Gate control theory of pain
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 that reconciled the specificity and pattern theories and ultimately revolutionized pain research.
Although there are some important observations which the gate control theory cannot explain adequately, it remains the only theory of pain that most accurately accounts for the physical and psychological aspects of pain perception.
Willem Noordenbos (1910–1990), a Dutch researcher at the University of Amsterdam, was the first one to propose a model with an interaction between small (unmyelinated) and thick (myelinated) fibers in 1959. The fast (myelinated) fibers block the slow (unmyelinated) fibers, "fast blocks slow".
Proposed mechanisms
When you experience a negative feeling, such as pain from a bump or an itch from a bug bite, a common reaction is an attempt to eliminate the feeling by rubbing the painful bump or scratching the itchy bite. Gate control theory asserts that activation of nerves that do not transmit pain signals, called non-nociceptive fibers, can interfere with signals from pain fibers, thereby inhibiting pain. 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. Transmission Cells that carry the pain signal up to the brain, and
- 2. Inhibitory Interneurons that impede transmission cell activity. Activation of transmission cells occurs from both excitatory small-diameter and excitatory large-diameter fibers.
However, activation of the inhibitory interneurons varies: large-diameter fibers excite the interneuron, which ultimately reduces transmission cell firing, whereas small-diameter fibers inhibit the inhibitory interneuron which lessens the inhibitory input to the transmission cell. Therefore, less pain is felt (via reduced transmission cell activity) when more activity in large-diameter fibers (touch-, pressure-, and vibration- transmitting) occurs relative to the activity in small-diameter (pain-transmitting) fibers.
Therapeutic uses
The mechanism of gate control theory can be used therapeutically. Gate control theory thus explains how stimulus that activates only non-nociceptive nerves can inhibit pain. The pain seems to be lessened when the area is rubbed because activation of non-nociceptive fibers inhibits the firing of nociceptive ones in the laminae. In transcutaneous electrical nerve stimulation (TENS), non-nociceptive fibers are selectively stimulated with electrodes in order to produce this effect and thereby lessen pain.
One area of the brain involved in the 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. Descending pathways also activate opioid receptor-containing parts of the spinal cord.
Afferent pathways interfere with each other constructively, so that the brain can control the degree of pain that is perceived, based on which pain stimuli are to be ignored to pursue potential gains. The brain determines which stimuli are profitable to ignore over time. Thus, the brain controls the perception of pain quite directly and can be "trained" to turn off forms of pain that are not "useful". This understanding led Melzack to assert that pain is in the brain.
Gate control theory influenced the development of mindfulness-based pain management (MBPM).
- More information is available at [ Wikipedia:Gate_control_theory_of_pain ]
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