Consequences of the Gate-Control Theory

What Drs. Melzack and Wall did with their gate-control theory was open up new ways of looking at pain; they also opened up new ways of treating pain. From the idea of modulating the pain signal, Dr. Wall developed transcutaneous electrical nerve stimulation, or TENS . What TENS does is bombard the peripheral afferent nerve endings with electrical stimuli, which seems to change the input going into the dorsal horn of the spinal cord, so that it actually ends up 'closing the gate' and turning off the pain.

A good example of a population for whom such discoveries have made a marked difference are people with fibromyalgia, who certainly know a thing or two about chronic pain — and the deep frustration of other people's misunderstanding. 'There are no visible signs of fibromyalgia,' says rheumatologist Dr. Glenn McCain, a fibromyalgia specialist formerly at the University Hospital in London, Ont., now director of a fibromyalgia treatment program in Charlotte, N.C., 'except for the fact that you're complaining of it. You may walk with a limp or you may not move as quickly as a healthy person, but generally speaking nobody could tell there's anything wrong with you.'

Fibromyalgia patients characteristically complain of generalized chronic muscular pain, along with fatigue. But the hallmark physical finding, says McCain, 'is the presence of fibrositic tender points in specific anatomical locations that don't vary from patient to patient. There's something very important about these points, but we don't yet understand it.'

What makes it even worse is that, many people with fibromyalgia also have rheumatoid arthritis or lupus. Investigators are really only beginning to understand the syndrome, but there are a number of theories. One, not surprisingly, concerns the way people experience pain. 'Just the circuitry of how pain impulses are transmitted through the body is very complex,' says McCain. 'But one theory is that fibromyalgia is simply disregulation of the normal pain pathway.'

The point is that there are occasional overlaps in the body circuitry; the same nerves that supply the diaphragm, for example, also supply sensation to the tip of the shoulder. If there's pain in one area, it can sometimes be experienced in the other; it's called referred pain. Scientists know very little of how a pain impulse gets to the brain and is modulated, or transformed into a recognizable sensation, but the gate-control theory of pain modulation has opened up the idea that the experience of pain is the result of a complex of different neuronal interactions, each triggered by different chemical neurotransmitters — or maybe the same neurotransmitters.

In that sense, the nervous system has the complexity of the immune system. If you have an abnormal regulation of certain cells in the immune system, you end up with an autoimmune disease, such as rheumatoid arthritis or lupus. It could be a similar phenomenon with pain: If there's some kind of abnormal regulation of the neuronal networks, that could lead to a more severe experience of pain. At least, that's one theory. Dr. Melzack readily admits that the gate-control theory only went so far. They didn't try to find out what happens beyond the gate — an omission they've since begun to rectify by studying the two sets of 'pathways' that convey information up to the brain. Rapidly conducting pathways tell the brain where an injury has occurred and how severe it is; the brain can then make adjustments to account for it, as in reflexes that draw an injured extremity away from the source of the injury — the finger from the flame.

Slowly conducting systems, on the other hand, give rise to affect and emotion: They're the ones involved in most forms of chronic pain, including the pain of arthritic — continual input travelling the slowly conducting pathways. The pain is poorly localized; in other words, you may feel your arthritis pain somewhere in the region of your knee or shoulder, but you don't locate it as precisely as stepping on a tack or burning your finger.

'Fast' pain, or phasic pain, carries a great deal of what's known as sensory-discriminative information, which can be described with words like pulsing, pounding, beating, throbbing, or hot, burning, searing. These are sensory qualities of pain. The other dimension — the emotional or affective dimension of pain — is the constant, slowly conducted ache of chronic pain. It's the pain, says Dr. Melzak, 'that drives you crazy, that makes you get into bed or call the doctor or take pills or jump off a bridge. This is what persists to make you utterly miserable, and that's the affective component of pain.'

This page was last reviewed/updated on : 02/23/2008