Gate control theory

A painful, nociceptive stimulus stimulates primary afferent fibers and travels to the brain via transmission cells.

First proposed in 1965 by Ronald Melzack and Patrick Wall, the theory offers a physiological explanation for the previously observed effect of psychology on pain perception.

[2] Willem Noordenbos (1910–1990), a Dutch researcher at the University of Amsterdam, proposed in 1959 a model which featured interaction between small (unmyelinated) and thick (myelinated) fibers.

[citation needed] It is proposed that both small-diameter (pain-transmitting) and large-diameter (touch-, pressure-, and vibration- transmitting) afferent nerve fibers carry information from the site of the injury to two destinations in the dorsal horn: 1.

[4] The C fiber's synapse would inhibit the inhibitory interneuron, indirectly increasing the projection neuron's chance of firing.

[8] The authors proposed that both thin (pain) and large diameter (touch, pressure, vibration) nerve fibers carry information from the site of injury to two destinations in the spinal cord: transmission cells that carry the pain signal up to the brain, and inhibitory interneurons that impede transmission cell activity.

[9] They pictured not only a signal traveling from the site of injury to the inhibitory and transmission cells and up the spinal cord to the brain, but also a signal traveling from the site of injury directly up the cord to the brain (bypassing the inhibitory and transmission cells) where, depending on the state of the brain, it may trigger a signal back down the spinal cord to modulate inhibitory cell activity (and so pain intensity).

The theory offered a physiological explanation for the previously observed effect of psychology on pain perception.

[10] In 1968, three years after the introduction of the gate control theory, Ronald Melzack concluded that pain is a multidimensional complex with numerous sensory, affective, cognitive, and evaluative components.

The pain seems to be lessened when the area is rubbed because activation of nonnociceptive fibers inhibits the firing of nociceptive ones in the laminae.

[4] One area of the brain involved in reduction of pain sensation is the periaqueductal gray matter that surrounds the third ventricle and the cerebral aqueduct of the ventricular system.

Stimulation of this area produces analgesia (but not total numbing) by activating descending pathways that directly and indirectly inhibit nociceptors in the laminae of the spinal cord.

[citation needed] Gate control theory influenced the development of mindfulness-based pain management (MBPM).

In the top panel, the nonnociceptive, large-diameter sensory fiber (orange) is more active than the nociceptive small-diameter fiber (blue), therefore the net input to the inhibitory interneuron (red) is net positive. The inhibitory interneuron provides presynaptic inhibition to both the nociceptive and nonnociceptive neurons, reducing the excitation of the transmission cells. In the bottom panel, an open "gate" (free-flowing information from afferents to the transmission cells) is pictured. This occurs when there is more activity in the nociceptive small-diameter fibers (blue) than the nonnociceptive large-diameter fibers (orange). In this situation, the inhibitory interneuron is silenced, which relieves inhibition of the transmission cells. This "open gate" allows for transmission cells to be excited, and thus pain to be sensed.
The firing of the projection neuron determines pain. The inhibitory interneuron decreases the chances that the projection neuron will fire. Firing of C fibers inhibits the inhibitory interneuron (indirectly), increasing the chances that the projection neuron will fire. [ 4 ] Inhibition is represented in blue, and excitation in yellow. A lightning bolt signifies increased neuron activation, while a crossed-out bolt signifies weakened or reduced activation.
Firing of the Aβ fibers activates the inhibitory interneuron, reducing the chances that the projection neuron will fire, even in the presence of a firing nociceptive fiber. [ 4 ]