After amputation, the brain's somatosensory cortex retains the neural representation of the missing limb. Within days to weeks, neighboring cortical regions begin invading the deafferented territory in a process called cortical reorganization. Research shows that the degree of this reorganization correlates directly with the intensity of phantom pain experienced by the patient.
At the spinal cord level, severed peripheral nerves form disorganized growths called neuromas that generate spontaneous electrical signals. These aberrant signals travel to the dorsal horn, where central sensitization amplifies the pain response. NMDA receptors in the spinal cord play a critical role in maintaining this heightened excitability, which is why NMDA-receptor antagonists like ketamine show particular promise for phantom limb pain.
The sympathetic nervous system further complicates the picture. Stress hormones such as norepinephrine can activate nociceptors at the neuroma site, explaining why emotional distress, weather changes, and physical fatigue often trigger or intensify phantom pain episodes.
