Pain is one of the most common reasons why we contact medical and health centers. In hope of answers to why we feel the way we do and in hope of a cure, pain relief, advice and reduced suffering, we seek help from doctors, therapists and various specialists.
In general, pain is believed to be a direct response to damage or irritation in the body's tissues, probably largely due to the fact that the French philosopher René Descartes coined a "church bell theory" for pain in the 17th century - when you pull the rope to a church bell the bell strikes. Descartes believed that damage to the body's tissues leads to pain, via directly connected nerves from tissues to the brain. He was somewhat on the trail but at the same time very far from the whole picture.
Descarte's deficient theory underlies Western pain treatment and diagnosis and still influences how we view pain - a sensation that arises as a result of tissue damage, and nerves that convey this message to the brain. This would mean that the intensity of pain we feel should be in direct proportion to how irritated our body tissues are, and that different people with the same diagnosis and degree of injury / irritation should experience pain to the same extent. After many years of experience in pain physiotherapy and rehabilitation, it is not difficult to reject such a conclusion. The question remains, however - what is actually going on?
Pain - An experience
IASP (International Association for the Study of Pain) defines pain as follows. ”Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. A key word in the IASP's definition of pain is "experience". Regardless of experience, an experience is always personal and everyone who deals with pain knows that pain is a personal experience.
I wrote earlier that Descartes was somewhat on track with his theory of pain, but that his theory at the same time is very far from the whole picture. How we experience pain may definitely be affected by our tissues, but our pain experiences are also affected by other sensory input and by a vast number of other factors in our lives. Emotional states, thought processes, experiences, memories, prejudices, expectations, attitudes, culture, society, stressors etc. also plays a major role in how our nervous systems work, and thus also in how we perceive and experience our bodies.
Acute pain
In healthcare, it is common to distinguish between "acute pain" and "chronic pain". Pain that has lasted longer than three months is usually referred to as "chronic pain". "Chronic pain" gives me a feeling that the condition is static and unchangeable and therefore I myself prefer to use the term "persistent pain". Pain that has lasted less than three months is often referred to as "acute" or "subacute".
Acute pain is something we experience for a while, usually post-injury or after some type of overexertion. If we e.g. injure our foot, we experience pain as a consequence of warning signals reaching our brain from nerves in e.g.muscles, tendons, bones, ligaments or skin in the foot. The brain decides there might be danger and that the warning signals should be prioritized and thus creates painful physical experiences. The pain we experience is part of our "built-in" alarm system, which signals that we are under attack and that we should take care of the injured area for it to be able to heal properly and for us not to aggravate the injury.
A vast number of different physiological and immunological processes in affected tissues and cells follows an injury, in order to let healing start taking place. These processes also include influencing how we as individuals think, feel and use our bodies - all to optimize the healing process. Our nervous systems usually adapt to healing, which leads to a gradually decreasing flow of warning signals to the brain and thus our experience of pain also tends to decrease over time. Acute pain can also occur in absence of tissue injury.
Persistent / Chronic pain
Persistent pain starts as acute pain but persists over a longer period of time. Sometimes persistent pain develops post-injury but remains for various reasons even though the injury has healed. Persistent pain may also develop without underlying tissue damage or irritation. It is not uncommon for various examinations to show no clear underlying cause for persistent pain, or for our experience of pain not to be in direct proportion to what examinations can show.
Research has shown that our nervous systems respond to the experience of pain by increasing their capacity to process warning signals, pain is prioritized, so to speak. This means that our central nervous system (spinal cord and brain) begins to respond differently to warning signals sent from nerves in the body's tissues. Practically this means that our experience of the body changes and no longer provides an accurate reflection of what is going on in the body's tissues.
Imagine for examplethat you are listening to live radio and someone is turning up the volume amplifier. When the volume amplifier is turned up, you percieve the sounds as louder, even though those who speak or sing in the studio do not change their voices. Another example, could be a sensor lamp. If the sensor is set too sensitively, the light turns on already when someone is moving on the neighbor's driveway. In these metaphors, the volume amplifier and the sensor represent parts of the central nervous system. When we are burdened by persistent pain, the radio's volume amplifier is often turned up or the lamp's sensor becomes more sensitive. An engineer might say that we have an electrical fault rather than a mechanical fault. In medical terms, we are now talking about central pain sensitization.
Pain - A potential threat in our awareness
Thanks to modern research, we can today examine the brain and its activity at the very moment when someone experiences pain, and in short, we can say that the experience of pain is very complicated. René Descartes was right that pain is an experience created by the brain, but today we know that pain and the pain system are much more sophisticated than just a direct answer to how the body's tissues feel and function.
The brain registers more or less everything that happens within us and in our environment but sifts out among all the information and only a small fraction of all information reach our awareness. The experience of pain and other unpleasant bodily sensations is information that our brain tends to prioritize, as pain is seen as a potential threat.
Since pain and other threats or warning signals are prioritized and attract our aware attention, there is not as much room for other sensations, impressions and experiences and thus our attention overlooks these. If we e.g. encounter a bear, it is not easy to notice and process anything else within us or in our environment due to the fact that the majority of our nervous system is mobilized to deal with survival and the threatful situation.
Brain research also shows that emotional states, thought processes and how we cope with them affect our nervous and pain system, and these get integrated into the actual experience of pain. It is often said that "age doesn't come alone", the same can be said about pain. With very few exceptions, pain is never an isolated event in our awareness, but is always accompanied by thought, feeling and meaning.
Pain - Nerve cells communicate
Nerve cells in our nervous system "communicate" with each other through "signal substances" - one nerve releases different signal substances that the next receives through "gates". Communication between two nerves is called a "synapse". Depending on the type of substance that is released and to what extent, the receiving nerve responds by opening or closing its "gates". Open gates allow one nerve signal to pass from one nerve to the next. In order for us to experience bodily sensations, such as pain, in response to something happening in the body's tissues, "gates" needs to open in certain parts of our nervous system.
When a central pain sensitization develops, which is often one of the reasons to why we experience our body as we do when we are burdened by persistent pain, the nervous system tends to adapt to the increased sensitivity by increasing the number of gates in nerves in the "pain system", in the spinal cord and in the brain, which receive signal substances and some gates begin to be kept open longer than normal. This leads to an increased flow of warning signals to the brain. If the flow of warning signals increases, so does the threat picture in the brain and as I mentioned earlier, our brain prioritizes potential threats. In the previously mentioned metaphors, this means that the sound amplifier on the radio is turned up or that the sensor has been set too sensitively on the sensor lamp. The conclusion of this is that our brain receives more and stronger warning signals from the spinal cord, which distorts the brain's perception of the bodily tissues' state. The information the brain receives no longer provides a correct reflection of the tissues, which usually means that our experience of pain changes and the threshold for us to experience pain becomes lower.
How these gates open and close, and what the result of that may be, is a complex process that modern pain research invests resources in. We know that tissue damage and various types of inflammatory conditions and injuries affect how gates in parts of the nervous system open and close, and this in itself can in the long run lead to the “volume amplifier of the pain system” being turned up. Today, however, we know that an vast number of other factors also affect how the nervous system "communicates", and thus contribute to influencing the "volume amplifier or sensor lamp in the pain system", ie the sensitivity of our nervous systems. Attention, thought processes, emotional states, internal and external stressors, immunological and hormonal processes, information from all our sensory organs and a constant interaction between these factors majorly affect the way nerve cells in the body, spinal cord and brain communicate with and signal each other.
Pain - The brain learns
Networks of thousands of nerve cells in different areas of our brain are in one way or another behind every specific experience we have, including the experience of pain. Likewise, thousands of nerve cells in the brain communicate, extremely well-coordinated, when the brain gives the body some kind of command , e.g. as we move our bodies in any way.
Let's take a musician playing in an orchestra as an example, a cellist. To create sweet music together with the orchestra, the cellist needs to handle the bow with one hand and the strings of the cello with the other with incredible motor precision, while following the conductor and the rest of the orchestra attentively, alertly and relaxed. For this to be possible, the cellist needs to have exercised his/her motor and musical skills, his/her attention and sensitivity persistently for many years. During all years of training, the brain has developed and strengthened networks of millions of nerve cells to be able to give the body's muscles precise commands and at the same time process other information. Practice makes perfect.
Sensory experiences, such as the experience of pain, are also created by networking nerve cells in our brain. Just as motor networks in our brain are developed, strengthened and fine-tuned by exercise, sensory networks can also be "exercised". That which the brain exercises and what we pay attention to, the brain gets better at. With persistent pain, millions of nerve cells in different areas of our brain have for a long time created networks that are constantly adjusted and changed. Over time, it becomes easier for the brain to activate these "rehearsed" networks of nerve cells in a well-coordinated manner. The experience of pain is thus triggered more easily.
Pain - The brain creates associations
A well-known example of associative learning is "Pavlov's dogs", where Ivan Pavlov researched salivation in dogs. When Pavlov gave food to his dogs, the dogs salivated. Before the dogs got their food, Pavlov rang a bell and the dogs quickly learned to connect the sound of the bell with getting food. Pavlov noted that the dogs eventually began to salivate only by ringing the bell, before they were given food. When we learn to connect one thing with another in this way, it is called classical conditioning or associative learning.
As with other types of experiences, associative learning or conditioning can also develop in pain experiences. It is more common that such mechanisms develop in persistent pain states. The brain then gets more time and more opportunities to create, repeat and strengthen connections and networks of nerve cells between experiences of pain and other experiences, contexts, situations, body movements and -positions, thought processes, emotional states, etc.
It is not easy to understand our human experiences, not even those that at first glance may seem relatively ordinary. Pain as unpleasant experiences we all for natural reasons would rather be free from and fortunately pain research in recent decades has been able to provide us with lots of new discoveries and insights, which may offer support and/or relief to people living with pain. Modern pain research also helps us who work with pain management to offer help and support in different ways to people who for one reason or another live with pain. In pain science there is though still a vast empty space we do not really understand, but the research continues and develops all the time and will most probably continue to shed light on things that yet is hidden in the dark.
To summarize a long blog text, experiences of pain, especially with persistent pain, are much more complex and sophisticated than direct answers to what is going on in the body's tissues and in what condition the tissues are. It feels appropriate to conclude this blog text by repeating the IASP's definition of pain. "Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.".....AND.....Pain is a personal experience and regardless of the underlying causes and for how long it has been part of our awareness it is a real experience that is manifested in our consciousness.
// Jonas Lönnqvist, Body-Mind yada yada