How Does Pain Work?

By guest blogger Dr. Damon Bescia DPT, OCS, SCS, FAAOMPT

What is Pain?

What is Pain?  Pain is an unpleasant subjective 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 a 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  While it may sound logical, this outdated model has fallen short on many fronts.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 into 6 common myths about pain:

Myth #1: “Pain receptors in my body convey the pain message to my brain.”

If this myth were true, 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],[2],[3]  Therefore, pain may be experienced even in the absence of any tissue in that area at all.

Myth #2: “Pain means tissue damage.  Therefore, when I have severe pain, it means I have severe tissue damage.”

This may sound reasonable, but it has been disproven in scientific studies several times over.[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[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.)

Additionally, this myth cannot explain why surgeries that successfully remove injured structures don’t always eliminate – or even improve – pain afterward.[16],[17]  Conversely, it cannot explain why sham orthopedic surgeries were just as effective as actual surgery in reducing pain and disability.[18]

Myth #3: “I’m always in pain, but I’m not aware of it at present because I’m just used to it.”

Pain is an unpleasant subjective 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.

Myth #4: “Chronic or persistent pain means that my injury hasn’t healed properly.”

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 "Subclassification of Chronic Pain".

Myth #5: “Pain is all in your head.”

It is true that pain is an 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 your 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:

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.

Myth #6: “I feel your pain!  I know how that feels!”

Despite good intentions, none of us can truthfully make that claim.  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.

Therefore, it’s impossible for two persons to experience the same pain.

So… What Is Pain?

As we have discussed, misconceptions about pain are prevalent.  But, they have fallen short of accurately explaining the true pain experience.  Arguably the most concerning fact is that an outdated and inaccurate theory of pain can lead to an increase in both pain and disability for individuals who persist in avoiding activity or certain movements out of fear of pain[20], and some well-intentioned health care providers unwittingly contribute to this increase by advising their patients to avoid certain activities altogether.

Therefore, we need to better understand pain.

Pain is an unpleasant subjective 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.

The truth is that there simply are no “pain fibers”; 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]

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.

You are likely to experience pain when spraining your ankle while playing a recreational sport; you are highly unlikely to experience pain when spraining your ankle while running from a tiger.  In the latter scenario, you likely wouldn’t be tremendously concerned about your ankle that just got tweaked, as you’d have a bigger threat to deal with in the 600-lb combination of speed, power, and teeth right behind you.  If you are fortunate enough to survive that encounter, you may eventually experience ankle pain once you’re able to calm down and compose yourself.  Ultimately, the level of perceived threat assigned to a given sensation determines whether or not you experience pain with it.

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],[23],[24]

If you are a health care provider who treats individuals in pain, you owe it to your patients to have an accurate understanding of pain and to promote a healthy approach to it without unwittingly contributing to increased pain and disability.  If you are a patient seeking relief from pain, it’s critical that you choose a health care practitioner who has an accurate and up-to-date understanding of pain and knows how to best treat it.  You're also invited to consider how a manual physical therapist treats pain.

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.  For more information, please visit www.NaperManualPT.com.







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