We spoke in our last post about how our life experiences have shaped the way we receive, perceive, and respond to life's stressors. But how does this learning process unfold and morph into our personal pain perspective? In order to understand this we've got to delve into the world of our nervous system. Don't worry though we don't plan on getting too deep into the "neurological abyss". Just enough to shed some light on the topic of pain and our brain.
Before we begin our journey there's a very important caveat you need to keep in mind. At this point in time no one "knows" exactly how the brain works; however, many of the current theories do have common threads. These common threads, when stitched together, lay a sort of tapestry detailing how our nervous system more than likely works. It is from this foundational tapestry we will pull from for this discussion.
The Journey Begins...
Without any further adieu, let's dive in. We'll go first. The nervous system is divided into 2 broad classifications: the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system includes the brain and the spinal cord; whereas, the peripheral nervous system is made up of our peripheral spinal nerves (those outside the spinal cord) as well as our cranial nerves. It is the job of the PNS to liason between the CNS and the rest of the body. The PNS is further divided into a sensory (afferent) and motor (efferent) division. The motor division of the PNS is then divided into the autonomic (ANS) and somatic (SNS) nervous systems. The ANS is further divided into the sympathetic and parasympathetic divisions. You still with us? We're almost as deep as we are going to get, hang in there. We'll level off soon. Take a look a the graphic below, I've summarized what we've just discussed.
The afferent fibers (those in purple) are nerve fibers that send information to the brain. This information is gathered by a number of receptors throughout the body. The afferent information is then used by the brain to determine the "correct" course of action to take. It is through the efferent fibers (those in green) that the brain sends information toward the periphery in an effort to promote or prompt a particular action to take place. The brain itself is a vast network of neuronal, immune & vascular cells that communicate with one another through electrochemical as well as molecular mechanisms throughout our lifetime.
It is through these interactions between cells within the brain that are continuously creating and or modifying "networks" throughout the brain for specific actions. In fact there are various collaborations and competitions going on in your brain right now. Collaborations are when groups of cells work together for a specific purpose; whereas, at the same time other cells are competing with some of the same cells within a given network to make new connections for other purposes. It is through this give and take of collaboration and competition that the brain is said to have redundancy. Redundancy is the ability of our brains to have a number of alternate ways to accomplish the same task. Think of this as being able to have a back up plan in the event your original plan fails.
Redundancy is made possible through distributed processing, which is the brain's capacity to form parallel networks that stretch across multiple areas of the brain, rather than just being localized to one region or another. Once a group of cells in collaboration "fire together, they wire together" creating a specific network of cells distributed throughout multiple regions across and throughout the brain. The more we 'run' a given network the stronger that network's communication becomes and consequently the more influential it's action. Think for a moment about that one nagging habit you've tried so hard to change over the years. That distributed network has been fired so often that its collaboration as well as its affect on you is extremely influential.
Something we also now know is that our neural networks aren't as fixed as we may have once believed. In fact through intentional, or even unintentional beliefs, thoughts and actions these established networks can become 'wired' or even 'rewired' as directed. This "retraining of the brain" is termed plasticity and is instrumental in our bodies function. Plasticity is the reason, for instance, a person who suffers a stroke affecting one side of their body is able to regain some, if not all, of their function following the stroke. Throughout their recovery process along with some intentional efforts the brain begins rewiring creating new connections with cells that weren't damaged to create a "work around" from the original yet now dysfunctional network.
How amazing is that?? Our brains have the ability to organize and reorganize as needed...very cool!
Ok. That's great, but how does this relate to the brain and pain?
Based on this information two extremely knowledgeable folks in the world of pain science, David Butler and G. Lorimer Moseley, have described this theory in great detail. In their book Explain Pain Supercharged (2017), they describe these collaborations and competitions between cells as a process by which a given set of 'neurotags' or specific neurons come together creating collaborative networks. According to this conceptualization there are two broad types of neurotags working within our brains: 1) Action (primary) neurotags; and 2) Modulation (secondary) neurotags.
An action neurotag has influence beyond the brain (e.g. muscle) as well as on any system that also exerts influence outside of the brain (e.g., consciousness). Modulation neurotags on the other hand only have influence within the brain. These are "things we know that we don't know we know" which have a profound effect on the way we do things. Examples of these include previous exposures, characteristics of people or places, etc. It is the modulation neurotags that can significantly influence an action neurotag which will then impact our overall output such as our movement quality or overall pain experience.
As discussed above, afferent signals are messages from the PNS that are sent by receptors whose job it is to detect specific stimuli. One such receptor is that of the nociceptor, which we alluded to in our previous blog post (see here). The nociceptor is the closest thing to a "pain receptor" we have in our body. The reality though is that it's not a pain receptor at all. In fact, there are no pain receptors in our bodies. Nociceptors, like other receptors, are designed to respond to stimuli. In this case it detects noxious stimulus. The messages a nociceptor sends to the brain provides information regarding tissue damage or potential tissue damage that a stimulus can cause if something doesn't change. This is like a warning to the brain that a 'threat' or 'danger' is present. Keep in mind that we do not feel nociception but rather the brain decides if the 'danger message' is a credible threat or not. If credible, then pain may present.
Interestingly pain isn't the only 'protective' measure used by our brains to protect us. We also may exhibit an altered movement pattern or strategy due to a given 'danger message'. Historically it was believed that once we experience pain we then consequently have a change in our movement; however, now it is believed that pain and altered movement are two of the potential protective actions our brains may use to protect us. In the example presented in our previous post, my brain had a choice to make. Was it more 'dangerous' for me to walk on my busted ankle/foot or was it more 'dangerous' to stay on a vertical face of a mountain side? My brain chose that it was better to get off the vertical face of the mountain and therefore overrode my ankle/foot pain long enough for me to get to safety. The fact of the matter was that my movements back up the mountain, through efferent signaling from my brain, was considerably different than it would have been had I not damaged my ankle. This was an alternative protective measure used by my brain given the bunted pain response during my accent.
Increasing or Decreasing Protection: A matter of modulation...
As we go through life we wire and or rewire neural networks based on a number of inputs. These inputs can be associated with a variety of factors that are not only physical in nature. Recall the biopsychosocial model of patient care? As we mentioned in our previous post, we have at least three broad lifecycle factors that intersect to make up the whole of who we are at any point in time from a biological, psychological, and or societal perspective. This compilation of who we become begins at birth and continues throughout adulthood.
According to the Institute of Medicine of the National Academies (2011) there are several life-cycle factors that may promote an altered pain experience. Once we're born this infusion of influence begins with, for example, our biological sex, parental anxiety, or even our ethnicity. As we move into childhood these influences continue to persist albeit from a slightly different vantage point. At this developmental stage many children begin to experience and come to understand some of life's harsher realities such as a death of a loved one; being a witness to violence; or maybe even suffering from abusive interactions themselves. In our world today, being seperated from a mother or a father for various reasons (e.g., divorce) is also very prevalent; and depending on the circumstances of the situation, it can certainly take a toll on the child and how they view their world.
As these children move into and through their teenage years they experience even greater stressors such as academic expectations as well as learning to navigate those wonderful, and sometimes not so wonderful, peer to peer interactions. Many teenagers begin to enter the workforce in various capacities while at the same time losing social support for various reasons (e.g., friendship issues). Not to mention their transition through puberty. As these teenagers begin adulting the "real world" begins to manifest in ways they've not been accustomed to, such as career and family needs along with the stress of their own personal expectations and fear of failure. A person's level of education upto this point will also impact how they recieve, perceive and respond to stressors.
You see everything discussed above may be considered a neurotag that is either action or modulation in nature. Recall that modulation neurotags are those whose influence is within the brain compared to action neurotags whose influence is beyond the brain. From a pain perspective these neural networks can increase protection or decrease protection. Protection being how the brain attempts to protect us through pain and or altered movement, for example. Take a look at the illustration below. This image was modified and recreated from Figure 2.6 in Moseley GL, Butler DS. Explain Pain Supercharged: The Clinician's Handbook. 2017. Noigroup Publications; Adelaide: Australia: pg 22.
The factors on the left are considered those things that modulate or modify our action neurotags which together flavor our outputs such as a given quality of movement or pain experience. According to Butler and Moseley, modulation neurotags can either be experienced as 'dangers in me' (DIM) or as a 'safety in me' (SIM). 'Dangers in Me' are those experiences we are exposed to that cause an increase in our brains protective output compared to those experiences that result in less of a protective response, SIMs. In the example above notice that a memory, the perception of a social threat or even the ever so innocent yet caring phrase of 'be careful of your back' can all modulate an increase in protection, that is observed or felt as an altered action neurotag that will manifest as pain or an altered movement.
There's more to come, so stay tuned!!
If you stayed with us, kudos to you! You should feel a sense of accomplishment, this is some pretty deep stuff. That being said, even if you stuck around we may have created more questions than answers for you. Please feel free to reach out to us. We'd love to connect and discuss this topic with you. We believe this is extremely important in the managing pain and utilize these principles in our clinical practice daily. In our next post, we'll discuss how this information may relate to your own personal pain experience, and how you can possibly help to improve that experience by "retraining your brain".
References:
Relieving Pain in America: A Blueprint for Transforming Prevention, Care, Education, & Research. 2011. Institute of Medicine of the National Academies.
Moseley GL, Butler DS. Explain Pain Supercharged: The Clinician's Handbook. 2017. Noigroup Publications; Adelaide: Australia
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