And the experience of it will be different depending on the way the score is processed and represented. If it is played on a trombone it will sound quite different than if someone plays it on a flute. Neither is wrong, or a misrepresentation, its simply different ways of processing the signal to produce a different experience. Moreover, if all the musicians have learnt the piece off by heart, they may be able to play the piece even if all the copies of score were lost in a fire. The experience of hearing the symphony is no less real, no less intense, or legitimate, regardless of whether Mozart himself is conducting or the musicians have copies of the score.

I think that is enough for this episode. This stuff can be confusing and hard to follow. Let’s take a break, but your homework this week is to go check out the various visual illusions and experiments, and think about how your perception of the world is a construct of your brain. Next time we will move forward and think about what this means when it comes to understanding chronic pain, and how understanding these concepts can help us to find new ways of addressing and treating pain.