Three Facts That Will Change How You Think About Pain

 

Pain is described by many as a hurtful experience related to tissue damage, but stopping at that would only explain a small aspect of this complex experience. Rather, it is better to think of pain as the ultimate output. It scrutinizes multiple inputs including but not limited to hurt or damage. We now understand that emotional state, memories of past experiences, context, body location, and cultural beliefs are also relevant inputs. The combination of these is often required to create something deemed as pain and it is explained best by Melzack’s Neuromatrix Theory of Pain. His theory describes pain as being comprised of three domains. The somatosensory domain involves the sensation that our nerves pick up and send to our brain for processing.¹ The cognitive domain deals with the meaning behind the pain, and relates it to past experiences as well as potential solutions.¹ Lastly, the emotional domain relates to the attitude you have towards your pain.¹ Keeping these things in mind, here are three facts that will completely change how you think about the experience we call pain:

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1. Hurt Does Not Always Equal Damage

A recurring theme regarding the perception of pain is that hurt equates to the level of damage someone is experiencing. However, what if you have an awful onset of lower back pain but then an X-ray and MRI turns up negative? Surprisingly or not this is a common finding in literature for many injuries, just take a look at this talk by Peter O'Sullivan, professor of musculoskeletal physiotherapy at Curtin University. Pain is too complex of a phenomenon to be able to say that if “x” amount of damage occurred to your tissue, then “y” amount of pain will be experienced. Nociception, which is the perception of harm or tissue damage is only one input. It is not always sufficient for a pain experience to occur. As we just mentioned, pain scrutinizes several relevant inputs along with nociception including emotional state, past experiences, context, body location, and cultural beliefs. For example, you can have tissue damage after an injury but if you do not pay attention to it nor are you in constant fear of it, then can it really be painful? What we do know about pain is that it is a helpful message the brain receives about our bodies from a biological standpoint. Pain gives us information about the healing state after an injury and warns us to avoid certain things that can cause more harm. These adaptive features of pain are important during the acute (early) phases of an injury. When pain becomes chronic (lasting more than 3 months), it loses its adaptive qualities. Chronic pain is an impairment that can affect one’s ability to function in normal activities. Interestingly enough, it almost always has a strong psychosocial influence.

Click page 2 to read about how chronic pain and depression are biologically linked

2. Chronic Pain and Depression are Biologically Linked

The reward circuitry of the brain has been long studied for its role in reinforcing behaviors, drug abuse, and most relevant to our current topic, mood disorders. It is controlled by the mesolimbic system. Its primary role is to produce and transmit the neurochemical dopamine from the ventral tegmental area (VTA) to the nucleus accumbens (NAc). Dopamine, also known as the reward chemical, is released when you eat good food, use recreational drugs, score during a game, solve a puzzle, you name it. Its release gives you a sense of reward any time you accomplish a goal or do something highly desirable. Dysregulation of dopamine in the mesolimbic circuit has been linked to mood disorders like depression and anxiety. Chronic pain can also dysregulate the mesolimbic system, particularly in the VTA-NAc dopaminergic pathway.² Its dysregulation can attenuate dopamine transmission, changing the reinforcing properties of reward-type stimuli to the individual. The brains of mice with chronic pain release less dopamine after they are given drugs like cocaine and morphine (drugs known to stimulate dopamine release).² On top of that, they also exhibit less reward-related behaviors such as spending more time in chambers where the drugs were present.² Individuals with depression also express less reward-related behaviors. These effects in mice solidify the link between chronic pain and depression.

The mesolimbic dopaminergic pathways are also responsible for the salience circuitry in the brain.³ Salience is the importance our brain gives to a certain stimulus or physiological state. In the context of pain, salience can magnify pain as well as minimize it. It can be attributed to why we can experience pain from emotional trauma in the absence of physical damage and how we can attain robust analgesic (pain-relieving) effects from placebo (inactive) treatments. We already know that chronic pain can dysregulate dopamine transmission in the mesolimbic system. The salience value for a given sensory input can also become abnormal due to alterations in the brain structures involved in this system.⁵ Essentially, in the same way chronic pain can affect our mood it can also affect how we evaluate our pain.

Click page 3 to read about how certain weather conditions induce more pain

3. Certain Weather Conditions Induce More Pain

For centuries, the link between a physical ailment and weather conditions have been talked about without any real confirmation. Many feel puzzled as to why certain weather conditions cause more pain. It’s a common complaint by those with arthritis, healed fractures, or migraines to name a few conditions. We know that people who are better informed about their pain tend to do a better job in coping with it. Yet little has been done to verify these complaints and explain them from a physiological standpoint. So here is what we do know:

Low atmospheric pressure has a significant association with pain. It is correlated with an increase in pain intensity in the period following acute or chronic fracture treatment.⁴ A strong association was also found in patients with osteoarthritis.⁵ Low atmospheric pressure often precedes stormy conditions which is why many individuals with arthritis or healed fractures report that they can sense when a storm system is coming before it even happens. It was initially thought that cold temperatures may also correlate with pain, but there was no association found. The analgesic effects of cold on inflammatory pain could be one reason why – just think about why we decide to put ice on a sprained ankle for example. In terms of a biological mechanism behind this phenomenon, we currently do not know. The inner ear organ and vestibular nerve in mice play a role in sensing changes in barometric pressures but further research is needed to clarify why this happens.⁶

Click page 4 to read a summarized list of all the links between depression and pain based on literature

Summary of the Links Between Depression & Pain from Literature:

• Certain antidepressants are prescribed as pain killers
• The comorbidity between depression and patients with chronic pain syndromes is high.⁷
• Pain avoidance can lead to continual withdrawal from activities and eventual depression.
• Negative emotional experiences can cause the sensation of pain in the absence of tissue damage.³
• Cognitive processes like expectation can modulate the effectiveness of analgesia
• Depressed chronic low back pain (CLBP) patients had higher levels of pain compared to CLBP patients without depression.⁸ Work and activity impairment was twice as high in the depressed individuals.⁸
• Opioid-stimulated and total striatal dopamine (DA) release levels are reduced in animal models of chronic pain, suggesting a neurological link to depression.⁹

References:

1. Melzack R. Pain and the Neuromatrix in the Brain. Journal of Dental Education. 2001;65(12):1378-82.
2. Taylor A et al. Microglia Disrupt Mesolimbic Reward Circuitry in Chronic Pain. Journal of Neuroscience. 2015;35(22):8442-8450. doi:10.1523/jneurosci.4036-14.2015.
3. Borsook D, Edwards R, Elman I, Becerra L, Levine J. Pain and analgesia: The value of salience circuits. Progress in Neurobiology. 2013;104:93-105. doi:10.1016/j.pneurobio.2013.02.003.
4. Shulman B, Marcano A, Davidovitch R, Karia R, Egol K. Nature’s wrath—The effect of weather on pain following orthopaedic trauma. Injury. 2016;47(8):1841-1846. doi:10.1016/j.injury.2016.05.043.
5. Figueiredo ECQ, Figueiredo GC, Dantas RT. Influence of meteorological elements on osteoarthritis pain: a review of the literature. The Brazilian Journal of Rheumatology. 2011; 51(6):616-628.
6. Funakubo M, Sato J, Obata K, Mizumura K. The rate and magnitude of atmospheric pressure change that aggravate pain-related behavior of nerve injured rats. International Journal of Biometeorology. 2010;55(3):319-326. doi:10.1007/s00484-010-0339-8.
7. Asmundson GKatz J. Understanding the co-occurrence of anxiety disorders and chronic pain: state-of-the-art. Depression and Anxiety. 2009;26(10):888-901. doi:10.1002/da.20600.
8. Tsuji T, Matsudaira K, Sato H, Vietri J. The impact of depression among chronic low back pain patients in Japan. BMC Musculoskeletal Disorders. 2016;17(1). doi:10.1186/s12891-016-1304-4.
9. Massaly N, Morón J, Al-Hasani R. A Trigger for Opioid Misuse: Chronic Pain and Stress Dysregulate the Mesolimbic Pathway and Kappa Opioid System. Frontiers in Neuroscience. 2016;10. doi:10.3389/fnins.2016.00480.