Pain is a unique subjective experienced that is influenced by factors such as cultural learning, personal significance of the situation and attention (Melzack 2001). When pain is experienced, it usually indicates injury, disease and threats to body tissues (Mosley 2003 & Butler & Moseley 2013). However, complexity of pain perception increases when considering chronic or phantom limb pain. Simply, these types of pain are indicative of the neural mechanisms gone awry, thus, alter perception of what is occurring in the tissues (Moseley 2003).
For example, chronic pain can be ongoing years after an injury has een healed by the body, so the pain felt is not physical damage but rather what the brain perceives as pain signals (Melzack 2001). Additionally, phantom limb pain is perceived to originate from a limb that isn’t there, although, the pain sensation is still felt (Melzack and Katz 2006). These conditions provide the foundation of the neuromatrix theory. The theory proposes that pain is a multidimensional experience produced by patterns of nerve impulses, called neurotags, over a widely distributed neural network, ‘the body self neuromatrix’ (Melzack, 2005).
There have been many theories created to explain pain, each eing improved on to produce the modern Theory of the Neuromatrix (Melzack 2005). The Specificity Theory proposes that pain impulses are transmitted along linear pathways to pain centres in the brain. The intensity of the pain is determined by the number of impulses along a neuron (Moayedi & David 2013). This theory fails to consider psychological effects such as past experiences and anxiety that can act to alter pain perception (Melzack and Katz 2006).
The Gate Control Theory emphasised a ‘gate mechanism’ at the dorsal horns of the spine to modulate synaptic input to the brain for processing (Melzack 003). The gates opening is determined by the diameter of the active peripheral axons whilst the dynamic action of the brain acts to ‘close’ the gate (Keefe et al. 1996). This theory is effective in combining peripheral sensory information with top-down information from the brain, but does not provide a sufficient explanation for phantom limb pain (Melzack and Katz 2006).
The Neuromatrix Theory provides an explanation for complex pain problems, is founded on input factors such as sensory, affective and cognitive neuromodules generated by the body-self neuromatrix (Melzack 2001). The output pattern produces multiple dimensions of awareness in addition to concurrent behavioural movements and homeostatic responses (Melzack and Katz 2006). The neuromatrix is individual for each person, it is comprised of a network of neurons and synapses within the brain whose spatial distribution is determined genetically but shaped and remodelled by subjective sensory experiences (Keefe et al. 996).
An extensive network of intertwining neural connections between the thalamus, cortex and the limbic system bounce information backwards and forwards, implying hat pain perception is affected by inputs such as sensation, movement, emotions and memories (Keefe et al. 1996). Interesting features of the neuromatrix theory propose that it extends beyond the physical body schema, and that conscious awareness and perception of self are generated within the brain (Melzack 2001).
It is because of this feature, that pain perception is to be viewed as an output generated by the neural network rather than as a result of sensory input (Melzack 2001). Inputs, generate nerve impulses that converge and diverge to create characteristic patterns, called neurotags (Melzack 2001). It is the neurotag of a specific body region which determines how it is consciously perceived. For example, several input systems contribute to the pain neurotag such as; somatosensory, limbic and thalamocortical system (Moseley 2003).
Neurotags are inputs of continuous outflows of nerve impulses which is converted into a stream of awareness once it is projected onto the sentient neural hub in the brain (Moseley 2003). Patterns of movement can be produced as an additional response via bifurcation of the neurotag. Information is transmitted to the sentient neural hub in addition to the spinal cord to activate eurons responsible for muscular patterns, thus bringing about the desired goal (Moseley 2003).
The neuromatrix excels in describing the necessity of unity between sensory, affective and cognitive inputs to produce pain outputs such as perception and action (Louw et al. 011). This is key in understanding how clinicians effectively treat a patient’s pain holistically (Louw et al. 2011). Using the neuromatrix theory, patient’s pain perception can be reduced via altering the negative inputs to the body-self neuromatrix which has a corresponding output effect (Moseley 2003). Clinician’s often use different mechanisms to desensitise the neuromatrix by altering inputs such as cognitive-related experiences, emotional-related brain and sensory signalling systems (Moseley 2003).
Desensitisation of the neuromatrix can occur in many forms. Validation of a patients pain in addition to reassurance that the body is no longer in danger can reduce the cognitive and emotion-related brain areas input into the neuromatrix (Melzack 2001). This reduction of negative input then reciprocates with a positive shift in output experienced as pain perception (McAllister 2015). This is an effective tool that acts to empower the patient and allows them to take control of their own treatment (McAllister 2015).
Clinicians can employ this same principal when treating chronic pain sufferers. The defining feature of chronic pain is the duration of suffering and the resultant psychological stress which increases the pain experienced more than the physical disability alone (Moseley 2003). With persistent pain, the nociceptive system and the virtual body undergo changes which strengthens the neuromatrix and increases the sensitivity to inputs, thus less input results in pain (Melzack 2001). The most effective tool a clinician can use is education on the complexity of pain mechanisms.
Studies show that even basic understanding of the principals and theories associated with pain have positive influences on patient’s pain levels, function and healing times (Louw et al. 2011). By understanding the factors that make up inputs into the neuromatrix the patient is equipped with the necessary information to alter their own pain perception (McAllister 2015). For example, the patient is able to reduce negative input from the cognitive-related brain area by iving new meaning to an old memory that once negatively affected their chronic pain.
By reducing a ‘threatening? input, a reactive response changes pain perception in a cognitive dimension (Melzack 2001). Furthermore, distraction has been shown to be an effective tool in decreasing pain for both acute and chronic pain sufferers (McAllister 2015). Cognitive intervention draws the patient’s attention away from the pain which they are experiencing, thus reducing negative input from cognitive-related brain areas into the neuromatrix areas and creating a corresponding reduction to the overall perception of ain (McAllister 2015).
The neuromatrix theory can be utilised to discover patient’s pain-free threshold as a platform to make incremental improvements. By reducing negative input into the neuromatrix, activation of neuromatrix, but not stimulation of the pain neurotag can be achieved, thus creating a baseline (Moseley 2003). This same principle can be used to make progressive improvements by increasing the threat load in the form of physical, contextual or emotional inputs, thus maintaining an inactivated pain neurotag yet not overloading the patient (Mosley 2003).
The neuromatrix is a successful theory that enables clinicians to effectively describe the mechanisms of phantom limb and chronic pain. The theory encompasses the importance of sensory, affective and cognitive neuromodules interacting within the body-self neuromatrix to produce outputs of pain perception and action patterns. This theory can be modified and implemented in the treatment of pain. By manipulating various inputs, such as cognitive, emotional and sensory contributions into the neuromatrix, clinicians and patients alike are able to alter the outcome of pain perception.
