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Last updated: Sun, Mar 9, 2025
The gate-control theory is significant because it was the first major successful alternative to theories based on specificity. We now know that the mechanisms of gate control are only a small part of the complexity of pain perception. This section describes some extensions and refinements made in the years following the 60s.
The gate-control theory predicts that innocuous stimulation from large fibers can inhibit painful sensation. When Wall and another researcher tested this prediction with human subjects, they applied electrical stimulation at levels that would trigger innocuous low-threshold signals. The procedure reduced pain. TENS (transcutaneous electrical nerve stimulation) was developed directly out of this finding.1
Cells have been found in the RVM that are involved in descending modulation of pain. One group, called OFF-cells, causes reduced pain when activated. OFF-cells are activated by opioids and are required for opioid analgesia. ON-cells facilitate perception of pain. Both classes project down to layers I, II, and V in the spinal dorsal horn. ON-cells seem to be activated as a group, therefore they have a general sensitizing effect throughout the body. OFF-cells also seem to become activated as a group. Experiments with rats (which are often used as a model for humans) show that when the ON-cells are activated, the animal becomes more sensitive to innocuous stimuli, including light touch and even sound.
Some of the sophistication and complexity of the pain-regulation systems is demonstrated by an experiment from the early 1980s. Experimenters monitored the action of spinal cells while and after they trained a monkey to play a game. The monkey's task was to hit a switch when a thermal stimulus attached to its skin was turned on. The monkey received food as a reward. Before the monkey had learned to play the game, the spinal cells, as expected, would simply activate when the thermal stimulus was turned on. After the monkey had learned the game, the cells would activate once when the signal to start the game was given, and then again when the thermal stimulus was turned on.2
Other research revealed that descending inhibition in the deeper laminae of the dorsal horn is selective—input from small-diameter fibers can be suppressed while innocuous input on the larger fibers isn't.
Despite our extensive knowledge of the circuit properties and pharmacological responsiveness of descending modulatory networks, knowledge of their physiological function and clinical significance is tentative. Adding to the complexity of this analysis, several pain-modulating networks are operating in parallel, and understanding the net behavioral effect of their combined actions requires parsing the contribution of each under a variety of conditions.3
See The Descending Tracts and Descending Pain Modulation for a more complete modern view of descending pain modulation.