Chronic pain: Can we find a solution inside the brain?
20 percent of Danes suffer from chronic pain, and it is a massive burden on health systems. Here is what we know about how pain is perceived by our body and how new neuroscience insights can help us control it.
The vast majority of people experience pain in daily life. And this a good thing as this protects our body.
Despite being unpleasant, pain has an extremely important function for our bodies. Pain is part of an alarm system that goes off every time our body is either in danger of getting hurt or has just got hurt.
Pain signals allow us to pay attention to something wrong that is happening to our body, so that we can act.
The problem is when pain becomes chronic.
When pain has been present most of the days for more than three months we define it as chronic. Chronic pain is the most common disease worldwide affecting 20 percent of the general population. It is hard to treat, and it has huge economic costs to health systems in Denmark and abroad.
Moreover, pain may change the way we process information and the way we behave. We believe that exploring how our brain is influenced by chronic pain is the key to better control chronic pain in a more effective and targeted manner.
At the Center for Neuroplasticity and Pain (CNAP), Aalborg University we focus on non-pharmacological ways to restore normal brain activity associated with pain. In this way we are trying to improve our knowledge about pain mechanisms in order to decrease the personal and societal burden of pain.
The bodily chain reaction to pain
Pain signals are generated when our body is threatened with injury. When in pain, several of our body systems will be activated.
Our heart will beat faster and stronger and some hormones such as cortisol will be released, which helps us to be alert and to modulate inflammation.
Our body will activate the immune system and the coagulation system, and the healing process will start, with the production of more defense cells and proteins.
Our appetite will change, and our metabolic needs will also be modified.
The sensory information coming from the lesioned area will be magnified and intensified, so that it will become clearer where and when it hurts.
Our memory system will also be activated so that we can have access to our past experiences.
The personal and cultural memory when handling pain
Our brain always contextualizes our current pain in relationship to our previous experiences and beliefs.
This will influence how we will manage our pain. If we had bad experiences with pain in the past, our memories may lead us to take extra care with the injury.
On the other hand, successful past experiences managing pain will weigh positively in its management.
Contextual and social cues on how pain is managed in our family, friends, and in our general culture may influence how we perceive, interpret and report pain.
Additionally, when we are in pain, we tend to protect the painful body area. This is probably to allow our injured body part to heal and not be injured again, making it more likely to recover fully.
How do we control pain?
Not only can our brain perceive pain signals coming from the body. It is also able to actively modulate it, increasing or decreasing the actual perceived intensity of the pain according to context - in other words: how much it hurts.
Just think of a football player who, during the match, is able to keep playing and score a winning goal despite an ankle torsion.
Our brain and the spinal cord have a series of coordinated systems that act like fire fighters, decreasing and controlling incoming painful stimulus all the time.
This is called 'descending pain' modulatory systems. They are designed to handle acute pain and is a part of our body's protection mechanism.
These systems may be more or less efficacious across different individuals based on their genetic background. It is, however, also modifiable by factors related to daily life such as bad quality of sleep, poor physical conditioning, depressive symptoms, anxiety.
Additionally, experiencing pain for a long duration of time can “wear out” and temporarily weaken this system.
What if you can't feel pain at all?
Some diseases may affect our ability to perceive pain, such as diabetes and some rare genetic or infectious disorders. If pain signals are not transmitted to the rest of the body, individuals’ risk to undergo lesion without perceiving it.
It means that a person may have a foot lesion that goes unnoticed, so that it expands and becomes more severe, until it is finally discovered because of bleeding, bad smell or because it becomes infected.
Even worse, death may occur due to appendicitis or heart attack, since pain is main alarm signal for these diseases, lack of pain sensation may delay patients from getting timely care.
Patients who do not perceive acute pain must learn to actively examine their bodies and to routinely check for new lesions, so that injuries can be detected at an early stage.
But what about those instances when pain is chronic?
As mentioned, pain is considered chronic, when it lasts more than the time necessary for tissue healing (most days for three months).
Not all chronic pain is the same, though.
Some chronic pains are related to specific diseases. They are called »secondary pains«. Secondary pains include chronic pain after surgery, pain related to cancer or diseases affecting the brain such as Parkinson, disease just to name a few.
Other pains are called »primary pains«.
The most common disease in the world
Primary pains are not caused by another disease, instead, they are the disease themselves.
Primary pains include migraine and most of the chronic headaches and most of the lower-back pains. In fact, these primary pains are the most common diseases all around the world, affecting more people than depression, diabetes, hypertension, or cancer (see here and here).
In chronic pain, an unexpected fact occurs: we can no longer find a correlation between the intensity of tissue lesion and the intensity of pain.
It is not uncommon to have an instance when a lesion to a part of the body was already healed, but a person continues to experience pain coming from that body area.
In extreme cases, pain may be felt in a body part that is no longer there, such as pain that occurs in a limb after it was amputated.
This is called phantom-limb pain and is related to the fact that the brain representation of the amputated limb is still present after the limb is disconnected from the body.
However, the brain that is deprived of sensory inputs from a region of the body will process information in a distorted and altered manner, which may lead to pain or process pain information from the remaining body part differently.
How can this be possible?
All pains are perceived by the brain, which receives information coming from nerves that innervate the different body parts.
In some persons, the continuous use of the pain pathways connecting an injured body site via peripheral nerves to the brain may cause long term changes in both the brain and the peripheral nerves (the nerves that connects the brain and the spinal cord with rest of the body).
These structures may »learn« how to process pain signals better and more intensely. The nerves and the brain may become so efficacious at processing pain that pain may continue to be processed even after the original lesion is gone.
Exaggerates pain signals to the brain
Peripheral nerves specialized in pain transmission may also become injured themselves and may produce exaggerated and spontaneous electrical activity at injury sites. In this way the brain will receive an exaggerated amount of pain signals.
Take for example a chronically painful shoulder:
Here the remaining normally functioning pain nerves will transmit painful signals coming from the shoulder joint and muscles to the brain. Injured nerves from the shoulder, which were also included in the lesion will generate themselves abnormal pain signal, which will also reach the brain.
The brain will end up receiving a high amount of pain signals, which may lead to change its normal functioning to accommodate this new scenario. Processing large amounts of pain signals will consume a lot of the brain's energy and power.
The brain will become specialized in this new task to an extent that pain processing will now be highly facilitated.
This means that it is »overly attentive « to pain which enhances the pain even more.
Brain orchestra and pain symphony
And what does that mean for the brain?
The brain works like an orchestra, with different areas being responsible for different functions (language, vision, attention, etc.).
All the areas work together for us to be able to act, think, remember, run, and do all the activities we need in our lives.
However, there is no such a thing as a unique pain brain area. Pain is perceived when several different brain areas are engaged in a certain rhythm, like an orchestra.
Exaggerated pain signals will change the synchrony in this orchestra. Some brain areas will be overused, some will be underused, and the final »symphony« may be out of tune.
A brain that is constantly processing pain will be less efficacious to learn, to pay attention, to sleep properly, to take fast and good decisions, and will be more likely to face mood symptoms. Even the ability to control pain may be disrupted.
Continuous pain also changes the way different brain areas connect with each other (called neuroplasticity), creating disconnection and loss of efficacy. A brain in pain will not only experience pain itself but will experience changes in function affecting most of its activities.
Center for Neuroplasticity and Pain (CNAP)
CNAP do forefront research to study basic characteristics of pain neuroplasticity in humans and how this can be modulated. Our research approach is to provoke, probe and modulate pain neuroplasticity in a dynamic, interdisciplinary and international research environment.
Examples of CNAP research have led to new ways to evaluate specific pain mechanisms in chronic pain conditions, as well as changes in brain function during prolonged pain.
CNAP was established as a Centre-of-Excellence by the Danish National Research Foundation in 2015.
So how do we treat chronic pain?
Since chronic pain affect so many different functions of the brain, its management is usually a combination of different types of treatment, something called multimodal treatment.
There is however no magic treatment, the existing chronic pain treatments is only working in some patients, and unfortunately there has been very few new innovative ways for management of chronic pain.
The main reason is that the exact mechanism in chronic pain is likely to be very individual and not linked to a specific disease.
Depending on the pain type, treatment may include medications, physical rehabilitation, psychotherapy, or mental health care, and in some instances even surgery.
Treatment is inefficient for 40 percent – so what do we do?
One big challenge for researchers, patients, and health care professionals, is that up to 40 percent of patients with chronic pain may remain symptomatic despite optimized pain treatment.
And we don’t know why.
Among the developing perspectives for pain control, we can mention the use of special coils placed over the scalp, the researchers can deliver weak electromagnetic pulses or low intensity electric fields to the brain (see here and here).
They do this to stimulate brain areas that are depressed by pain, or tune down the areas presenting overactivity, so that a new balance is achieved.
Another strategy is to try to boost our own bodies descending pain modulatory system by behavioral measures (for example better sleep quality and exercise etc.).
In short: Pain is present in our daily life and protects us.
But chronic pain is also the most prevalent medical condition, it leads not only to personal and family suffering but to high costs to society.
A more efficacious management of hard-to-treat pains is one of the big challenges neuroscientists currently tackle and we and other colleagues are working intensely to solve the problem.
If pain can get in the brain, it can also get out of it with proper management.
This article was originally published on our Danish sistersite, Forskerzonen.
- Daniel Ciampi de Andrade's profile (AAU)
- Thomas Graven-Nielsen's profile (AAU)
- 'Increasing prevalence of chronic non-cancer pain in Denmark from 2000 to 2017: A population-based survey', European Journal of Pain (2022). DOI: 10.1002/ejp.1886
- 'Modulation Of Experimental Prolonged Pain and Sensitization Using High-Definition Transcranial Direct Current Stimulation: A Double-Blind, Sham-Controlled Study', The Journal of Pain (2022). DOI: 10.1016/j.jpain.2022.01.012.
- 'Mechanisms and manifestations in musculoskeletal pain: from experimental to clinical pain settings', Pain (2022). DOI: 10.1097/j.pain.0000000000002690
- 'Extensive sensorimotor training enhances nociceptive cortical responses in healthy individuals', European Journal of Pain (2023). DOI: 10.1002/ejp.2057