We are all aware of the five major senses that help us process and understand our environment and our sense of self: Taste, Smell, Touch, Sight, and Hearing. While these come as second nature, they are actually complex neural pathways that help us to process large amounts of stimuli and information. All of this information is processed in the central nervous system (brain & spinal cord) where we are then able to comprehend the world around us. These senses can be bundled into a category called “exteroception”, or stimuli that come from external surroundings. But, our senses go way beyond just external stimuli. Our central and peripheral nervous systems (CNS and PNS) work in concert to help us interpret internal stimuli as well. These senses can be broken down into what’s called “proprioception” and “interoception”. How do internal stimuli help you? It allows you to understand things such as:
- where your body is in space
- how hard to push a door to open it
- regulates our body temperature
- alerts you to tension or tightness
- organ function
All of this sensory information coming in from the peripheral nervous system is integrated into the central nervous system and used to paint a portrait of ourselves and how we view ourselves in our environment, or our “body representation”.  Our sense of self.
How Does This Relate to My Chronic Pain?
With the advances in neuroimaging technology, we are better able to understand how sensory inputs affect and are processed by the brain and central nervous system. More evidence surfaces each day that individuals with chronic pain have differences in the processing of sensory information compared to those who do not suffer from chronic pain. Many of those who have chronic pain know that pain is not always associated with some sort of pathology in the affected body part. For example, many with chronic low back pain have had x-rays or MRIs that have come back negative or with no evident pathology. Yet, the individual continues to report low back pain. So where is this sensation of pain coming from? We mentioned earlier how critical the CNS and processing of information in the brain is to how we perceive ourselves. There is growing evidence to suggest that it is during the integration processes in the CNS that errors occur. To better explain how chronic pain and sensory perception are related we will break down the portions mentioned earlier: Proprioception, Exteroception, and Interoception.
Proprioception: Do You Know Where Your Body is in Space?
Proprioception is the understanding of where one’s body is in space and feeling the amount of tension or force being produced. The test that is often used to test this proprioception is with eyes closed having someone move an individual’s extremity either up or down. This is often done with the first, or great, toe. The individual cannot see, hear, taste, smell or touch anything that tells them where their toe is. They use the input and sensation of proprioception to know in which direction the toe, or any other limb, is facing.
There is a difference between how individuals with chronic pain and those without are able to process this information. Individuals with chronic pain scored lower when asked to reproduce a posture or limb position of the unaffected side without the use of visual input . You may also note a difference in the ability for those with chronic pain to detect movement of the affected limb or body part. In this study, researchers measured the minimum threshold needed to detect movement of a limb or body part. They found that those with chronic pain were less sensitive to movement when compared to an unaffected body part and when compared to individuals without chronic pain . To the same point, there has also been evidence that shows when normal joint function is restored, improvements were noted in both position and movement sense of the affected limb .
Muscle Tightness? Force Production and Tension
Another facet of proprioception is the perception of force production and muscle tension. Various studies have been conducted on individuals with chronic tension headaches as well as chronic pain in the shoulders, neck, and jaw. They show that there is increased muscle tension found in the painful region using EMG studies, and can be alleviated with the use of biofeedback and training. The big takeaway is that the individuals with chronic pain were not able to sense that increased muscle tension was the cause of their pain. This can indicate that they have damped awareness or feedback from the involved musculature that is causing their pain .
Pain has also been indicated in the limiting of force production from a painful area. When researchers measured the amount of force produced by individuals with chronic back pain vs those who had no pain they found that the two groups did not vary much in how much force they produced. However, the chronic back pain group took significantly longer to reach their peak force production and interestingly enough reported less pain during force production. This lead researchers to infer that the chronic pain patients had unknowingly developed compensatory muscle recruitment to avoid activating the painful musculature. This again points to higher sensory processing differences between those with pain versus those without .
Posture Reflects a State of Mind – Posture and Balance
Lastly, proprioceptive feedback has a large role in an individual’s posture. There have been many studies and reviews done that have all had a similar result: Those with chronic pain (low back pain being the greatest studied) demonstrate increased postural sway in quiet standing than those without chronic pain. All of the studies were down without any experimental perturbation. The question that has arisen from these studies is the mechanism by which the occurs .
Some studies affirm that the reason for the postural sway is due to altered sensory feedback or, more specifically, a re-weighting of sensory input. Sensory input from the painful area is not taken into account, or weighted, as heavily as other inputs such as vision or feedback from a non-painful area. This idea coincides with those we have discussed earlier when vision was removed from individuals with chronic pain, they demonstrated a greater inability to correctly determine the position of their painful limb or body part .
Other studies attest that the increase in postural sway is due to changes in motor patterns or postural strategies. EMG data show that the activation of postural and stabilizing musculature such as the transversus abdominus and external oblique are delayed in individuals with chronic back pain. This evidence would agree with the studies mentioned earlier in which force production was achieved via altered activation patterns compared to those without chronic pain 
A Quick Summary
Chronic pain can affect proprioception. In other words, it interferes with your awareness of your own body! This partially explains why those with chronic pain have challenges with a new exercise or why certain exercises (balance) can be very difficult. There is no one singular reason as to why or how chronic pain alters sensory integration. As illustrated above there are many components of sensory integration that are abnormal and likely play a role in the changes that take place. However, with greater advancements in technology and a greater understanding of the true physiological changes that manifest themselves as what we call “chronic pain”, further studies and treatments are able to be developed to treat and relieve chronic pain.
The Big Take Away – 7 Ways You Can Improve Proprioception
Here are ways to improve proprioception. Most of these are fun and help pain in many ways.
- Balance training and exercise
- Tai Chi
- Qi Gong
- Agility and coordination activities
- Sports and athletics
- Progressively difficult activities of daily living
Thank you all for reading, in Part 2 of this discussion we will dive further into exteroreception and interorecpetion and how they are related to chronic pain.