And when there is new sensory input, the pain memory trace in the brain magnifies the feeling so that even a gentle touch can be excruciating.
"Perhaps the best example of a pain memory trace is found with phantom limb pain," suggests McGill University neuroscientist Terence Coderre.
"Patients may have a limb amputated because of gangrene, the patients continue to feel they are suffering from pain in the absent limb," he said, according to a McGill statement.
Recent work has shown that the protein kinase PKMzeta plays a crucial role in building and maintaining memory by strengthening the connections between neurons (nerve cells).
Now Coderre and his colleagues have discovered that PKMzeta is also the key to understanding how the memory of pain is stored in the neurons. They were able to show that after painful stimulation, the level of PKMzeta increases persistently in the central nervous system (CNS).
Even more importantly, the researchers found that by blocking the activity of PKMzeta at the neuronal level reverses the hypersensitivity to pain that neurons develop after irritating the skin by applying capsaicin -- the active ingredient in hot peppers.