According to the Centers for Disease Control and Prevention, in 2021, the prevalence of chronic pain among U.S. adults ranged from 20.5% to 21.8%. With such a large subgroup of the population persistently in pain, let’s discuss what happens to our brain when we experience pain.
When our bodies experience pain, there are four steps that occur: i) transduction, ii) transmission, iii) modulation and iv) perception. The first step - transduction - is where the peripheral tissue (i.e. Skin) feels a mechanical sensation (i.e. Heat via the nociceptors). The second step - transmission - is where the sensation is passed through to the central nervous system via the axon of the nociceptors in the spinal cord and through to the brain. The third step - modulation - is where the brain alters the intensity of the signal depending on the circumstance one is in. Truly an evolutionary gift, this allows us to survive circumstances where we cannot afford to react to pain as it is. For example, if you were running from a mountain lion and broke your toe, you would be able to ignore the pain and keep on running until the threat was cleared. Pain perception is modulated at several areas in the brain including the dorsal root ganglion, the spinal cord dorsal horn, the reticular system of the brainstem, and the cortical areas of the brain. Finally, the fourth step - perception - is where we actually interpret and experience the pain in the cortex of the brain.
In light of the above, pain is clearly not just an objective processing of a stimulus. It is dependent upon neural processing in the spinal cord and several brain regions; it’s more than a pattern of nociceptive action potentials (when a neuron sends information down an axon). Action potentials ascending the spinothalamic tract are decoded by the thalamus, sensorimotor cortex, insular cortex, and the anterior cingulate to be perceived as an unpleasant sensation that can be localized to a specific region of the body. Action potentials ascending the spinobulbar tract are decoded by the amygdala and hypothalamus to generate a sense of urgency and intensity. Combined, they integrate sensations, emotions, and cognitions, resulting in our perception of the pain. This is good news because it means we can train ourselves to experience less pain as it is not purely a mechanical process, but rather an emotional and cognitive one too.
When we are referring to chronic pain (pain persisting beyond 3 months), however, this is another subject altogether. Individuals with chronic pain develop changes in their brain and nervous system over time. The signal pathway to the brain can become hyper-sensitized and hyper-reactive, whereby the persisting pain and emotional reaction to it creates a compounding effect leading to a vicious cycle that categorically causes a neurological disorder. These changes cause the brain to continuously send out pain signals even when there are none. Besides the persistence of pain, individuals with chronic pain can develop hyperalgesia (extreme sensitivity to pain). This occurs when the body's pain receptors become damaged or sensitized. This is why an antidepressant is often prescribed to chronic pain patients as the neurochemistry within chronic pain patients is usually altered in comparison to those without.
In addition to neurochemical changes in the central nervous system, studies prove that chronic pain causes regional brain atrophy, namely to the aforementioned regions. Correspondingly, it cause changes to one’s neurocognitive functioning. A study by the VA San Diego Healthcare System found that individuals with chronic pain show deficits in attention, working memory, learning and memory, processing speed, and executive function. These findings have been repeated by numerous other studies around the world. Chronic pain can also interfere with our daily activities (i.e. Working, physical activities and social activities) and lead to depression, anxiety, and trouble sleeping; all of which could further exacerbate the problem. This tells us that not only does chronic pain affect neural pathways, but it also affects our neuropsychiatric functioning.
Since pain is an unobvious symptom, one that many find difficulty empathizing with, by understanding what happens to one’s brain when they experience pain (and chronic pain specifically) the hope is that more compassion is extended to those struggling with these types of pain. It’s a condition that undoubtedly changes one’s neurophysiology, with specific impacts on the central nervous system, brain functioning, and emotional wellbeing over time. So the next time you encounter a family member, friend, or coworker that struggles with back pain, arthritis, or neuropathy, take a moment to reflect on the toll this has taken on their mind, body, and brain and perhaps offer some consideration.
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