By the 1950s, the specificity theory had been strongly supported by the work of Joseph Erlanger, Herbert Gasser, and Ainsley Iggo, who had recorded pain impulses from single nerve fibers. But several investigators proposed alternative physiological models to replace the specific one-to-one pain pathway of perception and response, which might better explain the clinical observations of Beecher, Leriche, Livingston, and others. These included the pattern theory of Graham Weddell and D.C. Sinclair, which suggested that pain perception was the interpretation of the spatial and temporal patterns of stimuli, and the multisynaptic modification system proposed by the Dutch surgeon Willem Noordenbos. However, these theories lacked strong experimental support.
"One-one synaptic transmission must be the exception rather than the rule in the nervous system. Any nerve cell located in the anterior horn. . . could hardly be expected to synapse at higher level with one such similar cell only. It will probably send ramifications to many other locations, and in turn be acted upon by the ramifications of many other cells. . . Far from being a continuous chain of short neurons, these fibres must constitute links in an extremely complicated nerve net in which, within limits, everything synapses more or less with everything else."
Diagrammatic representation of the Multisynaptic Afferent System by Willem Noordenbos (Pain:
Problems Pertaining to the Transmission of Nerve Impulses Which Give Rise to Pain.
Amsterdam: Elsevier, 1959)(not reproduced pending permission to use)
In 1965, a collaboration between two self-described iconoclasts, Canadian psychologist Ronald Melzack and British physiologist Patrick Wall, produced the gate control theory. Their paper, "Pain Mechanisms: a New Theory," (Science: 150, 171-179, 1965) has been described as "the most influential ever written in the field of pain." Melzack and Wall suggested a gating mechanism within the spinal cord that closed in response to normal stimulation of the fast conducting "touch" nerve fibers; but opened when the slow conducting "pain" fibers transmitted a high volume and intensity of sensory signals. The gate could be closed again if these signals were countered by renewed stimulation of the large fibers.
Melzack and Wall remember their collaboration on the Gate Control paper:
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| | Ronald Melzack | |
Melzack: "So in the course of our talking I said to Pat, 'You know, you and I think a lot alike about a lot of things. Why don't we write a paper together?' So we wrote a paper that was published in Brain in 1962. And we struggled with that paper, putting it all together, and it was certainly jointly done all the way through. I think three people read the paper. So we began to write [a second] paper and sending back drafts back and forth-I'd bring them down, we would argue, and so on-and then at some stage, we began to organize the paper into components, and the main, the gate control theory got invented. Anyway, I suggested that we really aim for the top and try Science and see what the hell happens-the worst that will happen is to get rejected. It got accepted. We were astounded. Well, so, then you know the rest because some people loved it and most people hated it." (From the Oral History of Ronald Melzack, 1993.)
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| | Patrick D. Wall | | Sketch of the gate, c.1965 | |
Wall: "At this time, with a completely different background, there was Ron Melzack, with whom I've really never worked in my life, we'd only got to talking. You ask about the gate control theory, which is 1965 as published, if you read what we'd published certainly three years before, it says exactly the same thing in it. And we tossed a coin, and published essentially exactly the same paper, only as Wall and Melzack [1962] rather than Melzack and Wall [1965], and it was utterly ignored. And then we put out the Science paper. And as you see, if you read this, we simply tried to bring together everything that we knew and what was in the literature at the time, knowing very well that we could be wrong, and certainly in the details." (From the Oral History of Patrick D. Wall, 1993.)
In Pain Mechanisms: a New Theory, Melzack and Wall traced the history of the specific pain pathway back to the 16th century philosopher René Descartes's idea of "pulling on a thread."
In this schematic, Melzack shows the evolution of physiological pain models: the specific pathway; Livingston's vicious circle; Noordenbos' multisynaptic system; and the gate control model.
Gate control offered a new heuristic for pain research, one which integrated experimental and clinical observations, and inspired many young scientists to begin work on the problem. Although the model has been much revised since 1965, the idea of the modulation of pain perception within the nervous system continues to be central to pain studies.
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