The brain, movement and pain! Part two.
In the first part of this 3 part series we looked at patterns and how the brain recognizes patterns of information to then be able to recall or auto-associate a response from stored memory.
This is our model of
In this second part we are going to look at perception and the systems that send this sensory information and how it is centrally processed. We compare the stored pattern with the sensory pattern flowing into the brain to then be able to make a prediction on the likely outcome of executing the stored pattern. The cerebellum is vital to this process. One of its major roles is matching the senses with the stored patterns and help executing and adjusting the associated motor programs. Our perception helps us to compare the stored pattern with the actual situation that is occurring.
The sensory information includes muscle length and tension, joint position, pressure, vibration and temperature and pain signals. We also receive sensory information from the visual and vestibular systems.
We refer to it as perception rather than information because the way that we perceive this information wildly differs from one person to the next. In fact the same person can perceive this information differently one hour to the next. A signal that may cause pain when you feel tired and sensitive may not bother you when rested and strong. This is because this information is centrally processed and modulated by our 'neuromatrix' as we first discussed in part one of the blog. Our energy levels, stress levels, health, and emotional state affect this modulation. You name it and it will affect your central processing of information.
Our sensory pathways are recursive meaning the higher centers in the brain modify and shape the incoming flow of sensory information. Our perception of the world is shaped by us internally as well as us externally. Much the same as the information we read is shaped by our political and moral beliefs. Two people can interpret the same information differently based on their internal modulation. Perception is not a direct record of the world around us but a subjective interpretation. German philosopher Kant referred to these brain properties as 'a priori' knowledge.
“The brain responds to the perceived, not the actual reality”
Moseley and Flor 2012
Our main sensory sources of information from the body are the ascending somatosensory pathways that flow up the spinal cord into the cerebellum and Cerebral cortex.
We have signals that transmit information to conscious and subconscious areas of the brain. The higher sensory cortex receives conscious information that needs to be taken notice of such as an itch we need to scratch and pain (also projected to the insular and cingulate cortexes)
The cerebellum receives subconscious information that allows us to move effectively without the need for conscious thought.
These sensory pathways from the body include:
The Dorsal column medial leminiscus pathway or DCML transmits conscious proprioceptive information such as touch from the body up into the sensory cortex via thalamus.
The spinocerebellar tracts four divisions transmit subconscious proprioceptive information from the body up into the cerebellum.
The anteriolateral Spinothalamic tract transmits temperature and pain information to the thalamus and then higher up to various cortical areas.
The cerebellum is an amazing area that comprises 10% of brain size but contains over 50% of the total neurons. This alone tells you its importance.
The Cerebellum matches intended movement or patterns with sensory information to help create a prediction of the outcome and then relays this information to the brain stem and motor cortex. In this way it is able to react to the variations in patterns through the sensory systems and vital to the model of patterns, perception and prediction in the brain.
The Cerebellum compares internal feedback information that reports intended movement with external information that reports the actual motion. It is constantly integrating information from various senses, comparing them to stored patterns and helping us adjust to perform a task. It is essential in executing coordinated motor control tasks both in terms of planning and modification during execution. It is in communication (via thalamus) with the higher brain structures of the cerebral cortex that allow it to compare our movement with and then adapt many of the stored patterns. The constant loop of sensory and motor information between the cortex and cerebellum is vital for our movement success.
The cerebellum is divided into 3 functional divisions:
Vestibulocerebellum – Regulates balance and eye movements
Receives input from visual cortex and vestibular nuclei.
Helps with important reflexes such as the vestibulo ocular reflex . The vestibulo ocular reflex is characterized by compensatory eye movement induced by head movements. As the head is generally constantly moving along with the movement of the body, this reflex is particularly important.
Spinocerebellum – Body and limb movements
Receives information mainly from somatosensory receptors via spinal cord
The cerebellum actually learns patterns to be able to provide feed forward motor control to regulate motion. This anticipatory ability (even in before sensory feedback occurs) allows smooth and accurate motion to occur. This must be a learnt behavior assigned to a motor pattern as we build a vocabulary of movement and based on previous sensory feedback rather than instantaneous feedback.
Cerebrocerebellum – Movement planning.
Receives information from cerebral cortex via pontine neclei of the pons.
The cerebrocerebellum is involved in high-level internal feedback circuit dealing with motor planning and regulating cortical motor patterns.
To understand our clients/patients movement we also have to understand how the different sensory pathways influence the execution of our movement.
This has to include the visual and vestibular systems as well as the proprioceptive as they play a major role in the sensory matching within the cerebellum. We will discuss later in the blog the implications of sensory mismatch. All of our senses including smell and hearing will have implications for movement as they help us form a representation of the world around us.
The sensory system does display a hierarchy of importance with the visual system often biasing information from others sources. In essence that means the stretch and strengthen model of affecting tissue maybe redundant in the face of higher dysfunctions within the sensory system hierarchy. ‘Stretching out’ a muscle such as a tight pectoral may be futile. Massage, needling, releasing and manipulation as well. The muscles postural state/position that is dominated by an ocular imbalance will prevail in the long term until it is rectified. Up to 70% of postural control comes from the eyes and motor pattern and visual information are integrated within the brain.
Such things are not controlled at a ‘local’ level of bone, joint or muscle movement. The anticipatory cerebella activity influencing muscles at a local level to maintain a predominant posture may be too strong to overcome without addressing the sensory cause at a higher level.
Ocular weaknesses and lack of control that affects our field of vision or eye dominance will directly limit our ability to move. The brain suppresses information from the weaker or less dominant eye (unless short sighted, go figure?) leading to a reduced field of vision and a dominant head, body posture and movement patterns to accommodate the stronger eye. This suppression can happen if the images from each eye don't match, one is blurry for example, the brain may choose to suppress the information from it. Changes at a muscular level will not change this postural motor program within the brain that is dominated by the eyes. A shift in approach maybe needed with long term postural problems that do not respond to localized (muscle level) treatment. This can also create intra system sensory mismatch. Sensory mismatch is something we will discuss later in the blog.
Much of our so-called proprioceptive training is really visual, vestibular and proprioceptive as we are probably using the first two systems for balance and stability. We tend not to look at the visual and vestibular system when we look at movement dysfunction or ‘stability’ however.
Any of our sensory systems will impact on our movement potential in terms of muscular length and force that are controlled by brain based motor patterns.
Our assessment and treatment instead focuses on localized and contrived muscle activation in non functional positions (prone) that does not take into account the pattern recall, perception and prediction model of the brains role in movement and pain.
In fact over time sensory information can alter the way we move. Rather than remaining physiologically set, as was the prevalent understanding of the brain, the brain is a plastic and changeable area, both in terms of physical structure and functional organization.
As we learn and experience new things the brain is able to make new neural connections and strengthen existing ones involved within a new physical skill or even non physically such as learning a new language.
This follows the “neurons that fire together wire together” principle from the first part of this blog. The neurons involved in the new patterns strengthen their connections plastically changing the functional organization of the brain.
This also helps us understand the neurological principle of “use it or lose it” or “neurons that fire apart, wire apart”
Connections or patterns that we don’t use, well simply, we lose or are eroded! That’s why when you perform a skill you have not performed for a while; you probably will not be as good at it as when you are regularly practicing.
"Axon branches more active in releasing neurotransmitters persist at specific neuromuscular sites, whereas less active axon branches retract, resulting in the canonical elimination of polyneuronal innervation"
Jackie Yuanyaun Hau et al.
Simply put less active axon branches die off and more active ones persist and grow stronger. In this way we refine our neural capability for efficiency and therefore increased survival and performance potential. This process is modulated by what we do on a daily basis.
This has huge implications for movement and posture. If we do not use certain movements of the body then we will get worse at using them in the future. The neural connections and associated patterns with these movements diminish or are overtaken by stronger patterns.
A good example would be a flat foot. The neurons associated with the motor pattern of creating an arch within the foot will not be as strongly connected as they would with a foot that regularly creates an arch and has neurons that fire together to create this reaction. In this case it would be move it or lose it!
So the neural hardware required to run this particular software or movement program is not as strong as it should be. Simply applying a software/movement pattern to the hardware without trying to upgrade the hardware may mean the movement will not run as smoothly as you desire. Simple feedback based exercises or manipulations may not address the hardware issues associated with creating neuro plastic change.
In fact cortical changes have been shown to be stronger when associated with learning about the experience and not just the sensory feedback involved. Cortical representations can increase two to threefold within 1-2 days of the new sensory motor skill being first acquired (Merzenich and Blake 2002-2006)
The process of changing the hardware maybe a far more concentrated, cognitive and directed approach than subconsciously driven exercise, stretching or hands on techniques. The change of a long held postural or movement pattern can be a challenging process that requires a level of cognitive engagement. To to break the predominant pattern you have to be aware enough not to slip back into it!
Within our cerebral cortex we have cortical representations of areas of our body. This cortical representation is a network of neurons that can be in many areas of the brain and is associated is with an area of the body. The most famously understood is in the somatosensory/motor areas.
So for the foot we have a foot area and for the hand a hand area! Sensory information from the body is projected to the area that it is associated with. Dr Penfield way back in the 1930’s described these areas as the Homunculus or little man when he first mapped the cortical areas.
A famous study by Merzernich in 1984 mapped a monkey’s hand before amputating the third finger and then mapping the brain again 62 days later.
He found that the second and fourth finger had invaded the area formally associated with the third finger. A case of use it or lose it!
This has huge implications for conditions such as phantom limb pain as explored by the great neuroscientist Ramashandran. Even though the body part has been amputated the cortical representation of the body part remains. Adjacent areas that are somatopically-organized invade this remaining area. This means the wrist representation is next to the forearm, forearm next to elbow etc. So the arm representation that remains, even though it has physically been amputated below the elbow, is receiving sensory feedback from the elbow that has invaded the cortical space formerly occupied by the arms sensory feedback!
Flor et al (1997) found with chronic low back pain patients, the cortical back representation in the somatosensory cortex (S1) had invaded the lower leg representation and the extent of this expansion was closely associated with the chronicity of the pain.
This sensory change also has implications for our ability to move. Our sensory information flows through our sensory areas before going to our motor areas. In this way what we are sensing directly affects the way we move. Equally the way we move affects our sensory areas. This again can be a case of move it or lose it.
Thomas Hanna coined the phrase 'Sensory motor amnesia' A condition in which we lose the ability to voluntarily move certain parts of our body in the ways that we want to. Often they stay 'stuck' in an unchanging posture either unable to relax or contract and create change in our postural position. This can come about through habitual movements and postural positions and persistent protective motor patterns after an injury. The associated neural pathways to change the posture or move these parts of our body will fade with inactivity.
“Without constant and accurate feedback from our touch maps, our motor maps can’t do their job. And so a feedback loop of mutual degradation is set up: Your touch map worsens so your motor map worsens, which worsens your touch map more”
The body has a mind of its own. Sandra and Matthew Blakeslee.
Both David Butler and Dr Cobb of Z health have cited this blurring or smudging of the map as a cause of, or as a result of pain. The brain can perceive the inaccurate map as a ‘threat’ to the system as reduced map clarity will have an impact in cases of sensory mismatching.
This remodeling also happens in the face of pain. Previous injury and pain therefore affects future movement through neuroplasticity. Australian neuroscientist Lorimer Moseley has been researching the sensory cortex changes in chronic pain patients and how this affects motor control.
"One aspect of the changes that occur when pain persists is that the proprioceptive representation of the painful body part in primary sensory cortex changes. This may have implications for motor control because these representations are the maps that the brain uses to plan and execute movement. If the map of a body part becomes inaccurate, then motor control may be compromised – it is known that experimental disruption of cortical proprioceptive maps disrupts motor planning"
Lorimer Moseley, Professor of Clinical Neurosciences and Chair in Physiotherapy, School of Health Sciences, University of South Australia.
The implications of this are important because we all pick up injuries both minor and major in our lifetime that will erode and remodel our movement ability at a cortical level. Rehabilitation from injury generally involves getting rid of the pain response and not restoring any movement deficits or neuroplastic changes associated with the injury. This can lead to chronic injury/pain situations. Localized protective motor patterns originally induced during a pain response may persist even though pain has ceased. This can also alter gross movement patterns and affect other areas within a function related kinetic chain.
Sensory motor mismatch has also been attributed to pain. We can relate this back to the input mechanisms in the cerebellum discussed earlier. McCabe (2005) examined Ramashandran’s (1995) informal implication of pain in the absence of tissue damage being caused by incongruence between motor intention and proprioceptive feedback. A mirror was used to disrupt motor command and proprioceptive feedback in this study. Surely this would also involve the visual system, which must be taken into consideration when discussing sensory and motor congruency and looking at the cerebellar inputs and outputs.
Dr Cobb from Z health also discusses sensory mismatching as a cause of threat and pain to the body. For example if we have an eye dominance that creates a tilted and rotated head position it maybe that the visual system information is now at odds with the vestibular information when integrated in the cerebellum. The head position assumed to be in neutral from the visual system is not in vestibular neutral (because the head is tilted) The information from each source is conflicting. This can lead to inter sensory mismatching and a 'threatened' state in the brain.
“it remains possible that in a sensitized or disrupted neurological system such as in neuropathic pain, sensory-motor incongruence might contribute to, or maintain, pain”
Moseley and Flor 2012
Pain is a complex subject however, not just linked to proprioceptive or nociceptive feedback. There are many brain-based reasons for pain beyond the scope of this fairly simple blog and many other areas of the brain to explore in relation to pain. (disclaimer over!) One such reason is the apparent threat of damage to bodily tissues without input from nociceptive fibres.
In the next part we will look at the prediction the brain makes based on the stored pattern and the perception of sensory information it receives. This prediction may result in pain even in the absence of any tissue damage. In this way the body can predict a threat to the tissue even in situations when it may not be warranted. We will also look at the central sensitization of the processing of sensory information. Signals that may not have previously exceeded the threshold for threat or pain will can be interpreted as thus as the central threshold decreases.
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