The gate control theory of pain, put forward by Ron Melzack and Patrick Wall in 1962, is the idea that physical pain is not a direct result of activation of pain receptor neurons, but rather its perception is modulated by interaction between different neurons.
The gate control theory of pain asserts that non-painful input closes the “gates” to painful input, which prevents pain sensation from traveling to the central nervous system. Therefore, stimulation by non-noxious input is able to suppress pain.
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. Combining early concepts derived from the specificity theory and the peripheral pattern theory, the gate control theory is considered to be one of the most influential theories of pain because it provided a neural basis which reconciled the specificity and pattern theories and ultimately revolutionized pain research.
Unlike an actual gate, which opens and closes to allow things to pass through, the “gate” in the spinal cord operates by differentiating between the types of fibers carrying pain signals. Pain signals traveling via small nerve fibers are allowed to pass through, while signals sent by large nerve fibers are blocked. Gate control theory is often used to explain phantom or chronic pain.
The interplay among these connections determines when painful stimuli go to the brain:
- When no input comes in, the inhibitory neuron prevents the projection neuron from sending signals to the brain (gate is closed).
- Normal somatosensory input happens when there is more large-fiber stimulation (or only large-fiber stimulation). Both the inhibitory neuron and the projection neuron are stimulated, but the inhibitory neuron prevents the projection neuron from sending signals to the brain (gate is closed).
- Nociception (pain reception) happens when there is more small-fiber stimulation or only small-fiber stimulation. This inactivates the inhibitory neuron, and the projection neuron sends signals to the brain informing it of pain (gate is open).
Descending pathways from the brain close the gate by inhibiting the projector neurons and diminishing pain perception.
This theory doesn’t tell us everything about pain perception, but it does explain some things. If you rub or shake your hand after you bang your finger, you stimulate normal somatosensory input to the projector neurons. This closes the gate and reduces the perception of pain.