In the modern MIMO model of pain we see:

• Sensory Input Factors - Physical stimuli activating the receptors on the body surface, and travelling to junctions (Synapses) in the spinal cord, where the signal is transferred to other nerves that carry the signal up the spinal cord to the brain.  Supplementary information, on what else is taking place at the time, is also obtained from the bodies other senses, and passed onto the brain.
• Cognitive Processing Factors - The multiple regions in the brain involved in accessing other relevant information about the potential threat, and determining an appropriate response.
• Affective Output Factors - Nerve signals travelling back down the spinal column to execute the response.  This includes firing motor neurones to initiate movement and sending inhibitory or amplifying signals back to the synapses, to turn up or down the signals coming from the Neuroceptors.

The three factors were originally described by Melzack & Casey in 1968, are known as the three dimensions of pain, and as can be seen these factors are not independent but interact with each other.  We will now describe these three factors in more detail.

Sensory

For the Brain to determine what action to take in response to a pain stimulus coming from the peripheral nervous system, it must first obtain additional information on the nature of the threat and determine “how dangerous is this really”

The pain stimulus comes from the sensory neurons called nociceptors, which were discussed in the first article. Their function is to detect actual or potential tissue-damaging events and send a “danger” signal to the spinal cord.  Nocicepters respond to:

• excessive mechanical pressure, for example cutting, stretching or compressing tissue
• extremes in temperature,  > 45C & <15C
• noxious chemicals coming into contact with the body, for example acids or alkaline substances such as Capsaicin, which is found in Chilli Peppers
• chemicals released internally by damaged tissue (e.g. Histamine)

In response to the “danger” signal the brain evaluates a host of information coming from many of the bodies other senses.  This sensory information, which some have called discriminative information, provides the brain with knowledge of the location, intensity, duration and nature of the “threat”.  The senses providing the brain with information include the: 

• Eyes - Visual
• Ears - Auditory
• Nose - Olfactory

We will now look at some  examples of how the brain uses information from these various senses, during the threat evaluation, and how this information is interpreted or, in some cases, misinterpreted by the Brain.

The rubber hand illusion, is perhaps the most widely known experiment, showing how the brain interprets or misinterprets information coming from the senses.  This illusion demonstrates how:

• the threat response is not always related to tissue injury,
• the body’s other senses contribute to the response,
• the brain can be tricked into initiating a threat response where there is no real threat. 

In the rubber hand illusion, the brain is tricked into taking “ownership” for a rubber hand placed in front of a person.  As the  video below shows the brain is conditioned into believing the rubber hand is the person’s own hand, through tactile misinformation coming from stroking both the rubber hand & the person’s own hand at the same time, and from visual misinformation coming from placing the rubber hand where the person’s own hand would normally sit, and obscuring the view of the real hand.  The sense of ownership is so complete that when the rubber hand is hit by a hammer, or stabbed by a fork, the person is startled and rapidly withdraws their real hand.  That is, in response to the threat, the startle reflex and withdrawal response are initiated.

Other experiments or real life observations that demonstrate how the brain interprets, or misinterprets, information coming from the senses during pain related experiences are the:

• Nail Stories -  the contrasting pain response in the nail through the boot story compared to the nail through the skull story.  In the former, despite no tissue being pierced, the person feels intense pain due to the visual cues, while in the later no pain is felt due to the lack of visual cues.
• Binoculars Experiment - the finding that artificial manipulation of the size of a painful part of the body, influences the amount of pain a person feel after moving that body part.  In this experiment, those with chronic hand pain wore binoculars, which magnified or demagnified the image of the hand.  It was found that the demagnified images resulted in less pain being felt.
• Stretching Illusion - Where person’s with osteoarthritis wear video googles, and researchers manipulate the video signal to show the knee joint stretching out.   The researchers also give a slight pull on the calf muscle, as the knee is “stretched”. It is found this illusionary visual and tactile information tells the brain the knee has its normal range of movement, and relief from pain occurs.
• Q-Tip vs Needle Experiment - Further use of video to deceive the mind, by showing images of a person’s hand being pricked by a needle or touched with a Q-Tip (Cotton Bud), while simultaneously applying a painful or non-painful electrical stimulus to the hand.  It was found the pain experienced when viewing the needle was greater than that when viewing the Q-Tip.  Thus, pain is not directly related to the intensity of the injury, and is modified by visual input. This experiment also shows the role of expectation, which is discussed in the next section.
• Looking Reduces Pain Experiments - Experiments that show there is greater pain tolerance, when you look at the painful body part, rather than looking away.  That is, the more sensory information, the greater the pain tolerance.
• Phantom Limp Restoration - Where a person who is suffering phantom limb pain (the pain felt from an amputated limb), has their limb visually restored using a complicated arrangement of mirrors.  The agonising spasms were “cured” on “restoration” of the limb.
• Red vs Blue Light Experiment - The brain uses various cue signals to determine the level of danger.  In this experiment a cold bar was placed on a person’s hand, and simultaneously a red light or blue light was shown to the person.  It was found that for a number of persons the pain was greater with the red light, rather than the blue light, due to the association of the colour red with hot or danger.
• Sham HeadAche Stimulator - Where a person wears a skullcap on their head, & are told a headache would occur as a result of the electrical current they would receive via the cap.  They were then placed where they could see the intensity dial on a Sham Stimulator, and it was found that pain reports increased as the Sham Stimulator dial was “turned up”.
• Importance of language - It has been found that the language clinicians use to explain a person’s condition, or care-givers use to enquire as to a person’s well-being, can directly impact on the pain experienced.  For those with lower back pain, it has been found that when they hear language such as a “slipped-disc”, “buldging-disc”,”crumbling-spine”, “pinched-nerve” an expectation is set about the level of pain, and they feel greater pain.  Interestingly, imaging studies (e.g. MRI), show that the degree of physical abnormality in the image is not well correlated to the pain experience.   It is also found that the language used may desuade a person from engaging in treatment or undertaking activities positive to their well-being.  An example, is when the term “wear & tear” is used to explain the joint of someone with Osteoarthritis.

The above examples show how sensory information is used by the brain to evaluate the danger and regulate the pain experience.  In the above, we also started to see how expectation or prior experience also influences pain, and in the next section we look more deeply at these cognitive aspects.

Cognitive

From the previous sections, it was seen that when a threat is detected, the brain receives considerable real-time information from various parts of the body as to what is taking place.  The question the brain then needs to answer is “what does all this information actually mean, and how big is the threat really”.  Hence, the brain now engages in the cognitive activity of evaluating & apprising the information, putting the information into context, comprehending or understanding what it all means and then making the decision as to the most appropriate response.

The cognitive load of evaluating, comprehending & deciding what to do for every activity that takes place during a person’s normal day would be immense if the brain did this from the ground-up for every activity.  Furthermore the processing load would result in delayed decisions, which could threaten safety & survival.  For this reason, the brain takes “short-cuts” to make its best guess at what is going on and arrive at a timely decision.   We will explore below the cognitive process, the nature of the cognitive short-cuts, and see examples of how this can all lead to perceptions of what is taking place, which can be inaccurate and maladaptive.  The central nervous system also turns up or down the information coming from the sensory system, in an effort to ensure it listens to what it perceives to be the most important signals - we will discuss neuroadaptive factors, such as neuroplasticity, in a future article.

The factors influencing the cognitive process are:

• Attention - What else is going on at the same time? The brain has the ability to prioritise what activities it works on and, to reduce the processing load, it has the ability to filter out low priority information coming it way.  We consciously use this aspect of the brain when we concentrate or focus on a particular activity, or try to “think of something else”, when we are attempting to take our mind off something unpleasant.  Contextual elements, such as seeing someone else in pain, can also prime our brain or put us in a state of readiness, focusing our attention on a potential threat.  In the case of pain, attention is a two-way street, as the brain will divert our attention if something more dangerous or threatening is happening at the same time, however the greater the pain creating threat, the greater the pain signal, and the more attention we will give the threat or pain.  In the later case it can be very hard to fight our brain and divert our attention.
• Context - Where are we? What are we doing? What are we observing?  What are we expecting?   As indicated above the brain seeks information from multiple sources to get a better understanding of what is going on, and to assess the magnitude & priority of the threat.  It does not just rely on the information coming from the “pain nerves” (i.e. Nocicepters).  If something more important is going on, the brain focuses on the more important activity, which may mean little to no pain is felt from what would normally be a painful event.   The context also influences the experience through setting an expectation as to what will be felt.  Examples, of where context sets an expectation that modulates downwards the pain sensation, or creates a sensation other than pain, are intense sporting activities, deep-tissue massage, initiation practices & sadomasochistic sexual practices. Placebo analgesia, where people are given fake pain relief, is one of the best scientific examples of how context and expectation can modulate downwards the pain experience.  Conversely, as we will see in the next bullet, context also has the ability to amplify the pain sensation or to generate the pain sensation in the absence of a noxious stimulus.
• Memory - Have we been here before? What happened last time? How did we solve it? - The brain evaluates the situation based on past experience.  This includes evaluating what is occurring and deciding what action to take based on previous responses & the outcome of these responses.   The brain in effect builds up templates or preprogrammed models of behaviour to allow rapid threat recognition, evaluation and response.  Over-time these templates become generalised and as such, the best guess of what is taking place becomes less accurate.  In some cases, such as with chronic pain, the brain can produce a catastrophic interpretation based on a known pattern of sensory inputs, but in the absence of any threat.  For example, conditioned responses develop, such as the belief that any activity requiring a person to bend forward, or undertake certain activities, always causes back-pain.
• Cognitive State - Are we stressed, frightened, anxious, depressed, relaxed?  The regions of the brain responsible for pain & emotions are strongly intertwined.  This is an evolutionary consequence of the protective nature of the body’s defence mechanisms. For example, when something dangerous threatens the body the emotions of anger or fright can be produced, and the fight or flight response then initiated.  The unpleasant emotional responses associated with pain have the purpose of motivating the bodies defensive mechanisms to act and eliminate the threat.  These defensive emotional responses are intended to be short term, however, as an example, the fright emotion can transform into the longer term emotion of anxiety.  It is a common observation that anticipating, or feeling anxious about pain, exacerbates the pain experience.  It has also been found that suppressing anger can led to a lower pain tolerance and higher pain intensities.  Attention and mood have been found to influence the pain sensation differently, increased attention is found to increase pain intensity, while low mood tends to increase the unpleasantness of the pain experience. Thus, there is a complex cyclic interaction between emotions and pain.  The interaction is initially protective, but a negative compounding effect can develop where rumination and catastrophising develop with unhelpful exacerbation of the pain experience
• Cultural Values - What do we believe? What do others believe? Different cultures have different beliefs around the origins, acceptance, communication of discomfort, and treatment expectations of pain.  Cultural influences that are believed to influence the pain experience include religious beliefs, early life pain experiences such as corporal punishment, engagement in vigorous sporting activity, emotional response styles, biophysical views of ill-health & its treatment, social hierarchies and individualism vs collectivism.   For example, in some cultures where there is high stoicism or collectivism, reported pain ratings may be lower than in more expressive individualist cultures. There is also, clearly, a strong link between cultural factors and emotional factors.

Thus, the PsychoSocial Factors, which were previously discussed as influencers of the pain experience, sit within the cognitive part of the process.

Much of the resource materials around cognition and pain, and the above factors, are in the form of academic papers, with little simple plain english material available.  For the interested reader, the academic papers by Lumley et al on emotional factors, Anderson & Losin on SocioCultural factors and Moseley are useful reading.

As with the sensory information, the cognitive process within the brain has a strong and, at times, unpredictable (i.e. nondeterministic) influence on the pain experience.  There is the ability to misinterpret the information being received or for the brain to create preprogrammed decisions that produce unhelpful pain experiences or maladaptive threat responses. The following few examples, demonstrate the strong influence of the cognitive process on the pain experience & threat response:

• Context (Physical) - There are many war-time stories, & the classic report by Beecher, where soldiers either felt no pain from grievous injuries suffered on the battle field; little pain from major injuries suffered on the battlefield but felt significant pain when minor procedures were performed at home; or where war-time injuries associated with bullets & shrapnel being lodged in the body were not discovered until many years later. In these situations, the soldiers where in a context where their very survival was under-threat and, it is believed, the brain prioritised this survival over “mere flesh wounds”. 
• Context (Expectation) - In a study with patient’s with Alzheimers disease, it was found that the placebo analgesia mechanism was disrupted with prefrontal lobe tissue degeneration.  It was also found that the disruption of the placebo analgesic affect also made analgesic therapies less effective in these patients.
• Memory -  In the video above Lorimer Moseley tells the amusing story of how he suffers a snake bite, while walking in the bush, and how memory of similar experiences can results in a muted reaction to the snakebite, but over-reactions to similar benign experiences afterwards.   
• Cognitive State - It was suggested in the war-time reports above that the patients may have also felt no pain due to the enormous relief, and euphoric feelings, that resulted from now being free from a dangerous environment, full of fatigue, discomfort, stress & content anxiety.
• Cultural Values - In Nepal back pain is not thought of a health issue, it is thought to be part of the normal ageing process, and so medical intervention is not sought even when it is freely available.

Affective Output Factors

Once the body’s protection system has determined a real danger is present, and that addressing this danger is of utmost priority, it initiates actions from a number of the body’s many protective mechanisms.

To protect the body, the body will then initiate reflex or preprogrammed type actions, or create (affective) feelings and sensations within the body (e.g. pain) to motivate the individual to undertake protective actions.  Thus, there are protective behaviours or responses of which we are aware (e.g. pain) and others that automatically occur, often within the body, of which we are largely unaware.

The reflex and preprogrammed type actions, serve to (rapidly) remove the individual from the threat and to turn up the internal systems within the body that are required to address the threat or injury, while turning down the systems that are not required at that time.  The reflex and preprogrammed type actions include the:

• Reflex movements, such as the the withdrawal response when a hand gets too close to a stove element or a hammer is about to hit the hand, as in the Phantom Hand Illusion described above.   Once the nervous system detects danger, its first action is to send signals to contract the relevant muscles.  Contraction uses the energy (adenosine triphosphate (ATP)) already present in the muscle’s cells.  A muscles supply of ATP is only sufficient to power vigorous movement for 2-3 seconds.    These reflex movements occur prior to sympathetic nervous system activating the adrenaline driven fight, flight or freeze response, which is briefly described in the video below.
• Initiation of Endocrine Signalling, which is one of the body’s main forms of chemical signalling.  Various hormones are pumped into the blood stream, and these hormones then travel to the body’s various organs to either turn up their essential functions and turn down their non-essential functions.  Endocrine signalling is initiated by the sympathetic nervous system, and has a response time slower than the electrical based signalling of the nervous system, and this is why the first reflex actions are initiated by the nervous system.
• Autonomic response, where the hormone Epinephrine (Adrenaline) is released into the blood from the adrenal gland sitting on top of the kidneys, in response to the signal received from the brain over the sympathetic nervous system.  Adrenaline prepares the body to deal with any ongoing threat, by raising the heart rate, increasing blood pressure, increasing breathing rate, dilating air passages, constricting peripheral blood vessels to concentrate blood supply to the body’s main organs and large muscles, dilating pupils to improve low light vision, sharpening hearing, decreasing blood flow to the frontal lobe of the brain, increasing blood flow to the instinctive/primitive part of the brain, and decreasing sensitivity to pain related signals. In this high arousal state, which is focused on survival, rational decision making capability is reduced with blood flow away from the frontal lobe, tunnel vision occurs, skin goes pale, and the periphery of the body feels cold
• Stress response, where the brain triggers the release of the hormone Cortisol (the stress hormone) into the blood from the adrenal gland.  It does this when it considers the threat to be ongoing and the initial adrenaline based response, which lasts about 20mins, to be insufficient.  Cortisol is both a hormone and a steroid.  It take minutes rather than seconds to feel the effects of Cortisol release.  Cortisol drives the release of anti-inflammatory factors into the blood, increases available energy supply to the body by increasing blood sugar (glucose), increases blood pressure, increases alertness through its role in regulating the sleep/wake cycle, and turns down the immune system, digestive system, sexual desire, reproductive system & growth processes.
• Nonessential systems being turned down as described above.  These suppressed systems include food digestion, sexual desire, pain response, rational thought processes, energy consuming inflammation & healing processes
• Immune response, is a secondary response, where adrenaline signals to the body to release into the blood the major pathogen fighting immune cells (i.e. monocytes, lymphocytes & neutrophils),and then later Cortisol signals to the body to release pro-inflammatory factors (cytokines) and to push the immune cells that have been circulating in the blood out of circulation into the affected site(s).  There is some debate on whether the fight or flight response suppresses or enhances the immune response, but this could just be subtleties around when these cells reach the affected body part.  There is agreement, however, that prolonged stress response can compromise the immune system.
• Adaptive modulation, is also largely secondary response taking place in the nervous, endocrine and immune systems, where peripheral, organ based, and brain based systems are sensitised or desensitised. For example, when tissue is injured, the nociceptors in the surrounding area are sensitised with the release off inflammatory mediators such as histamine & serotonine.  The purpose of making the surrounding area more sensitive to painful stimuli is to motivate the person to protect the injury site. Where the nociceptors met the spinal cord the signals can be desensitised by the local opioid and cannabinoid systems providing natural analgesia, and from desensitising control signals being sent from the brain.   Neuro-modulation and neuroplasticity is a subject in its own right and, as indicated above, will be discussed in more detail in a follow on article.

From the above, you can see that much happens rapidly in the body’s protective system, and in systems closely aligned to the pain system, in a manner that is unconscious, uncontrollable and that turns down the more rational control mechanisms of the body. 

The body is retuned to is normal calm state by the parasympathetic nervous system.  This is the brake that returns the body to equilibrium (homeostasis) as compared to the sympathetic nervous system that is the gas-pedal.   It can take up to an hour to calm down from the adrenaline rush.  These systems can also malfunction, and people can stay in a heightened state longer-term, where the effects of the hormones have a negative effect on their life & health.  An example of this is chronic activation of the stress response.

The affective or motivational sensations, are the various unpleasant feelings or sensations that we call pain. The unpleasantness of these sensations provides a strong drive to undertake protective actions to avoid danger or get the body’s tissues out of danger.  The affective motivational experience we call pain:

• As discussed here, is in an output of the brain, with the intensity of the Pain being correlated to the perceived threat, and not the actual tissue damage. 
• Has a characteristic called motivational dominance, which is the degree to which the unpleasant sensation drives protective behaviours with urgency.  Motivationally dominant sensations are difficult to ignore, and repetitively interrupt “non-protective behaviours”.  The motivational dominance of pain provides some insight as to why chronic pain can be difficult to ignore and can disrupt a person’s everyday life.   
• Can be felt whenever there is a threat of tissue damage, and not always when there is actual tissue damage.  This ability to generate pain in response to anticipation of tissue damage was alluded to above in the discussion on cognitive factors.  This anticipatory function is thought to be an evolutionary development designed to have us avoid dangerous or risky behaviours or situations likely to result in tissue damage.
• Comes in an array of unpleasant sensations, including stabbing, aching, throbbing, stinging, burning, shooting, or tingling.  As indicated in our first article, the sensations are often linked to the origin & cause of the pain. For example, tissue damage tends to result in sharp, aching or throbbing pain, while nerve damage tends to result in burning, shooting, numbness, tingly and highly sensitised sensations.
• Exists across a spectrum or within a Sensation Output Space, where different sensations have different levels of awareness, different levels of unpleasantness and different levels of motivation to take action.   For example, severe pain is a sensation of which we are acutely aware, find highly unpleasant and are highly motivated to take action to mitigate.  The dead arm with the mildly unpleasant pins & needles sensation, which wakes you from your sleep, and then motivates you to move your body off your arm to remove the source of the nerve & blood vessel compression, and then move the arm to get the blood flowing again.  Whereas, the muscular dullness that develops a few hours after a long bike-ride, is something we only become aware of when we start to relax at the end of the day, could be considered to have a satisfying feeling, and there is no strong motivational drive to protect the legs with a welcome rest being seen as the “cure”.
• Play a very similar role to some of the bodies other protective or survival sensations, such as thirst & hunger for food, hunger for air, sexual desire, desire for sleep, disgust, sickness & itch.  The purpose of these sensations is to drive the person to avoid doing something or to undertake a certain action to protect or survive.  The driver come from the pleasant experience obtained on undertaking the activity (i.e. the reward) or the relief that comes removing the cause of the sensation (i.e. the punishment).  As indicated above, the sensations we feel exist in a sensation output space, from various types of pain and other unpleasant feelings such as nausea, through more neutral feelings such as itch, and then through to more pleasurable sensations. The body’s nervous system is also heavily involved in sensing and driving these behaviours as is the endocrine system, through hormones and neurotransmitters such as dopamine, adrenaline, cortisol, endorphins, and serotonin.  Neurotransmitters are chemicals involved in the firing of neurones, and some chemicals can be both a hormone and neurotransmitter.

There are a number of experiments or observations, that demonstrate how the output aspect of this system functions, and in some cases malfunctions.  Examples include:

• Threat sensitisation, which many of us have experienced in recent times around natural disasters or other mass casualty incidents.  For those of us who experienced the Christchurch Earthquake, many of us experienced the ongoing sensitisation of our protection system, and the accompanying heightened arousal & anxiety.  Our heightened state, or hyper vigilance, was evidenced by our stress response ramping up to normally innocuous events, such as the ground tremor that occurs when a truck or bus drives past.  It is usual for our system to reset to “normal levels” within a few months, after such experiences, but for others longer term effects were seen with anxiety and Post-traumatic Stress Disorder
• The masochist experiment, where the sensation reported by the participant in response to a common stimulus, was reported as either painful or pleasurable, depending on the context in which the pain was inflicted.  In these experiments those with an interest in masochistic sexual practices were recruited alongside a group of control participants, and in one study visual images including those of masochistic practices were presented to participants, and in another study (19min in video) researchers or a Madam read a script describing the pain stimulus about to be applied.  Both studies found that Masochists did not feel pain when presented with masochistic images or the Madam read the script.
• Benign masochism, which is the term some use to describe partaking in normally painful activities such as extreme exercise or chilli eating.  In this activities, it is thought, pain is endured to stimulate the body’s protective system, and receive the natural reward from the body's opioid or cannabinoid systems, or the practice is learnt to no-longer be associated with harm.
• Prosthetics simulating protective properties of pain, where pain stimulators were developed for persons with Leprosy in an effort to drive behaviours protective of the limb(s) they can’t feel.  It was found that this prosthetics were ineffective, as the motivational aspect of the pain sensation was missing & the person over time learnt to ignore the pain stimuli.
• Motivational dominance of pain, where the drive to attend to intense pain was seen to override or impact on the ability of people to perform other tasks.  In these experiments, people were given tasks of varying levels of cognitive demand while applying pain of varying levels of intensity.   It was found that when pain was intense and task demands high, the ability to perform the task at hand was severely impacted.
• Motivation dominance of other sensations, where as an example the drive created by the chronic itch of eczema, or insect bites, is relieved by scratching that in turn creates open wounds and pain.
• Phantom Limb Pain cure with mirrors, where there is a theory that Phantom Limb pains is cured by mirrors restoring the relationship that should exist between the limb moving, sensory feedback saying it has moved and relief from pain following.  Normally, with Phantom limb pain, an incongruecrency exists between body’s intention to act by moving the limb to alleviate the pain and the sensory feedback that the limb has done so.

Chronic Pain is Real

As we have seen here, pain is a sensation & emotion wholly created in the brain, and not created in the damaged tissue.  The chronic pain sensation is almost always not directly related to tissue damage or the severity of that tissue damage.  Pain is one output of the of the system that the body has in place to protect & ensure survival.  This system contains multiple subsystems (e.g. peripheral nervous system, central nervous system and brain) and functions alongside multiple other systems (e.g. endocrine & immune) that also have a role in protection & survival.  All of these system operate not just in the present, but also operate on information from the past & predictions of the future.  It has been seen that many parts of these systems can misntepret information, become maladaptive, inaccurately determine the magnitude of the danger, and become overly sensitised.  All of the effects discussed in this article are real physiological effects.  Hence, when the pain system gets out of kilter or goes wonky, and Chronic Pain develops as a result, the Chronic Pain felt is real, is of physiological origins and is a disease in its own right.  Chronic Pain itself is the problem, and not just a symptom.   

In summary, when trying to understand Chronic Pain, it is useful to keep in mind that

• The pain is real and comes from real physiological origins
• It is simply your body trying to protect you
• Tissue damage is not necessary for you to feel the pain sensation, as your body’s protective mechanism acts in response to the threat of potential harm
• Some aspects of the pain-response are pre-programmed or are reflex type actions, which means that no conscious evaluation of the threat takes place.
• When pain is severe it can be very hard or almost impossible to ignore, due to the strong motivational dominance - the drive the sensation creates for you to act in a manner which protects your body.
• We have seen that there are many places where the overall system can malfunction
• The body’s protective system, which the pain system is a key part, comprise the body’s nervous, endocrine & immune systems.  These systems are interlinked, have common components (e.g. hormones & neurotransmitters) and act interdependently.  Thus, malfunction in one system can cause other systems to also malfunction.
• The protective systems, because of their memory based generalised models can produce prediction errors as to the nature & size of a threat.  This is a bit like a smoke alarm, that is a warning system that will respond to burnt toast, steam from the shower or a house fire.
• The protective system may not correctly reset after sensitisation, and when this type of malfunction occurs the body may remain in a heighten state of alert or the inputs to it senses may remain magnified.

A useful aid in understanding the pain system, is to consider its parallels to the body’s other protective and survival systems, such as the stress response system, hunger response, thirst response, hunger for air, disgust response, feeling of sickness, sexual desire & itch.  All these systems create strong motivational sensations that drive protective or survival responses.  Each of these systems can malfunction, and many are interrelated in some way to he pain system, with malfunction within these systems impacting the pain system, and vice versa.  In a follow-up article, we will take a deeper look at this other systems and how they also can malfunction, how this malfunction disrupts an individual’s life, and how these malfunctions can relate to the pain system.

Now we have an understanding of the factors that can influence the pain experience we can start to discuss diagnosis & treatment.  It is clear Chronic Pain is a highly complex condition requiring a holistic understanding of the body and mind.  It is also an area of medicine that is currently evolving as we understand more.  The next two articles in this series describe:

• What is Best Practice Treatment
• The Interdisciplinary Team, their roles & contributions