What The Heck Is Pain?

By Wendy Winn, PT, OCS

Pain is so individual. It’s felt and processed differently by everyone. But what causes pain in the short and in the long term? Why does pain become chronic?

Pain has many different elements and can broadly be described as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage.” 

Prior to the advent of neuroimaging of the brain, pain was thought to have solely originated from a pain source. That pain source, say a certain tissue, would show signs of reorganization and damage. The nerve pathway to and from the spinal cord could also show impairment. What has been missing in the understanding of how pain is processed in the brain. And, perhaps more importantly, how does pain become chronic, and what can we do about it?

Acute pain after an injury is the body signaling the brain for help. Once assistance is provided and the body heals its tissue, why does pain persist in some situations? There are many theories about chronic pain, with only proposals for answers. More research is needed on this complex issue, but researchers have recently shared new and important information.

Pain is not simply a mechanical sensory experience. In other words, you don’t just twist your ankle and feel the “ouch.” The pathways in the brain that allow you to feel the pain also aid in your ability to feel emotions, rewards, and they feed into the central nervous system (your autonomic fight or flight system). Often your experience of pain presents as an encoded feedback loop; a signature of your pain. 

During the encryption of the nervous system’s recording of your pain, many areas of the brain are illuminated on a functional MRI. These include the primary and secondary somatosensory cortices (senses warmth or pressure), the insular cortex (turns experiences into emotions), prefrontal cortex (thoughts and feelings), amygdala (survival instincts and memory), cerebellum (posture and balance), mesolimbic reward circuit (the dopamine pathway), and periaqueductal grey matter (pain suppression). All of these areas are associated with deeply seated emotions, instinctual responses, and autonomic functions. All this is to say that your experience of pain is primal.

So what goes wrong when pain doesn’t go away after treating the injury? Studies suggest that the glia (brain cells) and neurotransmitters (such as dopamine) become accustomed to receiving your pain signature, the encoded feedback loop that informs how you experience pain. The glia can get used to responding to the pain, and some researchers propose that even after the original pain source is removed, the brain will still look to reproduce it. This means that your brain is becoming addicted to the pain, even after your injury is healed.

How does this happen? We’re not sure yet, but researchers are looking for patterns and answers. There is a study suggesting that certain characteristics detected on functional MRI in the prefrontal cortex can be a predictor of chronic pain. A second study proposed a four step process of dysfunction within the feedback loop in the brain. 

So what do we do about it? Everyone processes pain differently and everyone has different neural circuitry. There are also layers of experience that are encoded with each interaction over time. Some researchers suggest that neurotransmitters, such as dopamine, may help to mitigate chronic pain, but there are many areas in the brain that may need attention. Some researchers propose using functional MRI on stubborn cases of chronic pain, which will hopefully lead to more clarity on how to treat difficult cases. 

Positive Emotions and brain reward circuits in chronic pain. Naratilova E et al. J Comp Neurol. 2016 June 1; 524(8)

The Emotional Brain as a Predictor and Amplifier of Chronic Pain. Vachon-Presseau E et al. Journal of Dental Research. 2016 Vol 95 (6)