Our Blogs

Matrix, Keena Reeves, No No, this is Neuromatrix: For Pain.

As we discussed in a previous blog, due to constant efforts of researchers and scientists, we have a better understanding of pain science. Currently, the neuromatrix model developed by Ron Melzack, psychologist, is clinically the most useful model of pain. The model opines that pain is output from the brain based on multiple sensory input our brain receives. This sounds simple, but it is not. So, 

Grab your coffee or tea, and get ready to dissect the neuromatrix model to have a deeper understanding of pain science.  Below is the conceptual framework of the Neuromatrix model.

At first glance, my basic understanding of this model is that various inputs (left side of diagram)  reach the body self neuromatrix (which is our nervous system: nerves and brain). The body self neuromatrix conducts an executive function of analyzing, processing and evaluating the input, and finally produces output (right side of diagram). 

Zooming in to Input Side:

A) Sensory-Discriminative Input: 

This is the middle input on the left side of the diagram which includes all the sensations felt and perceived by the brain/nervous system at any given moment of time, arriving from different sensory organs.

1. Five Basic Senses:

• Vision
• Touch
• Taste
• Smell
• Hearing

Additionally, our nervous system also receives input from

1. Proprioceptive mechanism: a special kind of receptors, called proprioceptors, in our joint which brings awareness of our body parts in three dimensional space. For example, if you close your eyes and move your right hand out, your brain can recognize that your right hand was moved outward without input from your eyes. Thanks to proprioceptors. 

2. Vestibular system: A structural unit in our inner ear which is responsible for maintaining balance and equilibrium. In addition to the vestibular system, vision and proprioception are other systems responsible for equilibrium.

3. Interoceptive system: This system provides input to the brain regarding the sense of physiological state of the body at any given moment. It’s like how fast your heart is beating, how much oxygen is passing through lungs, what is the internal temperature in your body and so on. Most of the time, we are not consciously aware of this system. It is automatically happening all the time.      

Depending on what task our brain is conducting at a given moment, some sensory inputs are brought to conscious awareness while some are completely filtered out. 

B) Cognitive-Evaluative 

This class of input on the left top side which includes all the beliefs and concepts about pain from past experience or learning. Additional, an individual personality, culture and mental state of mind can also provide input to the body self neuromatrix

C) Motivational-Affective

Emotional state and hormonal secretion at any given time also modulates or provides input to the body self neuromatrix. Constantly the A and C section on the input side of the neuromatrix provides the feedback to the body self neuromatrix, mostly unconsciously.  

Body-Self Neuromatrix

In the center of the neuromatrix, there is a circular zone which represents our nervous system (central and peripheral). Melzack describes the neuromatrix as a widespread network of neurons that consist of loops and connections to the different parts of the brain. This network of neurons is initially determined genetically and later sculpted by sensory inputs (taken from Melzack article so provide reference). The body’s self neuromatrix is a cyclical process (indicated by circular arrows), which means that it constantly changes based on various inputs, and therefore output also changes constantly. This repeated cyclical processing and synthesis of constant nerve impulses produces a characteristic pattern, known as neurosignature. I know you might be wondering, hmmm, what is neurosignature? We will discuss neurosignature later, but right now let’s check the right side of the neuromatrix, which is output

Output

Pain is on the top right side of the diagram. So, pain is the output from the body self neuromatrix. After thorough analysis, from various inputs from the left side, the body self neuromatrix comes to the conclusion that, at this given moment, there is more credible evidence of threat than safety. So let’s generate pain in order to take some protective action. Now, as an individual who experiences pain will try to dampen this sensation by moving a particular body part or might result in a complex movements to reduce or diminish the sensation of pain (you might have noticed that you move your body or change position to find that comfortable spot where there is no unpleasant sensory experience: pain). Additionally, as coping strategies other physiological changes occur in our body such as, secretion of certain hormones and immune system response to achieve the homeostatic balance in the body. 

Now the output: pain, movement and physiological changes, will further generate a new sensory event, which again flows through the body self neuromatrix. The body self neuromatrix will do the analysis and synthesis of these neural impulses and the next output is generated. This continuous dynamic cyclical process continues and constantly modifies the body's self neuromatrix. Most of the time this dynamic process is occurring unconsciously that we are not even aware about. 

Neurosignature: 

It is a characteristic pattern of synaptic connection with different parts of the brain which is developed within the body self neuromatrix. Think of it as a bundle of neural loops or networks of any particular event. For an instance

Mr Mehta experienced pain in low back while bending forward to pick up a towel. Simultaneously, he heard a loud pop sound. At this moment, Mr Mehta was at the workplace. Now let’s break down the input, output and body self neuromatrix for this particular event. 

Sensory input from proprioceptors (remember, the special receptors between the joints), along with the other sensory input, like pop sound and workplace environment, will reach the brain (body self neuromatrix). The brain will also try to retrieve additional information from other centers, like amygdala (threat detection center), hypothalamus (collection of past memory, ah my aunt had similar sound in her back and she is paralyzed right now), prefrontal cortex (cognitive, decision making region), and many other regions. Based on this collective information, our body self neuromatrix comes to the conclusion that is there credible evidence of danger/threat or not? Depending on yes or no, there will be necessary output: Pain or No pain.

Now this entire loop of neural networks for this specific event at a particular moment is categorized as Neurosignature. So there can be many neuro signatures embedded within the body self’s neuromatrix. Interestingly, each individual will have a unique neurosignature pattern, and therefore each individual has unique pain experience. Hmm, could that be the reason why a certain movement generates pain for a particular individual while the same movement is absolutely fine in another individual. 

Pain is weird, right? Yes, Pain is a unique contextual unpleasant sensory experience. 

In an individual, there will be a unique neurosignature pattern for specific event. So, multiple event will result in multiple neurosignature within the body’ s self neuromatrix. In some people, a particular component of neurosignature constantly remains active, triggering the cascade of neural impulses resulting in a repetition of specific output: pain, abnormal movement pattern, muscle spasm and so on. Ultimately leading to a phenomena described as Central Sensitization. 

Well, we will deal with Central Sensitization in another blog, but for now I hope the concept of Neuromatrix pain model makes sense to provide a little more insight about persistent pain.