We have learned more about pain science in the last ten years than we have in the last hundred. Progressive and rapid research from the fields of neuroscience, physical therapy, and psychology have slowly but steadily unearthed the mystery of how the brain is the “head honcho” when it comes to pain. You see, your brain is constantly changing, based on your environment and the input it receives. This concept is known as neuroplasticity, or simply plasticity. The term neuroplasticity is derived from the root words neuron and plastic. A neuron refers to the nerve cell and its various parts, such as axon, dendrites, and the small space linking two nerves called the synapse. The word plastic means “capable of being molded, sculpted, or modified.” Neuroplasticity is your brain’s potential to reorganize by creating new neural pathways and adapting as needed. Plasticity was a wonderful finding when it was first discovered, because it informed us that our brain had the potential to learn right into old age, right to the very last day. We now know it is never too late to acquire new abilities, such as a language, dancing, or singing.
As you use your brain to learn additional skills, neurons will grow, sprouting new connections that enable you to grasp the coordination necessary to learn the cha-cha, articulate a new phrase, such as “¿hola, como estas?” while on vacation in Mexico, and carry a tune while singing in the shower. We have seen this type of science applied to those who have suffered a traumatic brain injury, where parts of the brain have been severely damaged. Other areas of the brain will take over, and neurons will begin to sprout new connections used for relearning activities that were once automatic. The concept of neuroplasticity — and the ability of the brain to reorganize itself in both structure and function — is truly remarkable. For example, people who are visually impaired can engage their visual cortex for fine sensory discrimination when using their hands. In these situations, neuroplasticity appears to be a positive adaptation to loss of function. With pain, however, plasticity seems to go a bit awry.
While your brain has amazing capabilities for adaptation and growth, it takes into account many different factors when deciding to create a pain response — and all of these signals can have an impact on its decision and interfere with neuroplasticity. For example, during your pain experience, your brain also receives information connected to that experience, such as your thoughts, memories, movements, sensations, emotions, sights, smells, and so on. All of these factors have an influence on your brain’s decision to create pain. Essentially, pain is an experience your brain has created based on past experiences, upbringing, cultural influences, thoughts, emotions, your environment, and your current stress level. With persistent pain, these factors are continuing to affect your brain’s decision to create pain, and they are interfering with your healing. For example, if you often have negative thoughts or are consumed by fear, anger, and guilt, your brain will continue to create a pain response long after your initial injury.
Understanding neuroplasticity has put an end to the old worldview of pain as simply a sensation transmitted along hard-wired paths up and into the brain. Neuroplasticity occurs in your brain as an attempt by your central nervous system (brain and spinal cord) to adapt to injury in a positive way. But in the case of persistent pain, neuroplasticity can be maladaptive and at times work against those trying to cure themselves from pain. Your brain is a large receiver, kind of like a satellite up in space that is constantly receiving signals. Satellites can receive signals from the numerous cell phone towers below on Earth. It is a satellite’s job to receive information from the various places, decipher the information, and then transmit a signal. Your brain is similar to that satellite, because it is constantly receiving information. Nociceptive input sends danger signals from your skin, joints, and muscles to be interpreted by your brain. For example, if you sprain your ankle, information about an injury will be sent to your brain. However, this is far from the only information your brain is receiving and processing. At the same exact time, your brain is also receiving visual input via the optic nerve in your eyes, smell from olfactory nerves in your nose, sound from your auditory nerve, and even taste from your lingual nerve on your tongue.
It does not stop there; your brain is also cross-checking the information it has previously stored to weigh in on its decision. Stored information about pain, in the form of memories, as it relates to past experiences as well as beliefs and cultural influences also significantly contributes to the brain’s present decisions. And issues such as stress, anxiety, post-traumatic stress disorder (PTSD), or depression can contribute even more input. Combine all of this data, along with lifestyle factors (nutrition, weight, sleep), and your brain has quite a job on its hands. This matrix of information is considered by the brain and occurs in a millisecond! These are just some of the multitude of factors your brain considers before pain is created. If your brain receives enough danger signals from the variety of inputs it receives, it will trigger the alarm and your brain will create pain. This is why different people have different amounts of pain, even with similar injuries, or why your pain can change from day to day. It can also help explain why pain fluctuates throughout the day, with stress (such as when you argue with a spouse or have a deadline at work) or when fear kicks in (at the dentist!). The brain creates pain based on many factors. How much pain your brain creates is based on how many danger signals it receives from the various inputs as well as how “sensitive” your nervous system has become.
An oversensitive nervous system
Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain. When central sensitization occurs, the nervous system is in a persistent state of high reactivity. This constant state of reactivity will maintain pain even after the initial injury might have healed. How do you know whether your symptoms of pain are due to an oversensitive nervous system? The changes of central sensitization occur after repeated experiences with pain. First, identify whether you have any type of inflammatory or metabolic disorder or disease, such as autoimmunity, diabetes, metabolic syndrome, insulin resistance, heart disease, or other tissue pathology. If you fall into one of these categories, Chapter 6, “Gut Healing,” (in the book Heal Your Pain Now) will be your launching point to heal your pain, as well as incorporating regular healthy movement into your life. However, it is important to note that if you have struggled with these diseases for years, resulting in fear of movement, anxiety, or depression, then central sensitization is likely a contributing factor — even with a disease process that can cause tissue destruction.
Recent studies in the Journal of Rheumatology have implicated central sensitization in those with rheumatic diseases and autoimmunity, such as multiple sclerosis, autoimmune thyroiditis, rheumatoid arthritis, fibromyalgia, Sjögren’s syndrome, and many others. If you do not have inflammation and you are well past the stages of healing (three months), it is likely central sensitization is causing your persistent pain. Increasingly, research is demonstrating how the brain clearly plays a role in many different chronic pain disorders. It can occur with chronic low back pain, chronic neck pain, whiplash injuries, chronic tension headaches, migraine headaches, osteoarthritis, endometriosis, injuries sustained in a motor vehicle accident, and following surgeries. Fibromyalgia, irritable bowel syndrome, pelvic pain, interstitial cystitis, and chronic fatigue syndrome all have central sensitization as a common denominator as well.
Central sensitization has two main characteristics; both involve a heightened sensitivity to pain. The first is allodynia, which is when a person experiences pain with things that are normally not painful like a simple touch or massage. In such cases, the sensation of touch travels, of course, through the nervous system. Because the nervous system is in a continual state of heightened sensitivity, the sensation is registered in the brain as painful or uncomfortable, even when it really shouldn’t be. The second is hyperalgesia, which occurs when an actual painful stimulus is perceived as more painful than it should be. An example might be if someone pinches your arm, which ordinarily would be mildly painful, and it sends you through the roof with pain. Again, the sensation of pain travels through the nervous system, which is in a constant state of high sensitivity, and the pain is registered in the brain as a heightened level of pain. If you are more than three months past an injury (tissue damage) and you are still having persistent pain, there is a good chance your nervous system has become overly sensitive.
Want to learn more about the brain’s relationship with pain? Read “Chronic Pain Amplifies the Brain’s Reaction to New Injuries” and “Can Pain Be Controlled by the Brain?”