The Mayo Clinic Guide to Pain Relief by Wesley P. GIlliam, Ph.D., and Bruce Sutor M.D explains how pain develops, how it can become chronic, and what you can do to free yourself from chronic pain’s effects.
Scientific research continues to illuminate how pain is transmitted through the nervous system and how the experience of pain is created in the brain. One important discovery relates to a process called central sensitization. To understand this process, it helps to know a bit more about a unique quality of the brain called neuroplasticity.
The Ever-Adaptive Brain
Neuroplasticity means the brain structures and sensory pathways in your central nervous system can change and adapt in response to sensory input, to sensations and events you experience in your life.
This ability to change can be helpful. For example, taxi drivers in large cities have learned to navigate various roads and intersections, remembering maps and finding alternative routes. Over time, more areas of the taxi drivers’ brains become involved in processing information about what they see and understand. The taxi drivers’ brains become “hardwired” with many possible pathways to help them drive quickly and efficiently despite traffic and road construction.
Unfortunately, the brain’s ability to adapt also can be harmful. The central nervous system can change based on the type of information about pain coming from the senses. The brain can make more pathways to move pain signals more efficiently — too efficiently, in fact.
As the brain becomes faster at processing certain sensory signals, it becomes so sensitive that it can no longer accurately determine which sensory inputs indicate danger. So it makes more and more intense signals of pain and other uncomfortable sensations. This process is called central sensitization.
Sensitization and Pain
Sensitization is like the volume control on a radio becoming stuck on high. It amplifies sensory messages, making them stronger and, at times, distorted. People with a sensitized nervous system may experience pain in response to things that should not be painful (allodynia) or experience heightened levels of pain in response to things that previously only caused mild to moderate pain (hyperalgesia). In some cases, the pain spreads to other areas for no reason and symptoms such as fatigue, headaches, unrefreshing sleep and mood changes can occur.
Sensitization can result in constant nausea and vomiting, fatigue, motion sickness even at rest, constant dizziness or severe pain. When you have central sensitization, your brain overreacts to sensory signals, treating them as though they indicate danger and sounding the alarm with subsequent physical reactions.
Hyperexcitability of the central nervous system can occur even in the absence of sensory information coming from the peripheral nerves. What this means is that the brain and spinal cord can create symptoms by themselves.
An example of this is phantom limb pain. In this condition, a person can feel intense pain in the location of a missing body part – for instance, pain in an arm or a leg that’s been amputated. Phantom limb pain, which is difficult to treat, is explained by persistent activation (sensitization) of the pain transmission pathways. The injuired limb is no longer there, but the pathways in which pain messages were transmitted are still active.
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