Gate Control Theory of Pain

The gate control theory of pain says pain is not a simple message sent from an injury to the brain. A gate in the spinal cord decides how much of the signal gets through. Touch can close the gate, damage signals can open it, and the brain can adjust it. Melzack and Wall proposed it in 1965.

How Does the Gate Control Theory Explain Pain?

An Example: Why Rubbing a Bump Helps

Hit your shin on a table and it hurts. Rub it, and the pain eases. The gate theory can explain effects like this.

Two kinds of nerve fibre take part. Small fibres carry much of the damage signal, and large fibres carry touch.

In the model, some spinal cells, called gate cells, keep the gate shut while they are active. When they go quiet, the gate opens. The steps below follow Mendell’s (2014) review of the theory.

1. The bump: Small fibres at the injury fire hard, sending a burst of signals. They silence the gate cells, so the gate opens.
2. The open gate: The damage signal passes through to other spinal cells that relay it to the brain. You feel pain.
3. The rub: Rubbing fires large fibres that carry touch. They switch the gate cells back on, so the gate shuts.
4. The closing gate: Less signal reaches the brain, so the pain eases.

The brain can join in. Worry about the injury can send signals down that open the gate again. A gripping conversation can help to close it.

This is a plausible use of the theory, not a controlled demonstration. Rubbing also distracts you and raises your hope of relief.

The testable prediction is narrower. Adding touch signals on their own should reduce the pain that small fibres carry.

The Two Kinds of Nerve Fibre

Nerve fibres are the long, thin cables that carry signals from the body to the spinal cord. The theory depends on two kinds. Both are part of the sensory neurons that report on the body.

• Large fibres (A-beta): They mainly carry touch and pressure. An insulating coating called myelin makes their signals fast.
• Small fibres (A-delta and C): They carry much of the damage signal. A-delta fibres have a thin coating. C fibres have none.

Receptors that respond to harmful stimuli are called nociceptors. Most of them use small fibres.

In the 1965 model, both kinds of fibre feed the same cells in the spinal cord. What differs is how each kind affects the gate.

The Gate in the Spinal Cord

The spinal cord and the brain together make up the central nervous system.

The dorsal horn is the part of the spinal cord where sensory fibres from the body first connect to spinal cells. The gate is thought to operate there.

The gate controls how much signal reaches the transmission (T) cells. They receive both kinds of input and send the result on to the brain.

Wall proposed that cells in the substantia gelatinosa, a dense layer at the surface of the dorsal horn, control the flow of signals (Mendell, 2014). These are the gate cells.

In the model, large-fibre activity switches on the gate cells. They then block signals from reaching the transmission cells, so the gate closes.

Small-fibre activity does the opposite. It silences the gate cells. That lifts the block, so the gate opens (Mendell, 2014).

In the model, you feel pain only when the transmission cells’ output passes a critical level (Mendell, 2014).

In the model, a painful stimulus that lasts tends to open the gate. Large fibres adapt, so their signal fades, while small fibres keep firing (Mendell, 2014).

Central Control: The Brain Adjusts the Gate

The model also gave the brain a job. In the theory, central control means that signals from the brain can travel back down and open or close the gate.

Melzack (1999) later judged this the theory’s most important contribution. It forced science to accept the brain as an active system that filters, selects and changes incoming signals.

The next section looks at how the brain does this.

How Does the Brain Control the Gate?

The theory included the idea that the brain can turn pain down.

It predicted that the brain could reach down and regulate signals in the spinal cord. The pathways the brain uses to do this are called the descending pain-control system.

Experiments in animals soon supported the idea.

Stimulating the Brain Blocks Pain in Animals

Reynolds (1969) asked whether stimulating one brain region could block pain well enough for surgery.

Reynolds implanted electrodes in the midbrain of eight rats. In three of them, stimulation removed responses to painful stimuli while other movement stayed normal.

Surgery on the abdomen was then carried out during stimulation, without chemical anaesthetic. Responses to painful stimuli returned when the stimulation stopped.

The best electrode sites lay at the edge of the central grey, a region of the midbrain. The midbrain is part of the brainstem, which links the brain to the spinal cord.

Mayer and Liebeskind (1974) mapped the effect. Only stimulation of the central grey and the periventricular grey greatly reduced responses to painful stimuli.

The relief equalled or beat that of 10 mg/kg of morphine, an opioid painkiller. It did not come from the stimulation being rewarding. Many animals gave themselves the stimulation at high rates without losing pain.

The authors proposed that the stimulation switches on a pain-suppressing system that blocks transmission in the spinal cord.

Only three of the eight rats in Reynolds’s study showed relief, and rats are not people. Even so, it pinned the effect to one brain site.

Attention, Expectation and Reappraisal

Which thoughts change pain?

Wiech et al. (2008) reviewed brain-imaging research on this. They described three basic ways the mind changes pain: attention, expectation and reappraisal.

Attention engages the brain’s descending pain-control system, as in the gripping conversation of the shin example.

Reappraisal means changing what a pain means to you. It involves a front region of the brain, the ventrolateral prefrontal cortex, and changes the emotional significance of pain (Wiech et al., 2008).

Bushnell et al. (2013) reviewed the brain basis of this control. They also looked at evidence that chronic, or long-lasting, pain itself alters the circuits for pain control. That suggests control becomes harder as pain becomes chronic.

Expectation and the Placebo Effect (Levine et al., 1978)

Expecting relief is a clear case of the brain controlling pain. A placebo is an inactive treatment that people expect to help.

Levine et al. (1978) asked whether the brain’s own painkillers, the endorphins, are involved. Endorphins are morphine-like chemicals. The drug naloxone blocks opioids, so if endorphins produce placebo relief, naloxone should take that relief away and make the pain worse.

• Aim: To test whether endorphin release explains placebo pain relief.
• Method: Patients had impacted wisdom teeth removed. Three and four hours later they received naloxone or a placebo. Neither patients nor researchers knew which (a double-blind design), assignment was random, and pain was rated on a visual scale.
• Results: Patients given naloxone reported more pain than those given a placebo. The rise was entirely among placebo responders, people whose pain had eased with a placebo. Naloxone added no pain in non-responders.
• Conclusion: The results fit the idea that endorphin release produces placebo pain relief after dental surgery.

The study links belief to the brain’s opioid chemistry. It tested only one type of pain, and it did not show that the endorphin system is the whole mechanism.

Later brain-imaging studies traced the route.

In two experiments, placebo relief went with less activity in the thalamus, insula and anterior cingulate cortex (Wager et al., 2004).

Placebo relief also went with more activity at the front of the brain while pain was expected.

Eippert et al. (2009) combined naloxone with brain scanning. Naloxone reduced the placebo effect in behaviour and in the brain. It also broke the placebo-related link between the rostral anterior cingulate cortex, a front region of the cortex, and the central grey.

That link had predicted the size of the placebo effect.

Together these studies show a pathway from the cortex, the brain’s outer layer, through the midbrain to the medulla, at the base of the brainstem. It matches the central control the theory proposed.

They support the idea that, in placebo relief, the brain lowers pain through opioid pathways. They do not show that its signals act on the spinal gate itself.

Emotion, Catastrophizing and Fear

Emotion fits the gate model, in which signals from the brain can open or close the gate (Melzack & Wall, 1965).

Pain catastrophizing is a negative thinking and feeling response to pain that is happening or expected. The Pain Catastrophizing Scale measures it (Sullivan et al., 1995).

Quartana et al. (2009) reviewed several theories of how it works. They argued that it is an important process factor in pain treatment.

The fear-avoidance model proposes how fear can keep pain going.

It proposes that fear of pain can lead people to confront or avoid activity. It also proposes that avoidance can maintain or worsen pain and disability (Lethem et al., 1983).

The model is not part of the 1965 theory. It adds how seeing pain as a threat, and what people then do, can feed back on the brain’s control of pain.

Meaning: The Wounded Soldiers (Beecher, 1956)

The meaning of an injury may matter too. Beecher (1956) compared how often badly wounded soldiers and civilians recovering from surgery asked for pain relief.

Only 32% of the soldiers asked for medication. Among civilians with similar or less severe wounds after surgery, 83% did.

Beecher argued that for the soldiers the wound meant the end of the war and a safe return. For the civilians, surgery meant the start of a long, disruptive struggle.

This was an observation, not an experiment. Soldiers and civilians differ in age, fitness, injury type, setting and expectations, and Beecher could control for none of them.

It suggests that meaning matters without proving it. It came almost a decade before the gate theory offered a way to think about it.

What Is the Evidence for the Spinal Gate?

The theory makes a clear prediction about the spinal gate.

Adding touch input on its own should reduce the pain that small fibres carry. People tested this early. Genetic tools in mice later made a closer test possible.

The 1965 Paper (Melzack and Wall)

The paper is an argument, not an experiment.

• Aim: To explain how nerve signals about damage are coded, and why pain varies with context, without assuming that pain travels along one fixed line from receptor to brain.
• Argument: The model had to fit three facts. Small-fibre input is needed for pain. Few nerve cells respond only to intense stimuli. Pain varies with experience and psychological state.
• Claims: Large and small fibres converge on transmission cells and on a gating population. Large fibres close the gate, small fibres open it, and central control from the brain can tip the balance.
• Conclusion: Pain depends on a changing balance within the nervous system, not on a fixed channel.

The authors collected no new data. They combined findings from anatomy, spinal physiology and clinical observation into one circuit diagram (Mendell, 2014).

Its strength is that it made clear, testable claims, which is why it was so productive. Wall later said the paper provoked discussion and experiment (Mendell, 2014).

The limit is that the connections were inferred, not observed. Melzack and Wall noted there was no specific evidence for the single population of gate cells that large fibres excite and small fibres inhibit (Mendell, 2014).

Early Human Tests: Wall and Sweet (1967)

A test in people came two years later.

• Aim: To test whether stimulating large sensory fibres can abolish pain, as the theory predicts.
• Method: Eight patients with intense chronic skin pain had the sensory nerves or roots supplying the painful area stimulated with brief electrical pulses, 100 times a second. The voltage was raised until the patient felt tingling.
• Results: During stimulation, pressing on previously sensitive areas caused no pain. Four patients with diseased peripheral nerves had relief for over half an hour after only two minutes of stimulation.
• Conclusion: Stimulating large fibres could temporarily abolish pain, as the gate theory predicted.

The sample was small and had no control condition, so expectation and distraction may have helped. In the other four patients, who had no suspected nerve damage, pain returned within 5 to 10 minutes (Mendell, 2014).

A Human Test With No Effect (Nathan and Rudge, 1974)

Nathan and Rudge (1974) tested whether stimulating large nerve fibres in people stops pain carried by C fibres alone, as the theory implies.

They caused C-fibre pain in an artificial set-up. The limb had its blood supply cut off, and pain was caused with pressure, repeated pinprick, cold and heat. They then stimulated the nerves electrically, as is done to treat chronic pain.

They reported no change in the amount or quality of C-fibre pain, and no change in heat pain threshold. The authors found the results inconsistent with the theory.

This directly challenges one prediction. The limb preparation was artificial, so it cannot show that gating never happens.

Nathan (1976) followed with a critical review in the journal Brain. It cited conditions in which large fibres degenerate yet sensation is not painful, which undermined one of the theory’s founding assumptions (Mendell, 2014).

Wall (1978) replied. The reply accepted some of the criticisms but maintained that large-fibre inhibition was supported (Mendell, 2014).

Modern Tests in Mice (Arcourt et al., 2017)

Direct tests of gating became possible when genetic tools let researchers switch on, silence or remove defined spinal cell types in mice. Arcourt et al. (2017) used one such tool.

• Aim: To ask whether touch receptors contribute to acute pain signalling.
• Method: Using optogenetics, a technique that switches chosen nerve cells on with light, the team activated selected fibre types in mice, alone and together. They included myelinated pain fibres and touch receptors.
• Results: Activating the pain fibres alone caused abnormally strong pain responses. Activating touch receptors at the same time relieved them, in a way that depended on the frequency of the touch signals. A normal, well-coordinated reflex needed both.
• Conclusion: Normal acute pain signalling from pressure needs touch and pain input combined.

This is the closest modern test of the core claim that touch input can reduce pain. It used mice and acute, or short-lived, pain. The relief depended on frequency, which suggests the gate is graded rather than all or nothing.

Two earlier mouse studies identified spinal cells that fit the gate idea.

Foster et al. (2015) worked with inhibitory spinal cells, cells that hold other nerve cells back. They removed, silenced or activated them.

Removing or silencing them caused heightened sensitivity and excessive licking and biting of the skin. Activating them eased pain hypersensitivity after nerve damage.

This is strong causal evidence for a gating role, with defined cell types switched both ways. Licking is only an indirect marker of pain, though.

Duan et al. (2014) used genetic tools to mark and remove six types of spinal cell. Two stood out.

One type was excitatory, meaning it switches other cells on. Removing it caused loss of mechanical pain, which is pain from pressure on the skin.

The other type was inhibitory. These cells were needed to stop touch fibres from activating the excitatory cells and evoking pain.

The authors concluded that pain fibres, touch fibres and these two cell types form a small circuit (Duan et al., 2014). It passes on and gates mechanical pain.

All three studies are causal: each manipulates a defined cell population and measures behaviour. They are mouse studies, so whether the same circuit gates chronic pain in people is untested.

What the Evidence Adds Up To

Two parts of the theory have been tested: the spinal gate and brain control.

• Spinal Gate, Mice: Touch input and spinal inhibitory cells hold back pain signals (Arcourt et al., 2017; Foster et al., 2015; Duan et al., 2014).
• Spinal Gate, People: Mixed. A small uncontrolled study reported relief (Wall & Sweet, 1967), but the one experiment that stimulated nerves against C-fibre pain found no change (Nathan & Rudge, 1974).
• Brain Control: Two naloxone experiments on placebo relief support it (Levine et al., 1978; Eippert et al., 2009). Neither shows that the brain’s signals act on the spinal gate itself.

The evidence weighed here does not establish the 1965 diagram of nerve connections. Nor does it show that these mechanisms work together in the human spinal cord.

Strengths of the Gate Control Theory

The theory has four main strengths:

1. Testable Claims: It made clear predictions about fibre input and spinal circuitry that others could test, and it generated a research programme.
2. Mouse Evidence: Gene-based experiments find spinal inhibitory cells and touch input that hold back pain signals (Arcourt et al., 2017; Foster et al., 2015; Duan et al., 2014).
3. Brain Control: Brain stimulation and placebo experiments show the brain can regulate pain through descending pathways (Reynolds, 1969; Eippert et al., 2009).
4. A Wider View of Pain: It fits the biopsychosocial approach (biology, mind and social life all shape pain), which Gatchel et al. (2007) call the most heuristic, or idea-generating, approach in the field.

Mendell (2014) judges that the model was not correct in detail but changed how pain is understood.

Limitations of the Gate Control Theory

The theory has five main limitations. The first, second and fifth are explained in more detail below the list.

1. Wrong in Detail: Parts of the 1965 diagram of nerve connections did not hold up (Mendell, 2014).
2. Untested in People: The strongest evidence comes from mice, and the human tests are few and mixed.
3. Weak Treatment Evidence: Electrical nerve stimulation treatments built on the theory have inconclusive or negative trial evidence (Gibson et al., 2019; Traeger et al., 2023). Details are under real-life uses.
4. Explaining Too Much: Because it fits attention, emotion and expectation, it risks seeming to explain everything after the fact. A theory that can explain any result is hard to test.
5. Narrow Evidence Base: Most evidence on the mechanism comes from rodents, and most human work uses healthy volunteers in laboratory pain.

Wrong in Detail

Mendell (2014) judged parts of the 1965 model incorrect.

Nociceptors that respond specifically to damaging stimuli were found soon afterwards (Burgess & Perl, 1967). That fits the older idea of a dedicated pain line to the brain, a labelled line, better than the gate’s shared inputs.

Cells of the substantia gelatinosa turned out to be part of a system that sends signals on to other regions. They are not just a local gate.

The model drew the brake as acting on the incoming fibres’ endings, before the signal reaches the next cell. The inhibition may instead work in the receiving cell (Mendell, 2014).

Wall accepted that small-fibre input alone is not always painful (Wall, 1978). In other words, an open gate does not guarantee pain.

Mendell (2014) judges that the model changed how pain is understood even though parts of it were wrong. So the gate is a principle, not a diagram.

Untested in People

The evidence for a spinal gate comes mainly from mice. In people, the one test that stimulated nerves against C-fibre pain found no effect (Nathan & Rudge, 1974).

Clinical trials of transcutaneous electrical nerve stimulation (TENS), which sends mild current through the skin, do not record which nerve fibres the current activated.

Active TENS also produces a sensation while some placebo treatments do not, so patients may be able to tell which they have. A placebo comparison therefore controls for expectation only partly.

Johnson et al. (2022), who pooled many TENS trials, argue that blinding, keeping patients unaware of which treatment they received, was adequate. That is an argument, not a measured check. Even their combined result cannot rule expectation out.

Neither point tests the spinal gate in people. The evidence weighed here does not show that the mechanisms seen in mice work together in the human spinal cord.

Narrow Evidence Base

Most of the evidence on how the gate works comes from rodents. Most human work uses healthy volunteers in laboratory pain.

Chronic pain involves other changes. One is central sensitisation, in which nerve cells in the spinal cord and brain become more excitable and produce pain hypersensitivity (Woolf, 2011).

Do sensory differences change pain? Clinical accounts often say that autistic people feel less pain. The evidence is small.

Moore (2015) reviewed studies of acute pain and concluded that autistic people do not appear to have systematically altered pain responses or thresholds. Self-reports and parent reports tended to suggest reduced sensitivity. So did clinical observation. Observations of medical procedures and laboratory tests suggested normal or heightened responses.

Failla et al. (2018) compared 15 autistic adults with 16 non-autistic adults. Pain ratings and brain responses were alike during brief pain.

The autistic group showed a much weaker brain response during sustained pain, which the authors suggest may reflect different coping or evaluation.

Three cautions apply:

1. Small Samples: The studies are small.
2. Pain Scales: Standard pain scales may fit autistic communication poorly. A difference in how pain is expressed should not be read as a difference in how much it hurts.
3. Assessment: Pain assessment should adapt to the person, not assume that unusual expression means insensitivity.

How Is the Gate Control Theory Used in Real Life?

TENS

TENS, short for transcutaneous electrical nerve stimulation, applies mild electric current to the skin near a painful area. Its rationale follows from Wall and Sweet’s (1967) study.

Gibson et al. (2019) overviewed eight Cochrane reviews covering 51 trials of TENS in chronic pain. A Cochrane review gathers and assesses the trials on a question using strict methods.

These reviews were well done, but the trial evidence inside them was of very low quality. The trials were small and had major weaknesses.

The authors could not say with confidence whether TENS helps or harms.

Pooled trials tell a more positive story. Johnson et al. (2022) combined 91 placebo-controlled trials of strong, non-painful TENS. They found lower pain during or just after treatment. The reviewers rated their certainty as moderate.

The review included 381 trials in all. Only 26 were at low risk of bias, meaning few flaws that could distort results. Most were small (Johnson et al., 2022).

A mechanism can be attractive in theory while the trial evidence for the device built on it stays inconclusive.

Spinal Cord Stimulation

Spinal cord stimulation applies electrical pulses to the dorsal columns, which are largely branches of large sensory fibres. It also grew out of the gate theory. Shealy et al. (1967) published a preliminary clinical report.

Mendell (2014) calls the theory the genesis of this treatment. It is not clear that the theory explains its clinical effects, especially the lingering after-effects.

A Cochrane review of 13 trials with 699 people studied spinal cord stimulation for low back pain.

It concluded that the treatment probably does not improve back or leg pain, function or quality of life compared with placebo.

The placebo comparison is moderate-certainty evidence. It comes from a single six-month crossover trial.

The authors concluded that the data do not support using it outside a clinical trial (Traeger et al., 2023).

It is a clear example of a mechanism-driven treatment that has not met the evidence bar for chronic low back pain.

Cognitive Behavioural Therapy

If the brain controls pain, psychological treatments might help. Cognitive behavioural therapy (CBT) is a talking therapy that targets unhelpful thoughts and behaviours.

A Cochrane review of 75 trials with 9,401 people found that CBT had small or very small benefits for pain, disability and distress. CBT had the largest evidence base, with 59 studies (Williams et al., 2020).

Two other approaches were also tested. Behaviour therapy changes what people do. Acceptance and commitment therapy helps people live by their values despite pain.

Evidence for both was of moderate to very low quality, so their benefits are uncertain (Williams et al., 2020).

Mindfulness

Zeidan et al. (2011) tested mindfulness meditation in healthy volunteers after four days of training. Meditating during painful stimulation reduced pain unpleasantness by 57% and pain intensity by 40% compared with rest.

That is not a placebo comparison. Expectation could not be ruled out.

A later double-blind study found that mindfulness pain relief was not reversed by naloxone (Zeidan et al., 2016). That suggests it works differently from placebo relief.

For chronic pain, a meta-analysis pooled 38 randomised trials. A meta-analysis combines the results of many studies.

It found a small decrease in pain compared with all types of control (Hilton et al., 2017). The evidence was of low quality.

Hypnosis and Biofeedback

Thompson et al. (2019) combined 85 controlled trials of hypnosis for pain evoked in healthy people. It had pain-relieving effects on pain ratings, threshold and tolerance.

Threshold is the point at which a stimulus starts to hurt, and tolerance is how much a person can bear.

The effect depended strongly on how suggestible people were and on direct suggestions of relief. High-quality data in chronic pain are still needed.

Biofeedback gives people real-time information about a bodily signal, such as muscle tension, so they can learn to change it.

A meta-analysis of 21 studies with 1,062 patients found a small-to-medium effect on chronic back pain, stable over about eight months (Sielski et al., 2017). A meta-analysis of 53 studies of tension-type headache found a medium-to-large effect (Nestoriuc et al., 2008).

This supports self-regulation of pain. It cannot show that gate-like mechanisms are the cause.

Psychological therapies are best seen as a modest but real part of pain management, not a cure.

They sit alongside medical care, not instead of it. Anyone living with pain should discuss treatment with a doctor or other clinician.

Where Did the Gate Control Theory Come From?

Two Older Views of Pain

Before 1965, two views of pain dominated:

• Specificity theory: Dedicated receptors and fibres carry pain and nothing else. It is linked to von Frey.
• Pattern theory: The same receptors signal different sensations through different patterns of firing.

Melzack and Wall had already argued that specificity theory rested on three assumptions, about anatomy, physiology and psychology.

They doubted the psychological one, that a psychological experience could be matched to one type of receptor (Melzack & Wall, 1962; Mendell, 2014).

Melzack and Wall favoured a pattern-style view with central summation. In this view the central nervous system adds up the incoming signals.

The later discovery of nociceptors (Burgess & Perl, 1967) favoured some specificity. The gate theory added a regulated gate that neither older theory had (Mendell, 2014).

Three Clues Behind the 1965 Model

Mendell’s (2014) historical review describes three strands of evidence that fed the model:

1. Early experience: Dogs reared in a restricted environment reacted to intense stimulation but later failed to avoid it. Pain behaviour was more than the intensity of a stimulus (Melzack & Scott, 1957).
2. Shingles patients: Noordenbos found that shingles patients felt excruciating pain from gentle touch, and their affected nerves had a reduced share of large fibres. Noordenbos concluded that large fibres normally restrain small fibres.
3. Spinal experiments: Wall’s laboratory showed that signals entering the spinal cord can be controlled before they reach the next neuron, and that large and small fibres had opposite effects.

Anatomical work by Szentágothai added that large and small fibres enter the substantia gelatinosa from different directions (Mendell, 2014).

The shingles finding gave Melzack and Wall the idea that the balance between large and small fibre input decides how painful a stimulus is. The model did not need a special class of fibres that respond only to damage.

How Does the Gate Control Theory Compare With Other Accounts?

The biopsychosocial model is a general framework. It predicts that psychological and social factors matter for health, including pain. The gate theory supplies one mechanism by which they might (Gatchel et al., 2007).

The Neuromatrix: A Brain Network That Generates Pain

Melzack (1999) proposed the body-self neuromatrix, a widely spread brain network with parallel parts for body sense, emotion and relaying signals.

The pattern of the network’s output produces the experience of pain. Its inputs include sensory signals, thoughts and feelings, the brain’s own pain-dampening systems and the stress systems (Melzack, 1999).

Phantom limbs motivated the neuromatrix (Melzack, 1990). A phantom limb is the feeling that a limb is still there after it has been lost. Phantoms are common after amputation.

A complete spinal cord break can produce a phantom body below the break. A substantial number of children born without a limb feel a phantom of it.

That suggests the neuromatrix is partly built in at birth and then shaped by experience.

Flor et al. (1995) studied people after arm amputation. They used brain imaging to measure how far the brain’s map of the body, in the somatosensory cortex, had reorganised, or changed its layout.

They found a very strong link (r = 0.93) between the amount of reorganisation and phantom-limb pain.

A correlation cannot show which change causes which. The sample was also small. Even so, the study placed a pain mechanism in the cortex, not in the periphery.

The neuromatrix keeps the gate’s emphasis on the brain. It puts the generator of pain in a spread-out network.

That explains pain with no input from the body, as in phantom limbs (Melzack, 1999). It is less a rival than a widening of the same insight.

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