{"id":302,"date":"2021-03-22T17:13:20","date_gmt":"2021-03-22T17:13:20","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-hvcc-healthpsychology\/?post_type=chapter&p=302"},"modified":"2021-03-22T17:13:21","modified_gmt":"2021-03-22T17:13:21","slug":"gate-control-theory-of-pain","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-hvcc-healthpsychology\/chapter\/gate-control-theory-of-pain\/","title":{"raw":"Gate control theory of pain","rendered":"Gate control theory of pain"},"content":{"raw":"The\u00a0gate control theory of pain<\/b>, put forward by Ronald Melzack and Patrick Wall in 1962\u00a0[2]<\/a><\/sup>, and again in 1965\u00a0[3]<\/a><\/sup>, is the idea that physical\u00a0pain<\/a>\u00a0is not a direct result of activation of\u00a0pain receptor<\/a>\u00a0neurons<\/a>, but rather its perception is modulated by interaction between different neurons.\r\n\r\n[caption id=\"\" align=\"alignleft\" width=\"257\"]\"\"<\/a> Firing of the\u00a0A\u03b2\u00a0fibers activates the inhibitory interneuron, reducing the chances that the projection neuron will fire, even in the presence of a firing nociceptive fiber.[1][\/caption]\r\n
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\r\n

Development<\/span><\/h2>\r\nExperiments were performed on dogs who were raised confined in cages. When released, the dogs were excited, constantly ran around, and required several attempts to learn to avoid pain. When pain such as a pinch or contact with a burning match was encountered, the animals could not take action to avoid the stimulus immediately. This finding seemed to demonstrate that pain is understood and avoided only by experience--aversion to it is not inbuilt or automatic, and the organism has no way to know what will cause repeated pain without a repeated experience....\r\n

Physiology<\/span><\/h2>\r\nAfferent<\/a>\u00a0pain-receptive nerves, those that bring signals to the brain, comprise at least two kinds of fibers - a fast, relatively thick,\u00a0myelinated<\/a>\u00a0\"A\u03b4\" fiber<\/a>\u00a0that carries messages quickly with intense pain, and a small, unmyelinated, slow\u00a0\"C\" fiber<\/a>\u00a0that carries the longer-term throbbing and\u00a0chronic pain<\/a>. Large-diameter A\u03b2 fibers are nonnociceptive (do not transmit pain stimuli) and inhibit the effects of firing by A\u03b4 and C fibers.\r\n\r\nThe\u00a0peripheral nervous system<\/a>\u00a0has centers at which pain stimuli can be regulated. Some areas in the\u00a0dorsal horn<\/a>\u00a0of the\u00a0spinal cord<\/a>\u00a0that are involved in receiving pain stimuli from A\u03b4 and C fibers, called laminae, also receive input from A\u03b2 fibers (Kandel et al., 2000). The nonnociceptive fibers indirectly inhibit the effects of the pain fibers, 'closing a gate' to the transmission of their stimuli (Kandel et al., 2000). In other parts of the laminae, pain fibers also inhibit the effects of nonnociceptive fibers, 'opening the gate'.\r\n\r\nAn inhibitory connection may exist with A\u03b2 and C fibers, which may form a\u00a0synapse<\/a>\u00a0on the same projection neuron. The same neurons may also form synapses with an inhibitory interneuron that also synapses on the projection neuron, reducing the chance that the latter will fire and transmit pain stimuli to the\u00a0brain<\/a>. The C fiber's synapse would inhibit the inhibitory interneuron, indirectly increasing the projection neuron's chance of firing. The A\u03b2 fiber, on the otherhand, forms an\u00a0excitatory<\/i>\u00a0connection with the inhibitory interneuron, thus\u00a0decreasing<\/i>\u00a0the projection neuron's chance of firing (like the C fiber, the A\u03b2 fiber also has an excitatory connection on the projection neuron itself). Thus, depending on the relative rates of firing of C and A\u03b2 fibers, the firing of the nonnociceptive fiber may inhibit the firing of the projection neuron and the transmission of pain stimuli (Kandel et al., 2000).\r\n\r\nGate control theory thus explains how stimulus that activates only nonnociceptive nerves can inhibit pain. The pain seems to be lessened when the area is rubbed because activation of nonnociceptive fibers inhibits the firing of nociceptive ones in the laminae (Kandel et al., 2000). In transcutaneous electrical stimulation (TENS), nonnociceptive fibers are selectively stimulated with\u00a0electrodes<\/a>\u00a0in order to produce this effect and thereby lessen pain.\r\n\r\nOne area of the brain involved in reduction of pain sensation is the periaqueductal gray matter that surrounds the\u00a0third ventricle<\/a>\u00a0and the\u00a0cerebral aqueduct<\/a>\u00a0of the\u00a0ventricular system<\/a>. Stimulation of this area produces\u00a0analgesia<\/a>\u00a0(but not total numbing) by activating descending pathways that directly and indirectly inhibit nociceptors in the laminae of the spinal cord (Kandel et al., 2000). It also activates\u00a0opioid<\/a>\u00a0receptor-containing parts of the spinal cord.\r\n\r\nAfferent 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 point out that\u00a0pain is in the brain<\/b>.\r\n

Advantages of the theory<\/span><\/h2>\r\nThe brain in prior theories of\u00a0neurochemistry<\/a>\u00a0had simply not been taken into account - pain was thought to be simply a direct response to a stimulus - the so-called pain-pleasure theory, a one-way \"alarm system\" like that proposed by\u00a0Ren\u00e9 Descartes<\/a>. This did not, for instance, explain why a carpenter can hit his thumb and not feel much pain, whereas a novice is doubled over in agony, nor did it explain\u00a0phantom limb pain<\/a>, when the signal is in fact impossible to receive, since the wiring for it is\u00a0gone<\/i>.\r\n

Consequences<\/span><\/h2>\r\nIn his paper\u00a0The Tragedy of Needless Pain<\/i>, Melzack further asserts that pain is a fundamental human experience, and requires an integrative understanding of that whole experience, and every choice we have made, that has formed our own \"gates\". He frames the choice to deal with pain or ignore it as moral: if the brain\u00a0can<\/i>\u00a0control pain, we who know that\u00a0must<\/i>\u00a0make use of that capacity, and in turn take control of pain on a species level - only by doing so can we achieve control of the larger causes of all of the pain that humans cause each other by carelessness, hatred, and failures of\u00a0empathy<\/a>\u00a0- which might extend beyond humans.\r\n\r\nThe impact of this theory on medical treatment for pain has been profound, and has made it a multi-disciplinary field. A major advantage of the theory is that those being taught pain control techniques can actually be told\u00a0why<\/i>\u00a0they work. This seems to play a major role in achieving results - which is explained most readily by\u00a0psychoneuroimmunology<\/a>, in which the nerves are seen as the link between the\u00a0immune system<\/a>\u00a0and sensory and cognitive experience.\r\n\r\nLearning to control chronic benign pain usually takes about ten classes at the\u00a0McGill University<\/a>\u00a0pain control centre founded by Melzack. The classes cover areas such as\u00a0diet<\/a>\u00a0(tryptophan<\/a>-heavy foods such as turkey help control pain),\u00a0drugs<\/a>,\u00a0psychiatry<\/a>,\u00a0social network<\/a>\u00a0choices. Very often, chronic pain restricts sufferers' choices of friends, activities, lifestyle and profession, making them feel as though they are not in control of their lives. In the gate control theory, this is only to be expected, as the failure to control pain can be seen as a\u00a0mental illness<\/a>\u00a0- a brain being unable to deal with challenges that a body faces.\r\n\r\nPain being an entirely personal experience, it is difficult to measure, but Melzack's\u00a0McGill Pain Questionnaire<\/i>\u00a0asks a number of directed questions to assess and categorize that experience. By collecting words used to describe pain by the patients themselves, Melzack ended up with about 200 words. A \"burning pain\" for instance, can be described as \"hot\" or even \"searing\". \"Throbbing\" becomes \"palpitating\". Some describe sensory aspects of pain, and others, such as \"excruciating\", describe emotional experiences. More intense pain generally requires more words to describe. A patient, in the questionnaire, picks one of 20 set of words to describe their pain, and assign it a point on a scale. The test is used all over the world, but culture and language seem not to matter - the same words appear in almost every assessment in different languages. For instance, group 1 lays out the scale \"flickering, quivering, pulsing, throbbing,\" all of which imply some kind of movement or change. Another group has the words \"hot, burning, scalding, searing\". These words seem to describe actual experiences, something common to the hominid nervous system.\r\n\r\nIn\u00a0The Body in Pain<\/i>, Elaine Scarry writes that this process was the first to actually qualify and define\u00a0types of pain<\/b>\u00a0- something impossible prior to the gate control theory. An advantage of this was to make it easier to determine the difference between\u00a0organic pain<\/b>\u00a0and\u00a0non-organic pain<\/b>\u00a0- the latter being entirely treatable by psychological means.\r\n\r\nHealing<\/a>\u00a0is directly affected by the physiological way the body behaves when the brain is or is not experiencing pain -\u00a0post-traumatic stress disorder<\/a>\u00a0for instance can set in a long time after the physical insult, causing inordinate levels of caution, emotional withdrawal, and dealing an injury not just to the body but to the whole person. Rates of healing are drastically affected - more serious injuries can be recovered from up to three times more quickly when pain is under control, than when it is not.\r\n\r\nThe\u00a0phantom limb<\/a>\u00a0pain commonly experienced even by\u00a0quadriplegics<\/a>\u00a0who have lost large portions of the\u00a0spinal cord<\/a>\u00a0and cannot possibly be receiving any messages from it, is explained most readily by Melzack's notion of the\u00a0body-self neuro-matrix<\/b>, a sort of committee that can create a composite map of the body, and \"represents the sense of self of the body\". The sensation of a foot that is burning, for instance, has become separated from the foot that is still attached to a useless leg dangling into space - the disconnection actually frees the neurological part of the matrix to \"invent\" a body. Different parts of the brain then perceive the whole body in different ways, and these are more free to clash if real signals from a real body are not disciplining them all with a common external experience.\r\n

Corroboration<\/span><\/h2>\r\nThis theory is corroborated by Reynold's comparative study on rats. By stimulating a certain area of the brain (the periaque-ductal area in the midbrain), Reynolds could induce\u00a0analgesia<\/a>\u00a0to such an extent that the animal subjects of the experiment could undergo painless abdominal surgery whilst awake. This ties in with the Gate Control Theory, which posits that brain activity can affect the level of pain experienced.\r\n\r\n<\/div>\r\n<\/sup><\/div>","rendered":"

The\u00a0gate control theory of pain<\/b>, put forward by Ronald Melzack and Patrick Wall in 1962\u00a0[2]<\/a><\/sup>, and again in 1965\u00a0[3]<\/a><\/sup>, is the idea that physical\u00a0pain<\/a>\u00a0is not a direct result of activation of\u00a0pain receptor<\/a>\u00a0neurons<\/a>, but rather its perception is modulated by interaction between different neurons.<\/p>\n

\"\"<\/a><\/p>\n

Firing of the\u00a0A\u03b2\u00a0fibers activates the inhibitory interneuron, reducing the chances that the projection neuron will fire, even in the presence of a firing nociceptive fiber.[1]<\/p>\n<\/div>\n

\n
\n

Development<\/span><\/h2>\n

Experiments were performed on dogs who were raised confined in cages. When released, the dogs were excited, constantly ran around, and required several attempts to learn to avoid pain. When pain such as a pinch or contact with a burning match was encountered, the animals could not take action to avoid the stimulus immediately. This finding seemed to demonstrate that pain is understood and avoided only by experience–aversion to it is not inbuilt or automatic, and the organism has no way to know what will cause repeated pain without a repeated experience….<\/p>\n

Physiology<\/span><\/h2>\n

Afferent<\/a>\u00a0pain-receptive nerves, those that bring signals to the brain, comprise at least two kinds of fibers – a fast, relatively thick,\u00a0myelinated<\/a>\u00a0“A\u03b4” fiber<\/a>\u00a0that carries messages quickly with intense pain, and a small, unmyelinated, slow\u00a0“C” fiber<\/a>\u00a0that carries the longer-term throbbing and\u00a0chronic pain<\/a>. Large-diameter A\u03b2 fibers are nonnociceptive (do not transmit pain stimuli) and inhibit the effects of firing by A\u03b4 and C fibers.<\/p>\n

The\u00a0peripheral nervous system<\/a>\u00a0has centers at which pain stimuli can be regulated. Some areas in the\u00a0dorsal horn<\/a>\u00a0of the\u00a0spinal cord<\/a>\u00a0that are involved in receiving pain stimuli from A\u03b4 and C fibers, called laminae, also receive input from A\u03b2 fibers (Kandel et al., 2000). The nonnociceptive fibers indirectly inhibit the effects of the pain fibers, ‘closing a gate’ to the transmission of their stimuli (Kandel et al., 2000). In other parts of the laminae, pain fibers also inhibit the effects of nonnociceptive fibers, ‘opening the gate’.<\/p>\n

An inhibitory connection may exist with A\u03b2 and C fibers, which may form a\u00a0synapse<\/a>\u00a0on the same projection neuron. The same neurons may also form synapses with an inhibitory interneuron that also synapses on the projection neuron, reducing the chance that the latter will fire and transmit pain stimuli to the\u00a0brain<\/a>. The C fiber’s synapse would inhibit the inhibitory interneuron, indirectly increasing the projection neuron’s chance of firing. The A\u03b2 fiber, on the otherhand, forms an\u00a0excitatory<\/i>\u00a0connection with the inhibitory interneuron, thus\u00a0decreasing<\/i>\u00a0the projection neuron’s chance of firing (like the C fiber, the A\u03b2 fiber also has an excitatory connection on the projection neuron itself). Thus, depending on the relative rates of firing of C and A\u03b2 fibers, the firing of the nonnociceptive fiber may inhibit the firing of the projection neuron and the transmission of pain stimuli (Kandel et al., 2000).<\/p>\n

Gate control theory thus explains how stimulus that activates only nonnociceptive nerves can inhibit pain. The pain seems to be lessened when the area is rubbed because activation of nonnociceptive fibers inhibits the firing of nociceptive ones in the laminae (Kandel et al., 2000). In transcutaneous electrical stimulation (TENS), nonnociceptive fibers are selectively stimulated with\u00a0electrodes<\/a>\u00a0in order to produce this effect and thereby lessen pain.<\/p>\n

One area of the brain involved in reduction of pain sensation is the periaqueductal gray matter that surrounds the\u00a0third ventricle<\/a>\u00a0and the\u00a0cerebral aqueduct<\/a>\u00a0of the\u00a0ventricular system<\/a>. Stimulation of this area produces\u00a0analgesia<\/a>\u00a0(but not total numbing) by activating descending pathways that directly and indirectly inhibit nociceptors in the laminae of the spinal cord (Kandel et al., 2000). It also activates\u00a0opioid<\/a>\u00a0receptor-containing parts of the spinal cord.<\/p>\n

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 point out that\u00a0pain is in the brain<\/b>.<\/p>\n

Advantages of the theory<\/span><\/h2>\n

The brain in prior theories of\u00a0neurochemistry<\/a>\u00a0had simply not been taken into account – pain was thought to be simply a direct response to a stimulus – the so-called pain-pleasure theory, a one-way “alarm system” like that proposed by\u00a0Ren\u00e9 Descartes<\/a>. This did not, for instance, explain why a carpenter can hit his thumb and not feel much pain, whereas a novice is doubled over in agony, nor did it explain\u00a0phantom limb pain<\/a>, when the signal is in fact impossible to receive, since the wiring for it is\u00a0gone<\/i>.<\/p>\n

Consequences<\/span><\/h2>\n

In his paper\u00a0The Tragedy of Needless Pain<\/i>, Melzack further asserts that pain is a fundamental human experience, and requires an integrative understanding of that whole experience, and every choice we have made, that has formed our own “gates”. He frames the choice to deal with pain or ignore it as moral: if the brain\u00a0can<\/i>\u00a0control pain, we who know that\u00a0must<\/i>\u00a0make use of that capacity, and in turn take control of pain on a species level – only by doing so can we achieve control of the larger causes of all of the pain that humans cause each other by carelessness, hatred, and failures of\u00a0empathy<\/a>\u00a0– which might extend beyond humans.<\/p>\n

The impact of this theory on medical treatment for pain has been profound, and has made it a multi-disciplinary field. A major advantage of the theory is that those being taught pain control techniques can actually be told\u00a0why<\/i>\u00a0they work. This seems to play a major role in achieving results – which is explained most readily by\u00a0psychoneuroimmunology<\/a>, in which the nerves are seen as the link between the\u00a0immune system<\/a>\u00a0and sensory and cognitive experience.<\/p>\n

Learning to control chronic benign pain usually takes about ten classes at the\u00a0McGill University<\/a>\u00a0pain control centre founded by Melzack. The classes cover areas such as\u00a0diet<\/a>\u00a0(tryptophan<\/a>-heavy foods such as turkey help control pain),\u00a0drugs<\/a>,\u00a0psychiatry<\/a>,\u00a0social network<\/a>\u00a0choices. Very often, chronic pain restricts sufferers’ choices of friends, activities, lifestyle and profession, making them feel as though they are not in control of their lives. In the gate control theory, this is only to be expected, as the failure to control pain can be seen as a\u00a0mental illness<\/a>\u00a0– a brain being unable to deal with challenges that a body faces.<\/p>\n

Pain being an entirely personal experience, it is difficult to measure, but Melzack’s\u00a0McGill Pain Questionnaire<\/i>\u00a0asks a number of directed questions to assess and categorize that experience. By collecting words used to describe pain by the patients themselves, Melzack ended up with about 200 words. A “burning pain” for instance, can be described as “hot” or even “searing”. “Throbbing” becomes “palpitating”. Some describe sensory aspects of pain, and others, such as “excruciating”, describe emotional experiences. More intense pain generally requires more words to describe. A patient, in the questionnaire, picks one of 20 set of words to describe their pain, and assign it a point on a scale. The test is used all over the world, but culture and language seem not to matter – the same words appear in almost every assessment in different languages. For instance, group 1 lays out the scale “flickering, quivering, pulsing, throbbing,” all of which imply some kind of movement or change. Another group has the words “hot, burning, scalding, searing”. These words seem to describe actual experiences, something common to the hominid nervous system.<\/p>\n

In\u00a0The Body in Pain<\/i>, Elaine Scarry writes that this process was the first to actually qualify and define\u00a0types of pain<\/b>\u00a0– something impossible prior to the gate control theory. An advantage of this was to make it easier to determine the difference between\u00a0organic pain<\/b>\u00a0and\u00a0non-organic pain<\/b>\u00a0– the latter being entirely treatable by psychological means.<\/p>\n

Healing<\/a>\u00a0is directly affected by the physiological way the body behaves when the brain is or is not experiencing pain –\u00a0post-traumatic stress disorder<\/a>\u00a0for instance can set in a long time after the physical insult, causing inordinate levels of caution, emotional withdrawal, and dealing an injury not just to the body but to the whole person. Rates of healing are drastically affected – more serious injuries can be recovered from up to three times more quickly when pain is under control, than when it is not.<\/p>\n

The\u00a0phantom limb<\/a>\u00a0pain commonly experienced even by\u00a0quadriplegics<\/a>\u00a0who have lost large portions of the\u00a0spinal cord<\/a>\u00a0and cannot possibly be receiving any messages from it, is explained most readily by Melzack’s notion of the\u00a0body-self neuro-matrix<\/b>, a sort of committee that can create a composite map of the body, and “represents the sense of self of the body”. The sensation of a foot that is burning, for instance, has become separated from the foot that is still attached to a useless leg dangling into space – the disconnection actually frees the neurological part of the matrix to “invent” a body. Different parts of the brain then perceive the whole body in different ways, and these are more free to clash if real signals from a real body are not disciplining them all with a common external experience.<\/p>\n

Corroboration<\/span><\/h2>\n

This theory is corroborated by Reynold’s comparative study on rats. By stimulating a certain area of the brain (the periaque-ductal area in the midbrain), Reynolds could induce\u00a0analgesia<\/a>\u00a0to such an extent that the animal subjects of the experiment could undergo painless abdominal surgery whilst awake. This ties in with the Gate Control Theory, which posits that brain activity can affect the level of pain experienced.<\/p>\n<\/div>\n

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Candela Citations<\/h3>\n\t\t\t\t\t
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Public domain content<\/div>