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Pain and the brain

Why is it that we drop to our knees and hold our ankle just after we twist it on the football field? Why do we violently flick and shake our hand after our opponent has just stepped on it with his metal cleats in the ruck of a rugby game? The same response happens when we burn our hand. Does pain just make us do strange things? Actually, there is method to our madness when we shake that hand. We are trying to dull the pain sensation, and there is a scientific explanation for our antics! There are a few theories about how exactly we feel pain, but one of the most accepted is called the Gate Control Theory of Pain. It is far more complicated than what I will attempt to explain, but simply put this theory describes a gating mechanism in the spinal cord. There are two types of receptors in the spinal cord: pain receptors, which transmit painful sensations, and then our normal receptors which transmit normal sensations that we feel when things touch us. Both of these receptors connect to the brain through a “gate.” When Jean is walking in an empty space there is no input from either the pain or the normal receptors; the gate remains closed so no message is transmitted to the brain and therefore Jean feels no pain. If Dinah then comes along and just brushes past her, Jean’s normal tactile receptors are stimulated, the gate still remains closed, and Jean feels no pain, just simply Dinah’s touch.

However, if Rosita meets Jean in a crowded room and pushes her way through elbowing Jean in the face, Jean’s pain receptors are activated, and the gate opens, sending messages to the brain that she interprets as pain. She may react by rubbing her face. This action, as strange as it may seem, actually triggers the normal tactile receptors. The stimulation of these receptors can over-ride the input from the painful receptors and close the gate so that messages of pain do not get to the brain. She then no longer feels the pain, or is able to dull the sensation. This is the same reason why the football player grabs her ankle after a tackle or that rugby player shakes his hand after is has been stepped on. However, despite painful stimuli reaching our brains from activation of our pain receptors, in some instances we can actually ignore it and it becomes less painful for us. This speaks to the great influence our brain has on our perception of pain. The power of our brain and thoughts also explains why in some research studies, those people given placebo drugs report a decrease in their pain. This cerebral influence also explains what is called psychogenic pain, or pain without any physical cause. Physiological and psychological factors affect our perception of pain. For example, brain circuitry degenerates with age so older individuals tend to have lower pain thresholds.

Women tend to have a higher sensitivity to pain (although some say we can tolerate it much better) than men. This may be due to hormonal influences and also sociocultural factors that dictate that men should be strong in the face of pain. When we are fatigued or stressed, or are deprived of sleep, we tend to experience more pain. Our emotions and memory also affect the circuitry of our pain pathways and can control how we perceive pain. How we have experienced pain in the past can dictate how we experience it today. For example, 45 year-old Clementina, who had an excruciating episode of low back pain after lifting a bucket of water during her job as a janitor, may continuously expect pain with lifting activities, and thus self-impose activity restrictions because she expects that she will get pain and experience it as severely as she did in her first episode, even though she may not. Here we see the behavioural component of pain, which can become vague and chronic in character, even if the injury has healed. This is another example of psychogenic pain, or as we say “it in she head!” In fact it is in her head! It is not that Clementina is not experiencing pain and is dishonestly reporting the presence of pain. It is actually how her brain perceives the messages it is receiving from her body in the context of her environment. She may actually be experiencing pain even though there is no longer any evidence of her injury.

This pain can become psychosocial in origin if Clementina receives sympathy from her friends, and attention from her very busy and emotionally distant husband. Furthermore, she may receive monetary compensation from her job, which will facilitate her pain behaviour as she has financial gain. It is operant conditioning in action! This kind of pain is usually unresponsive to physiologic intervention and requires psychological management. Pain is a highly subjective phenomenon, and has multiple factors that affect how an individual experiences it. Not only is it physical or sensory in nature, it has behavioural, social, verbal and even financial components. All too often we treat the diagnosis and fail to understand why pain continues despite resolution of the injury. We are often quick to accuse someone of “fakin d pain,” without consideration of their unique experience. When addressing pain, it is therefore vital that we view the entire person, and not just that person’s diagnosis.

This article is well written. The experience of pain is complex and we are all wise to understand that we should not minimize the factors that perpetuate it.

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