How can prolonged pain change neurons in the spinal cord and brain?

Prolonged or chronic pain can induce significant physiological changes in the central nervous system, effectively sensitizing it and creating neuronal alterations that persist even after the initial injury has healed.1

Spinal Cord Changes

In the spinal cord, constant pain impulses increase the excitability of dorsal-horn neurons. This leads to a state where these neurons fire continuously and may begin responding to light touch, which would not normally trigger a pain response. This sensitization involves changes in the firing thresholds of interneurons located between afferent nerve fibers and motor neurons, resulting in prolonged reflex responses.2

Brain Changes

These states of increased sensitivity are transmitted to the brain, where they can alter the character of neurons in the thalamus and cerebral cortex. Eventually, cerebral neurons may generate impulses spontaneously and continuously, and other brain regions may begin responding to stimuli—such as movement in an affected joint—that would typically be ignored. Research has also identified specific enzymes, such as adenylyl cyclase types 1 and 8, that play a role in sensitizing the forebrain to pain stimuli.21