The basic idea is that chronic pain is often driven by dysregulation of a “supersystem” that coordinates defensive responses to injury.
The supersystem results from dynamic interaction between different subsystems, most notably:
- the nervous system,
- immune system, and
- endocrine system.
Following is a detailed but simple description of what we can learn about chronic pain from this systems perspective. And more importantly, what we can do about it.
First, a bit of warning. This article is a little bit on the long side. But it’s one of the best articles I’ve written.
Complex adaptive systems defined
A complex system is composed of parts that interact to produce collective behaviors that are more complex than the sum of the individual behaviors
A complex adaptive system, such as an organism, is one whose behavior is not merely reactive to its environment, but purposeful and proactive. Thus, a complex adaptive system has some degree of agency and intelligence.
Emergence and lack of central control
In a complex system, control is not located in any particular area, but emerges from the complex interactions of all the different parts.
Complex adaptive systems are nested – they are composed of subsystems, which are in turn composed of smaller subsystems, which have their own subsystems, etc. For example, the nervous system is made of parts like the brain, spinal cord and peripheral nerves, which are made of different types of cells, and so on.
Each subsystem has varying degrees of agency and intelligence. For example, a neuron can in some sense “decide” which neighbors to form synapses wit
We can turn our attention to various levels of heirarchy in the nested systems, zooming in and out of focus on different levels of complexity.
For example, in examining why someone has pain, we can focus attention on the nociceptors. Although they are a relatively stupid and robotic little subsystem in the pain alarm supersystem, they do have some degree of intelligence, and can “decide” whether to report certain threats to the brain. We can alter their decision-making behavior, for example, by taking NSAIDS to reduce local inflammation and lower their sensitivity
The dorsal horn of the spine is a more complex subsystem with more moving parts, and therefore more intelligence and agency. It receives nociceptive signals from the periphery and then decides whether to report them to the brain. Like the peripheral nerves, the sensitivity of the dorsal horn can be adjusted
As we look at higher level supersystems like the brain, we find far greater levels of intelligence and control over pain. Because this intelligence does not live in any particular place, but instead in a fabulously complex web of connections, creating change does not involve flicking any simple switches.
Homeostasis, stress and hormesis
Complex adaptive systems change so they can maintain a state of balance in relation to a changing environment.
Homeostasis is a state of balance providing the minimum or essential conditions for life. If the body does not preserve homeostasis by remaining within certain ranges of heat, fluid levels, blood pressure, it will die.
Allostasis refers to a slightly different concept – it is the dynamic process of changing states to adapt to the environment. Thus, an optimal state of balance is not static, but always shifting dynamically.
Stress is the process of using resources to respond to external or internal factors that push the system out of balance. For example, injury is a stressor that create a stress response. The stress response usually has three stages – alarm, resistance and recovery.
Hormesis occurs when a small amount of a certain stressor is beneficial, while larger amounts cause significant harm.
Exercise is the best known form of hormesis. The right dose – not too much not too little – helps tune and regulate the stress response system, making us healthier, and better able to withstand the same stressor in the future. What is less well appreciated is that the same rule applies to almost any kind of stressor,
States and phase shifts
Complexity theorists use the term “state” to refer to all the different ways that a complex system can change in response to stressors or other inputs from the environment. These changes are often nonlinear, which means that small perturbations to the system can produce large changes, or that large perturbations might produce very small changes
A significant non-linear change is called a phase shift
Certain chronic pain states such as allodynia (pain without tissue damage) can be understood as a phase shift in the behavior of the supersystem that governs response to injury.
How do complex systems without any central control maintain homeostasis and create adaptive responses to stress? Why does this control just “emerge”?
Part of the answer involves the concept of attractors. Although complex systems can potentially arrange themselves into an almost infinite number of different states, there are certain states they tend to move toward. These states are called attractors, and they contribute to stability.
A severe injury might perturb the pain alarm system to such a degree that baseline pain sensitivity levels don’t return to normal, even after the injury has healed. Chronic regional pain syndrome (CRPS) is an example of phase shifts causing severe dysregulation of the defense supersystem.
Negative feedback means that when the system detects a change in a particular direction, this will encourage a change in the opposite direction.
In a positive feedback loop, a change in one direction creates feedback that encourages a similar change. This basically creates a vicious circle.
A positive feedback loop can create change in the body very quickly, which is necessary to deal with an emergency. Because positive feedback loops move the system away from equilibrium, they are usually under the control of an overarching negative feedback system that prevents loss of balance.
Interestingly, many people suffering from chronic pain, including TMJ, IBS, and fibromyalgia, are known to have problems activating descending inhibition. From a systems perspective, this means that their negative feedback loops are not kicking in to control positive feedback loops.
Positive feedback loops probably play a major role in allodynia, migraine headache, and a variety of autoimmune disorders. In each case, a stimulus causes the system to get out of control very quickly.
The relationships between all the different parts of a complex adaptive system are more important than the parts themselves. For example, the incredible intelligence and complexity of the human brain is owing to its connectivity
In the context of a stressful event such as an injury, the connectivity of the major subsystems – nervous, immune and endocrine – ensures that a response is systematic, global, and highly coordinated. This connectivity creates an hugely complex array of negative and positive feedback loops that organize a response.
If you would like to read a lot of heavy detail on the exact nature of the interactions between these different major subsystems, check out the paper here.
This paper identifies four types of dysregulation that might cause chronic pain.
Many people have huge room for improvement in the way they eat, sleep, exercise or handle stress. They might be more motivated to make those improvements if they better understood the connectivity of all the different systems in the body, and their potential relationship to chronic pain.
Local problems can also be complex
From a systems perspective, we can look at these conditions as involving a phase shift in the quality of the tissue, brought on by stressors that arrived with enough frequency and/or intensity to overwhelm the adaptive capacity of the local repair systems
Some people are sensitive
The supersystem that coordinates defensive responses to threat can be set to higher or lower levels of sensitivity.
For the sensitive person, whenever there is a threatening stimulus – injury, work stress, illness, lost sleep, eating the wrong food – there is a strong defensive response. The person may feel tired, weak, sore, or otherwise very out of sorts after being exposed to even minor stressors. Many of these people have suffered some form of serious trauma in their lives
On the other hand, some people have a defensive system that remains very stable even in the face of significant threat. These are the people who can run a marathon, get in a car accident, work 80 hours a week, give birth to twins, and still go about their lives with no dip in energy, vitality and well-being. As if nothing happened at all!
Another useful idea is that sensitivity levels can change
Progress is non-linear
Because complex systems often change in a non-linear fashion, we can expect progress to be non-linear as well.
That means getting better is often a question of moving two steps forward and one step back. In the short term, this makes it difficult to discern positive change. But over a larger timeframe, a pattern of progress may become clear.
Humans evolved in a social context, and therefore some of our defense mechanisms, including pain, are designed to motivate behaviors that seek help from others.
Our health care system is amazingly good at dealing with acute injuries. It has a long way to go in treating the global, systemic and complex problems that are currently the biggest health problems we face – obesity, diabetes, chronic pain, etc.
We can understand the essence of these problems better with the systems perspective, and hopefully this will allow us to see that these problems will not be solved by highly specific interventions