How Does Pain Work and Why Do We Hurt?
As featured on PT-Helper
What is Pain?
Pain is an unpleasant sensory experience generated by an individual’s unique pain neural signature that may be activated either spontaneously or when a stimulus is perceived as a threat.
Why Learn About Pain?
Erroneous ideas about pain abound among patients and health care providers alike. If you are seeking relief from pain, understanding pain is a very important step on your way to recovery. If you are an orthopedic manual physical therapist or other health care provider who treats patients in pain, you owe it to your patients to 1) have a correct understanding of pain and 2) be able to explain it accurately in plain language to your patients.
Misconceptions About Pain
Many understand pain to work like this: “Pain fibers throughout the body send pain messages from an injured body part up to the brain so that a person will do something to eliminate the pain.” While it may sound logical, this outdated model has fallen short on many fronts.
Let’s break it down:
Do pain receptors in the body send the pain signal to the brain?
No, there are no pain receptors; there are only “nociceptors”. These terms are not synonymous. Nociceptors are nerve cells that transmit sensory information – not pain – to the brain via the spinal cord for processing. Nociceptors do not perceive, produce, or transmit pain. Pain is experienced only after the sensory input is sent to the brain, processed by the pain neuromatrix, and is determined to be a threat. [21]
If pain came from pain receptors in the body, phantom limb pain wouldn’t exist. However, 90-98% of individuals report experiencing phantom sensations in a limb following its amputation – the majority of them reporting distinct pain. [1-3] Therefore, pain may be experienced even in the absence of any tissue in that area at all.
Does pain mean tissue damage?
Pain does not always mean tissue damage. This has been proven in scientific studies several times over. [4-15] Many people have injured tissue such as bulging discs, arthritis, labral tears, tendinopathy, degenerative changes, muscle tears or ruptures, etc without any pain at all. Others have incapacitating pain without any tissue damage at all. Pain is not simply “an issue of the tissue.” Tissue injury can occur without pain, and pain can occur without injury. (You're also invited to consider the inability of X-ray, MRI, and CT Scan findings to explain the patients' pain.)
If pain always means tissue damage, phantom pain wouldn't exist. Along the same lines, why do some surgeries that successfully remove injured structures fail to eliminate – or even improve – pain afterward? [16-17] Even some sham orthopedic surgeries were just as effective as actual surgery in reducing pain and disability. [18]
Can you be in constant pain and not be aware of it?
No, pain is an unpleasant sensory experience. Therefore, you cannot be in pain without being aware of it. For instance, no pain is experienced during surgery despite the extensive bombardment of sensory information because anesthesia removes the conscious component of the experience.
Does chronic or persistent pain mean that the injury hasn’t healed properly?
No. Injuries heal in predictable stages, and even slow-healing tissues such as herniated discs have been shown to heal over time. [19] Most tissues heal within weeks. However, some pain experiences last for months or even years. Further, many individuals have chronic pain with no history of injury. Typically the longer the pain lasts, the less important tissues are and the more important a sensitive nervous system is. For more information, you're invited to read my blog on chronic pain.
Is pain all in your head?
It depends what is being asked. It is true that pain is a subjective experience produced by the brain - with or without contribution from the body. However, the phrase "pain is all in your head" inaccurately and insensitively implies that pain is imaginary. Additionally, chronic pain may be due to a series of physical changes that happen over time called "central sensitization". While learning about the scientific explanation may not be for everyone, simply understanding that your pain is not “all in your head” can be very liberating. For those intrigued by the physiological explanation of chronic pain, this is for you:
What is central sensitization?
Central sensitization is defined as "an increased responsiveness of nociceptors in the central nervous system to either normal or sub-threshold afferent input." [25] Central sensitization results in hypersensitivity to stimuli, responsiveness to non-noxious stimuli, and increased pain response evoked by stimuli outside the area of injury. How do these changes happen physically?
It appears that the chronic bombardment of C-fiber activity into the dorsal horn results in permanent changes over time, killing off the interneuron with high levels of amino acids, and allowing more information to be passed onto the spinal cord and brain. As C-fibers pull back and A-fibers grow into the dorsal horn, light touch fires more easily into the spinal cord and leads to increased sensitization and decreased endogenous mechanisms, leading to allodynia or hyperalgesia. Chronic retrograde firing may result in inflammation, swelling, and immune responses.
Can you know how another person's pain feels?
No, no one can know how another person's pain feels. That is because each pain experience is dependent on a unique combination of each person’s experiences, beliefs, knowledge, logic, social behavior, anticipated consequences, mental state, emotional state, financial concerns, sensory cues, anticipated outcomes, fears, environment, and more. A typical pain neural signature commonly involves a map of these 9 areas of the brain:
Amygdala – responsible for processing and memory of emotional reactions, fear, fear conditioning, addiction.
Primary Somatosensory Cortex – involved with somatic sensation, visual stimuli, movement planning.
Hippocampus – performs consolidation of info from short-term to long-term memory, spatial navigation, memory, fear conditioning.
Anterior Cingulate Cortex – regulates blood pressure and heart rate, assists with reward anticipation, decision-making, empathy, emotion, and concentration.
Primary Motor Cortex – assists with planning and executing movements
Hypothalamus – regulates body temperature, hunger and thirst, fatigue and sleep.
Thalamus – plays a role in consciousness, sleep, alertness
Prefrontal Cortex – moderates personality expression, decision-making, social behavior, memory.
Cerebellum – facilitates movement, balance, proprioception, coordination, cognition, and fear.
It’s impossible for two persons to experience the same pain.
The amazingly complex neural signature located in your brain ultimately determines when you experience pain, and the body may or may not be involved in the process. For a sensation to become painful, you must perceive it as a threat. Further, the nervous system is a dynamic and living organism driven by thought and emotion, and it is very closely linked to the immune and endocrine systems. Therefore, cognitions such as fear, anxiety, and catastrophization are strongly correlated to the pain experience as they are to overall health and wellbeing. [22-24]
How can I get relief from my pain?
If you are a patient seeking relief from pain, it may be helpful to choose a physical therapist or other health care professional who has an accurate and up-to-date understanding of pain and knows how to best treat it.
Further Information on Orthopedic Manual Physical Therapy
Click on any of the following links for more information:
Would you like a brief overview of the basics of orthopedic manual physical therapy?
Are you curious about the scientific mechanisms behind how orthopedic manual physical therapy works?
Do patients need an MRI or X-ray before beginning physical therapy?
What should you consider when choosing a physical therapist for an orthopedic condition?
What's an evidence-informed approach to the examination and treatment of sacroiliac joint pain?
How should one perform manual therapy for spondylolisthesis?
Dr. Damon Bescia is a fellowship-trained Doctor of Physical Therapy, board certified in orthopedics and sports physical therapy, who specializes in Orthopedic Manual Physical Therapy and serves Naperville and its surrounding communities by way of his Concierge Practice, providing private one-to-one orthopedic manual physical therapy for his clients. For more information, please visit https://www.napervillemanualphysicaltherapy.com.
