We can frame three essential principles on how the nervous system works that are relevant to cranial work:
One: Essential reflexes can highjack the functioning of the whole body.
The most important reflexes to understand are
- Flexor withdrawal (the response when we step on a pebble, it involves the whole of the spinal cord and interferes with control of the whole musculoskeletal system)
- Sympathetic overactivation (fight, flight, flooding)
- Parasympathetic overactivation (freeze, dissociation)
These reflexes are discussed more fully in Sumner and Haines 2010. It is very hard to function effectively if we are contracting away from an irritant, stressed/ unsafe or not present.
Two: Evolutionarily newer functions inhibit older functions.
‘The three circuits are organized and respond to challenges in a phylogenetically determined hierarchy consistent with the Jacksonian principle of dissolution. Jackson proposed that in the brain, higher (ie, phylogenetically newer) neural circuits inhibit lower (ie, phylogenetically older) neural circuits and ‘‘when the higher are suddenly rendered functionless, the lower rise in activity.’’’ Porges 2009 (1) (N.B The three circuits referred to are communication, mobilisation and immobilisation)
The social nervous system is engaged first as part a hierarchy of responses if we are threatened.
The polyvagal theory of Stephen Porges (2003, 2009) develops the basic trauma model and lists a hierarchy of responses, each involving progressively older evolutionary responses of the autonomic nervous system: communication (social nervous system), mobilization (sympathetic nervous system) and freezing (parasympathetic nervous system). In humans the first responses are about communication and orientation. According to the principle of Jacksonian dissolution (see the quote above) the newer social nervous system inhibits the stress response of the sympathetic nervous system. In turn mobilisation inhibits freeze.
Initially, with any perceived threat there is an communication or orienting response, an engagement with our environment to gain more information. In the orienting response, the person locates and assesses the source of the threat. There may then be a communication, for example, using negotiation or social skills to address the threat. In this stage a mouse may sense a hint of cat and sharpen its hearing and smell, open and move its eyes and turn its head to gain more information. There is a temporary stilling of the heart, breathing and posture. In humans this orienting response is highly developed and frequently includes communication. This is based on our previous experiences of attachment to figures of safety, we can sooth and reassure ourselves in contact with others.
The social nervous system links together cranial nerves V, VII, IX, X and XI. They control sucking, swallowing, voice, breathing, middle ear muscles, heart rate, ingesting, facial expression and head movements. This response comes from a newer part of what was classically considered part of the parasympathetic nervous system (2). A big part of the social nervous system involves signals along the ‘new vagus’, a mylinated (therefore quicker) tract controlled by the nucleus ambiguus (3). Porges contrasts this with the old unmylienated vagus which is controlled by the dorsal motor nucleus and iniates the freeze response.
Upright posture is also a relatively new function.
Communication and social interaction are considered drivers for increasing brain size and complexity (Attenborough 2002). Standing upright, via our unique human upright posture, is also considered an evolutionary selective pressure on increasing brain size (4). It takes a lot of neurology to overcome gravity and balance and walk on two feet. It is relatively new neurology. Porges makes the case that the phylogenetically newer neural circuits of communication inhibit older stress response. I would argue that the same could be said of the parts of the nervous system that deal gravity and movement. When we open our heart, lift our chest, expose our more vulnerable front as we stand upright and walk freely we become more human.
Three: We can ‘reboot’ the nervous system. Improving afferent input will improve the functioning of the whole nervous system.
‘Approximately 80% of the vagal fibres are afferent and provide important information regarding the visceral state.’ ‘The central regulator of the vagus in the brainstem is both an input and an output of other feedback systems; the vagal system becomes a component of a more integrated neural feedback system and a portal to neural systems in other areas of the brain.’ ‘There is a strong neuroanatomical and neurophysiological justification to predict that stimulation of the vagal afferents would change activity of higher brain structures.‘ Porges (2003) (Bold added)
The section highlighted in bold in the Porges quote above is the really hopeful part for bodyworkers. If we can stimulate any single afferent to the brain stem and limbic system we will improve the activity in the whole nervous system. An example from the work of Porges of this principle in action:
The Listening Project.
The Listening Project is ongoing research with children diagnosed with autism. It is led by Stephen Porges (Porges 2008) and uses the Polyvagal Theory as the theoretical basis. The research uses an intervention that provides acoustic stimulation to children during a free-play condition. The intervention has shown promising results in enhancing social interaction and communication behaviors. This is quite incredible research. By challenging the middle ear muscles, and improving the associated neurological control, Porges has demonstrated improvements in the ability of the whole individual.
‘The model is an optimistic model, because it assumes that for many children with social behavior and communication difficulties the Social Engagement System is neuroanatomically and neurophysiologically intact. The problem is conceptualized as a functional deficit. Thus, to obtain the desired behavior, our task is to stimulate the cortical regulation of the brainstem system that regulates the muscles of the head. The theory predicts that once the cortical regulation of this brainstem system is engaged, social behavior and communication will spontaneously occur as the natural emergent properties this biological system.’ Porges 2008
Understanding the above three principles generates treatment strategies.
Improve information flow.
Any inputs that improve our ability to orient and communicate will inhibit the stress response. One of the most powerful ways of doing this is to offer stillness, space and allow the system to orient to resources and the environment in present time. The extra information from the whole body and the whole field will allow contextualisation of cycling and speedy stories and slow down the stress response. The quick response to the question ‘Am I Safe?’ is meditated by centres deep in the brain. Simply, we can talk of the limbic system and the brain stem controlling dissociation and activation. These deep brain centres receive information from three sources; from the cortex down; from the external senses in; and from the body coming up. The figure above attempts to show this flow of information (5).
If we are overwhelmed, wherever the information comes from, the amygdala will trigger communication, mobilisation or freezing (Porges 2003). Orienting to the flow of information from the inside of body (interoception) and awareness of the body in space (exteroception) are much more powerful ways of inhibiting the cascade of the stress response than using the cortex down route. It is very hard to think your way out of anxiety, it is much easier to orient and feel your way out. Biodynamic cranial work can use these pathways from the body and the environment to help the system come into present time.
Apply the Vagal Brake.
Porges describes the vagal system as a feedback system consisting of motor pathways to change visceral state, sensory pathways to monitor visceral state and brain structures to evaluate the sensory input and to regulate the motor output. The vagus nerve especially acts to inhibit the sympathetic nervous system. The sympathetics are set to run in overdrive all the time, health depends on an active vagal brake. Thayer and Lane (2000) show that ANS imbalance (causing anxiety, poor attention and immune disorders as shown by proinflammatory cytokines plus other conditions) is due to low vagal tone.
The vagal brake not working causes the sympathetics to be dis-inhibited and the system to become much less flexible in its responses. The interoceptive signals from the organs and internal environment, especially the heart and gut, utilising the heart brain and belly brain, are very powerful tools in inhibiting the sympathetics. They are also essential to our sense of self and our experience of emotion and pain (Craig 2003).
Switch on the extensor muscles.
In overwhelm the sympathetics and flexor muscles are switched on and the extensor muscles are inhibited (6). The flexor muscles are the muscles that we would use, all over our body, to grab hold of a telegraph pole. The extensors allow us to come into a softer, upright, open and receptive posture. Supporting this posture and the reflexes to maintain it can be a useful tool in clinic work. Often in clinic work asking people to feel the back of their body on the table can help engage the extensors. Any movement information (especially spinal joints) provides afferent input (sensory information) to the nervous system that improves the functioning of the whole body and brain.
All animals that evolved to move show strong symmetry around a midline. Supporting balance around the midline is a powerful way of stimulating the neurological control of movement.
Stimulate social nervous system sensory pathways.
The social nervous system nerves listed by Porges are cranial nerves V (trigeminal), VII (facial), IX (glossopharangeal), X (vagus), XI (spinal accessory). The motor outputs of the social nervous system according to Porges are head turning, muscles of facial expression, muscles of mastication, middle ear muscles, larynx and pharynx, heart and bronchi. The sensory inputs to the social nervous system cranial nerves are interoception (discussed above), sound (the input that changes the tension in middle ear muscles), mucusol linings of the oral cavity, nasal cavity, and sinuses, the teeth, and the sutures, dura, skin and arteries of the cranium (Barral and Croibier 2009 p.13).
For craniosacral therapists the ability to interact with the dura and sutures of the skull is central to the cranial paradigm.
‘The cranial dura mater possesses a rich and vast sensory innervation.’ Barral and Croibier 2009 p.25
The trigeminal nerve carries most of the sensory information from the dura back to the brain stem. The sensory ganglion of the trigeminal nerve is huge, indicating its importance. Theoretically, therefore, resolving inertia in the dura should offer a burst of afferentation to the social nervous system. (The other big sensory input to the trigeminal ganglion is from the teeth and the periodontal ligaments holding the teeth in place.)
If Porges can switch on the whole nervous system of autistic children by stimulating cranial nerve control of the middle ear muscles, it is hard not to be excited about the possibilities in cranial work of stimulating other social nervous system cranial nerves. Particularly the trigeminal nerve via the dura and teeth and the vagus nerve via interoception. Any interventions that support the functioning of the cranial nerves (e.g. opening of the jugular foramen, opening of the sinuses, free movement of the bones of the cranial base, nerve and blood flow through the carotid sheath, orienting to the ganglions of the cranial nerves) potentially have the ability to ‘reboot’ the whole nervous system.
1 The part in double quotes is a direct quote from Jackson. The reference given is: Jackson JH. Evolution and dissolution of the nervous system. In: Taylor J, ed. Selected Writings of John Hughlings Jackson. London: Stapes Press; 1958:45–118.
2 Thanks to John Chitty for pointing out that the new vagus model and the social nervous system are not described by Porges as being part of the parasympathetic nervous system. In Cranial Intelligence I did not fully understand this and was imprecise in saying parasympathetics inhibit sympathetics – what I should have said is the social nervous system and/or the vagal brake inhibits the sympathetics.
3 Porges contrast this with the old, unmylienated vagus. Freezing relies on unmyelinated vagal efferents originating in the dorsal motor nucleus of cranial nerve X (DMNX) (Porges 2003). The DNMX projects to the heart and bronchi, drastically slowing down the heart and respiration.
4 Jared Diamond (2005) p260 describes becoming upright as a significant jump in human evolution, accelerating development: ‘The first (jump), occurring between 100,000 an 50,000 years ago, probably was made possible by genetic changes in our bodies: namely by evolution of the modern anatomy permitting modern speech or modern brain function or both.’
5 The labelling on this diagram has been updated from the version in Cranial Intelligence (Sumner and Haines 2010). I have since read Craig (2003) and Blakeslee and Blakeslee (2007). I like their framing of interoception versus exteroception and moved proprioception to the label outside in/ awareness of the body in space.
6 Ida Rolf quoted by Lyons 2010: ‘She said that if there is no psychology, there is only perverted physiology. Dr. Rolf believed that all negative emotion is expressed through the shortening of the extensors’
ReferencesAttenborough, D. (2002) Life of Mammals. DVD from the BBC. Barral, J.P., and Croibier, A. (2009) Manual Therapy for the Cranial Nerves. London: Churchill Livingstone, Elsevier. Blakeslee, S. and Blakeslee, M. (2007) The Body Has a Mind of Its Own. How Body Maps in Your Brain Help You Do (Almost) Everything Better. New York: Random House. Craig A.D., (2003) Interoception: the sense of the physiological condition of the body. Current Opinion in Neurobiology 2003, 13:500–505 http://www.current-opinion.com Diamond, J. (2005) Guns, Germs and Steel – A Short History of Everybody for the Last 13,000 Years. London: Vintage Books. Lyons, J. (2010) Dr Rolf – “What is Structural Integration?”. Retrieved October 6, 2010, from http://ezinearticles.com/?Dr-Rolf---What-is-Structural-Integration?&id=4821627 Porges, S. (2003) The Polyvagal Theory: phylogenetic contributions to social behavior, Elsevier Science 2003 Porges, S. (2008) The Listening Project. http://www.education.umd.edu/EDHD/faculty2/Porges/tlp/ retrieved 1st Oct 2010. Porges, S. (2009) The polyvagal theory: New insights into adaptive reactions of the autonomic nervous system. Cleveland Clinic Journal of Medicine Vol 76, Supplement 2, April 2009. Sumner, G. and Haines, S. (2010) Cranial Intelligence – A Practical Guide to Biodynamic Craniosacral Therapy. London: Singing Dragon. Thayer J. and Lane R. (2000) A model of neurovisceral integration in emotion regulation and dysregulation Journal of Affective Disorders 61 ( 2000) 201 – 216