The Gate Control Theory was proposed by Melzack and Wall in 1965 and, with few modifications, remains valid today. It holds that painful impulses, which reach the neurons of the posterior horn, can be blocked by other sensory stimuli, which also reach these neurons, and by nerve impulses coming from the supraspinal nerve centers, which develop a pain modulating activity.
The Gate Control Theory suggests the presence of a mechanism at the level of the central nervous system (CNS) that opens or closes the pain pathways. According to this perspective, the perception of pain is no longer a purely evaluative experience; that is, it incorporates biological as well as psychological aspects.
The Gate Control Theory is based on several principles:
- The transmission of afferent (sensitive) nerve impulses is modulated by a gating system located in the posterior horn of the spinal cord.
- This gating system is influenced by the level of activity of A-B fibers, which are large-diameter nerve fibers that inhibit transmission (close the gate), and A-Delta and C fibers, small diameter fibers that facilitate transmission (open the gate).
- This gating mechanism is also influenced by descending impulses from the cerebral cortex.
- A specialized system of large-diameter, fast transmitting fibers activates specific cognitive processes that influence, via descending fibers, the modulation of the spinal gating mechanism. Thus it is possible that some types of CNS activity may exert control over pain perception.
- When the response of spinal cord transmitting cells exceeds a critical threshold, the activating system, i.e., the neural areas underlying the complex behavioral patterns and characteristic experiences of pain, is activated.
Thus, based on these assumptions, if the transmission impulse is sufficiently inhibited at the medullary level, then the perception of pain, which occurs at the cerebral level, will be blocked.
The development and explanation of the Gate Control Theory remain a subject of debate and research at present.