The majority of humans have experienced pain in some way, although there are some people who don’t feel pain due to conditions like diabetes, leprosy or a spinal cord injury. While it may sound attractive to never experience pain, keep in mind that people who don’t have the ability to feel pain, can sustain significant injuries without realizing it. In this way, pain is a protective sensation.
It may seem obvious that if you hit your thumb with a hammer or stub your toe, you will experience pain. Hopefully, as the injury heals the pain will go away, but pain is not quite that simple.
The topic of pain is complicated, and there are many things about pain that are not well understood. Pain is unique to each person, but why is that? If two people hit their thumbs with a hammer, shouldn’t it feel the same for both? Why is a painful injury for one person not particularly painful for someone else? Are some people or groups just tougher or better able to tolerate pain? Why does pain persist for some people even though their original injury has healed? How do we even define pain?
The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”1 Pain is typically described as either acute or chronic.
Acute pain is usually a symptom of an injury or illness.2 It can be attributed to the healing process related to the injury and has been present for less than three months.
Pain is chronic if it lasts for more than three months and continues despite treatment to heal the original injury that caused the pain. Chronic pain can be thought of as a disease unto itself because it continues even after an injury has been treated and appears to be healed.2 Nearly 5.6 Million Canadians aged 18 and over,3 or 22% of the Canadian population,4 experience chronic pain.
Over the years, several explanations of how pain works have been presented.
One early theory suggested that specific nerves throughout the body sensed pain and connected to a part of the brain dedicated to receiving and interpreting pain messages.5 This part of the brain was thought to have a map that correlated to and received pain messages from the body.5 This theory has been discarded because scientists have learned there is no dedicated pain center, unlike parts of the brain dedicated to other sensations such as hearing or vision. The theory also does not explain why people have different pain experiences after the same injury.
Another theory proposed that the same nerves that carry the messages of touch or warmth also carry messages of pressure or heat that are perceived as painful.5 The pattern or strength of the message determined if it was interpreted as painful.5 But this theory didn’t explain differences in how pain is felt by different people, or pain that continues even after the painful input is removed, as is the case with chronic pain.
This led scientists to a new pain theory that could begin to explain why the same painful messages can be extremely painful for one person, and only mildly irritating to the another. This theory suggested that the brain can “select, filter and change pain signals.”6 Meaning a potentially painful message from the foot, for example, can be “turned up” or “turned down” by other nerve inputs from the brain and body.6 Unfortunately, this didn’t explain why pain can continue even after injuries have healed.
The neuromatrix theory builds on these earlier theories, helping to explain chronic pain and furthering our understanding of why pain is perceived differently by different people. The theory suggests that a group of connected nerves in the brain (the neuromatrix) create patterns that we interpret as pain.6 This collection of nerves and the patterns they create are influenced by messages from the body as well as our thoughts, emotions and past pain experiences. These inputs can make the neuromatrix easy or difficult to trigger6 – which helps to explain people who claim they have a high “pain tolerance.” This also means that what happens in muscles, bones and joints are only partly responsible for a person’s experience of pain.6
This theory also suggests that:
Pain can happen without input from the body. (An example is phantom limb pain where a person with an amputated limb can still feel the limb.)6
Bones, muscles and joints do not send pain messages to the brain. Instead, they send danger messages. Thus, it is the brain, not the body, that determines the pain we perceive.6,7
Over time, the neuromatrix can become hypersensitive. In other words, changes to this group of nerves can mean that messages not usually felt as pain become painful.7 This hypersensitivity or ongoing activity within the neuromatrix can explain pain that continues even after an injury has been treated and resolved. It also explains differences in how two people perceive the same uncomfortable message.
Messages from the brain, including psychological factors, can impact the neuromatrix’s patterns and the likelihood of developing chronic pain. These factors could include depression, fear of pain, the meaning people assign to pain, and the way people manage or cope with their pain.7,8 When people are unhappy, stressed or believe pain is a punishment, it becomes more threatening and they are more likely to develop chronic pain.
When people have low levels of stress and believe they can manage their pain, it becomes less threatening. They are less likely to experience chronic pain and are better able to manage their pain. When people believe their pain relates to an ongoing threat or injury, it is more likely to persist. When they understand that tissue injury is only a small part of what we know as pain, it becomes easier to move and increases the person’s control over their pain.
Ultimately the experience of pain, both acute and chronic, is the result of a complicated interaction between real or perceived tissue injury and the thoughts, feelings, past experiences, and beliefs of the person affected.2,7
So, it’s all in my head?
Well no, but sort of. When people say that pain is “all in your head,” there can be an implied judgment that the pain isn’t real and therefore isn’t important. Neuromatrix theory suggests that a complex group of nerves and the way they interact with each other, with your thoughts and feelings, and with messages from your body (both comfortable and uncomfortable) determines how you experience pain. That interaction happens in your head, but in no way suggests pain isn’t real. All pain experiences are real and important.
Hope for people in pain
For physiotherapists working with people in pain, the natural response is to remove the cause or heal the injury to ease the pain. Many physiotherapy treatments seek to do exactly this. While this approach can work well when treating acute pain, it is less effective when attempting to address chronic pain.
When working with people with chronic pain, a different approach is needed. Instead, treatment focuses on educating people about pain and its meaning and determining the physical, psychological and social factors involved in their pain. A management plan can then be made to address all of the factors influencing the pain. Physiotherapists have unique knowledge and skills to help people with chronic pain to set an appropriate level of activity and gradually increase activity within their tolerance. This approach reduces pain flare-ups, helps gradually increase tolerance to movement, and helps people with pain return to doing the things they like to do.7
International Association for the Study of Pain. IASP Taxonomy. Available from http://www.iasp-pain.org/Taxonomy#Pain Accessed on August 18, 2016.
George, S. 21st John H.P. Maley Lecture: Pain Management: Roadmap to revolution. [Lecture] American Physical Therapy Association Next Conference. Nashville. June 8-11, 2016. Available at http://www.apta.org/NEXT/2016/MaleyLecture/ Accessed on August 18, 2016.
Statistics Canada. Study sample and percentage distribution of selected characteristics, household population aged 18 or older with chronic pain, Canada, 2011/2012. Available from http://www.statcan.gc.ca/pub/82-003-x/2015001/article/14130/tbl/tbla-eng.htm Accessed on August 18, 2016.
Gilmour, H. Chronic pain, activity restriction and flourishing mental health. Statistics Canada 2015. ISSN 1209-1367. Available from http://www.statcan.gc.ca/pub/82-003-x/2015001/article/14130-eng.htm Accessed on August 18, 2016.
Physiopedia. Theories of Pain. Available from http://www.physio-pedia.com/Theories_of_Pain Accessed on August 18, 2016.
Melzack, R. From the gate to the neuromatrix. Pain 1999; Supplement (6):S121-S126.
Wideman, T & Bostick, G. Chronic, Complex Pain-What can I do in 15 minutes. [Webinar] Physiotherapy Alberta. May 12, 2016. Available at https://www.physiotherapyalberta.ca/xchange/continuing_professional_development/elearning_center/chronic_complex_pain_what_can_i_do_in_15_minutes?course_type%3Alist=Recorded+Webinar Accessed on August 18, 2016.
Mosely, G.L. A pain neuromatrix approach to patients with chronic pain. Manual Therapy 2003; 8(3):130-140.