Critical Review of The Polyvagal Theory (Chapter 2, by Stephen Porges) with Extrapolations to the PRI Approach
The Postural Restoration Institute approach incorporates the idea that the autonomic nervous system influences asymmetrical patterning of the human body. An imbalance where the sympathetic system is overactive can manifest in the typical neuromuscular patterns (AIC, BC, PEC, TMCC, and/or visual) we encounter. PRI directed interventions aim to neutralize these motor patterns and hence create a three dimensional alternating relationship between them in the human body.
The Polyvagal Theory offers an explanation of the relationship between the sympathetic and parasympathetic systems that can be extrapolated to the PRI approach to facilitate our goals of balanced allostasis in the body. The process of neuroception evaluates risk and threat to the human body unconsciously via afferent information from the senses. The body will then react accordingly and either maintain a parasympathetically dominant state (restorative) or mobilize into a sympathetically dominant state (fight or flight). In extreme cases of stress, another branch of the parasympathetic system will actually override both of these systems to initiate a state of immobilization (freeze).
The Polyvagal Theory describes a hierarchical nature of the sympathetic and two distinct parasympathetic vagal systems that is evolutionarily based. First, there is the most primitive vagal system that can be traced back to reptiles. This system originates in a part of the brainstem called the dorsal motor nucleus of the vagus. This evolutionarily older component of the system is activated in extreme situations of stress and results in massive bradycardia and system shutdown. Historically, this was used successfully by reptiles to feign death and/or conserve resources. However, as mammals evolved they also developed a strong need for oxygen to nourish their more advanced brain and neurological functioning. Therefore, employment of this hypoxic causing emergency system can lead to death in a mammal such as which may be the case in sudden infant death syndrome. The other component of the dorsal motor nucleus of the vagus is involved in regulation of the subdiaphragmatic structures such as the gut as well as branches that connect with the heart. The dorsal motor nucleus origins of the vagus are referred to collectively as the “vegetative vagus” where such vegetative processes are unconsciously controlled as well as being strongly regulated by the hypothalamus.
The next hierarchical level is the sympathetic nervous system which involves mobilization to either a fight or flight state. Activation of this system results in the direct release of catecholamines via sympathetic nerves with coordinated activation of the hypothalamic-pituitary-adrenal axis thereby increasing production of cortisol, epinephrine, and norepinephrine. Physiological effects include increased heart rate and contractility, dilated pupils, bronchiole dilation, heart and brain vasodilation, skeletal muscle vasoconstriction, digestive function inhibition, and increased sudomotor response. Porges also mentions a “synergistic relationship between the sympathetic nervous system and skeletal muscles of the extremities” with the spinal nerves connecting the two systems.
Finally, there is the most evolved and sophisticated level which originates in the nucleus ambiguus located just ventral to the dorsal motor nucleus of the vagus. This is the most recently evolved part of the parasympathetic nervous system and the top of the hierarchy with the prime responsibility of inhibiting the sympathetic nervous system to create a calm state of allostasis. An individual ultimately self regulates through activation of this system. Porges refers to this system as the “smart vagus” with voluntary control characteristics in contrast to the “vegetative vagus” described above.
The nucleus ambiguus (NA) is the origination of not only of the “smart vagus” nerve but the following cranial nerves: facial, trigeminal, accessory, and glossopharyngeal nerves that innervate the face, jaw, neck, larynx, and pharynx. The vagus nerve has neuroanatomical connections with these cranial nerves. These are termed special visceral efferent pathways because they are considered to be under voluntary control yet are also a part of the autonomic nervous system. These nerves are responsible for human behavior such as feeding, sucking, swallowing, turning the head, emotional expression, and communication. The nucleus ambiguus is also home to vagal involuntary general visceral pathways that innervate cardiac smooth muscle and bronchial muscle and thus exhibit influence on the cardiopulmonary system. Just as there is a synergistic relationship between the sympathetic nervous system and somatic muscle function there is a correlation between the general visceral efferents of the vagus and the muscles innervated by the special visceral efferents. One example is that chewing will cause salivation without the presence of food or head rotation will affect cardiac vagal tone. The function of these special visceral efferents allows humans to develop social communication and engagement abilities. However, it is imperative that in order for such social activity and development to occur the sympathetic and reptilian vagal systems must be inhibited by the modern vagal system.
What is important to emphasize in this relationship of systems is that the parasympathetic nervous system’s (ie vagus nerve) primary responsibility is to inhibit the sympathetic system. This has significant correlations to the PRI approach as we are constantly trying to inhibit particular motor patterns representing increased sympathetic activity to achieve neuromuscular balance. In order to help achieve this we would benefit from increased parasympathetic and thus vagal tone.
Due to the anatomical arrangement of the cranial nerves amongst the parasympathetic architecture in the brainstem it is possible to influence one by the other. Due to the shared NA origination with the vagus, stimulation of the facial, trigeminal, glossopharyngeal, and accessory nerves can cause cross-excitation of the vagus. The nucleus ambiguus is also the origin of vagal influence to the pulmonary center and hence a player in the regulation of respiratory rhythm. There is a common cardiorespiratory oscillator that controls the coordination between respiration and heart rate, referred to RSA (respiratory sinus arrhythmia). Heart rate variability is measured as the variation of the time interval between two consecutive cardiac beats thus reflecting functioning of RSA and hence vagal tone. The more variability, the higher the vagal tone. This has significant implications to a PRI practitioner as we are very focused on breathing and incorporate it into practically every technique we do with our patients and clients.
Commentary from a PRI Perspective:
PRI’s TMCC pattern as well as any other over facilitated extension pattern in the body can be inhibited using PRI based exercises. The Supine Active Sacro Spheno Flexion technique is a powerful one that can accomplish this. What is also a characteristic of this technique is that it incorporates jaw movement to the left using the R styloid group to pull the right temporal bone into external rotation. I would like to propose that the extension inhibition not only occurs due to the PRI neuromuscular exercises but in addition to the simultaneous stimulation of the special visceral efferent cranial nerves (trigeminal for left jaw lateral deviation and facial if the lips move too). Clinically, I find that simply by having individuals move their jaw side to side significantly reduces system extension. This could be due to generating alternating movement of the temporal bones but also perhaps from a general system wide vagal influence thus inhibiting sympathetic tone. Furthermore, I notice a correlation between strong descending patterns and poor coordination of the tongue, jaw, as well as the eyes. In these cases, I progressively train the motor control between the jaw, tongue, and eyes in conjunction with PRI exercises to maximize vagal activation and hence parasympathetic tone to ultimately achieve the goal of a creating new neuromuscular patterns in the body functioning in a reciprocal alternating tri-planar fashion.
PRI Vision’s clinical breakdown of the three different levels of vision patients is based off of the extent of one’s integration of retained primitive and postural reflexes. It is hypothesized that when there is excessive energy that goes into coordinating vision and posture there is less energy left over for other processes such as cognitive functioning to smoothly occur. I see a parallel here with the vagus nerve. If the vagus nerve is not functioning properly the system will function under increased sympathetic tone and hence stress. Subsequently, there will be less energy that can be devoted to visual-postural integration. Furthermore, if this stress pattern (decreased vagal tone) is present during development an individual will have less energy to allocate to the crucial visual-motor development that is occurring during these critical time periods of learning. This can potentially explain why we see these various patterns of retained primitive and postural reflexes.
There is a huge PRI correlate between nucleus ambiguus function and the typical L AIC/R BC pattern. In this pattern, we are dealing with a forward head posture that is a result of increased accessory breathing muscle (scalene, sternocleidomastoid, pectoral) activity due to an unopposed left diaphragm leaflet. This posture not only makes it difficult to breath properly but also swallow as the hyoid muscle group becomes over lengthened. Furthermore, this posture creates a retracted mandible which can impact proper jaw functioning. There are also phonation consequences of the L AIC/R BC pattern. As stated previously, the nucleus ambiguus is home to both bronchiole and swallowing regulation centers as well as the trigeminal nerve.
When considering the impaired breathing, swallowing, phonation, and mastication parallels between poor vagus nerve/nucleus ambiguus function and the forward head and hyperinflated posture seen with a L AIC/R BC pattern one must assume there to be a connection. Taking this a step further one can’t help but ask the questions “What came first? Is there another system involved with the development of these patterns?” I believe the answer to be “all of the above.”
First, the development period when these patterns are being created seems to be crucial. Industrialized nations’ modern day children typically are not participating in the same types of activities or environments they did during the majority of our evolutionary history. First, there is overall less physical movement and more sedentary behavior. Second, the activity that does occur is more often done indoors in relatively small familiar spaces vs open, outdoor, novel spaces. Third, the excessive use of two-dimensional and close visual based activity is overwhelmingly prevalent today and was virtually nonexistent for most of our evolutionary history. This combined lack of traditional motor and visual activity and stimuli must have profound implications for the improper integration of primitive reflexes and development of globe on orbit, head on body, body on body, and neck on body relationships.
One must also wonder as to what else can influence the neural activity in this part of the brainstem? The answer to this I believe to be a very complex one and likely involves multiple other systems. However, research is beginning to uncover the connection between our gastrointestinal microbiome and the nervous system, with the vagus nerve as a primary communicator. Not only are we not moving or visually processing our bodies the same as we used to but we are also eating very different foods from our ancestors. Our diets can have a significant impact on the state of our microbiome and as research is showing, our nervous system. Likewise, it is possible that our posture and nervous system functioning can have an impact on the state of our microbiome.
Finally, in any kind of extension pattern, whether it be R TMCC, R BC, Superior T-4, PEC, or L AIC, there will be accompanying tri-planar torsion through the sphenobasilar and C0-2 region near where the brainstem is located. It is plausible that the resulting biomechanical alignment issues at the sphenobasilar and C0-2 complex can facilitate brainstem compression in this area creating a pseudo type Arnold Chiari Malformation. This could potentially influence not only nucleus ambiguus function but additional brainstem activity as well. There is a case study published (“Is Chiari malformation a cause of systemic hypertension and sinus bradycardia? A case report and literature review” by Majid Ghasemi, Khodayar Golabchi, Vahid Shaygannejad, and Majid Rezvani in J Res Med Sci. Jan 2011; 16(1): 115–118) that describes a case where a patient was diagnosed with Arnold Chiari Malformation with symptoms of headaches, sinus bradycardia, and diastolic hypertension. Once she had surgery to correct it these symptoms disappeared. The authors theorized that compression of the rostral part of the ventrolateral medulla oblongata and subsequently tension of dorsal nucleus of the vagus and the nucleus ambiguus were responsible for the clinical presentation. Therefore, it is quite plausible that in other cases of compression to the brainstem one might find additional nucleus ambiguus and dorsal nucleus of the vagus functional difficulties such as those described in this review.
In conclusion, I believe chapter 2 of The Polyvagal Theory by Stephen Porges offers a powerful explanation of the relationships between the parasympathetic and sympathetic nervous systems. These dynamics can potentially be influenced through breathing and special visceral efferent activity to ultimately assist with PRI goals of tri-planar reciprocal alternating movement. Furthermore, there are striking parallels between nucleus ambiguus and vagal function with the impaired functions associated with PRI’s L AIC/R BC/R TMCC pattern. Considering all the potential system influences on these relationships is important in considering intervention strategies.