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Last updated: Wed, Mar 5, 2025
The gate-control model captures the way in which innocuous stimulation can suppress intense stimulation, through the interaction of small- and large-fiber inputs. Excitatory input comes from neurons at the center of a receptive field, while inhibitory input comes from neurons at the edge of the area of injury. This provides a sensory contrast and highlights the area of concern.
Conditioned pain modulation (CPM) is a related process, in which noxious stimulation to one area of the body reduces the intensity of sensation from the rest of the body. CPM works using a loop of signals that ascend into the brain stem and activate the PAG/RVM system. CPM is believed to be another contrast-enhancing process. By itself, CPM has the net effect of increasing the perceived intensity of pain. However, if there is already pain in an area, noxious stimulation in another area will make the intensity of pain from the first area seem less. This is thought to be the reason that “counter-irritation” therapies such as acupuncture, ice, or brisk rubbing outside the area of a wound are effective.
The term "conditioned" in the name of CPM refers to the fact that the sensation is "conditioned" by the counter-stimulation. It does not imply that some form of learning is involved in the process.
A host of studies
demonstrates that the CPM process is less effective than normal in certain groups of pain patients. There is reason to believe that individuals vary in their capacity for or sensitivity to CPM, making some more liable to develop prolonged pain from an acute injury.1