Abstract
The Gate Control Theory of pain, published more than half a century ago to explain nociceptive modulation of peripheral sensory input, assumes inhibition of incoming nociceptive (pain) information produced by mechanical stimulation. To verify the presence of such a gate control mechanism at the level of the human trigeminal system, we evaluated the effects on pain sensation of a proprioceptive trigeminal stimulation induced by mandibular extension. We found that such a stimulation, applied for 7 min, was effective in increasing both the threshold and tolerance of tooth pain induced by electrical activation of dental nociceptors. Moreover the antinociceptive effect lasted for several minutes after the proprioceptive stimulus had ceased. We also tested whether an exteroceptive palatal stimulation superimposed on the proprioceptive stimulation would increase the effects on tooth pain perception of human volunteers. We observed that the exteroceptive stimulation significantly increased the antinociceptive effect induced by the sole proprioceptive stimulation. The physiological mechanisms and the possible implications of these observations are discussed.
Highlights
IntroductionPain originates at the peripheral level and is transported to the central nervous system by sensory fibers (myelinated Aδ and unmyelinated C) called nociceptors
Pain originates at the peripheral level and is transported to the central nervous system by sensory fibers called nociceptors
After one more minute subjects were engaged in one of the following protocols: (1) control group (CTRL), on which no stimulation was applied (n = 112); (2) PROP group, on which a 7 min proprioceptive stimulation performed by imposing a mandibular extension of either 0.5 or 1 cm with the device shown in Figure 1A was applied (n = 128); (3) PROP+EXT group, on which a 7 min proprioceptive stimulation plus an exteroceptive stimulation was applied (n = 56); in this case a device similar to the previous one, but with an additional extension that mechanically stimulates the palate was used (Figure 1B)
Summary
Pain originates at the peripheral level and is transported to the central nervous system by sensory fibers (myelinated Aδ and unmyelinated C) called nociceptors. A major modulatory mechanism is the socalled Gate Control Theory (GCT), hypothesized for the first time by Melzack and Wall (1962). This theory explains the finding that pain originating from a certain body area may be alleviated by tactile, non-nociceptive stimulation of the same region. An example of this modulation is represented by the beneficial effects of a massage on a painful body region. A clear evidence for the Trigeminal Pain Control presence of a trigeminal gate control would surely contribute to new analgesic approaches to treat pain originating from the head and neck
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