This important research is best credited to Stephen Porges. It is so important that many others have developed his material and integrated his conclusions into research and training. This includes people like Bessel van der Kolk, Deb Dana, Dan Siegel and Peter Afford.
Why is Porges’ work so important? The ‘flight/fight‘ response has been around for eons. Much was known about how it worked; how it was triggered and led us to recovery (if all went well). What Porges identified, however, was that the simple model of autonomic nervous system (ANS) overlooked some important features. The ANS plainly played a central role in initiating and sustaining the flight/fight response. It seemed as though a ‘pumping’ action kept us in balance.
The ANS, with its sympathetic and para-sympathetic systems, stimulated us and then calmed us down. It got us motivated to act in emergencies, and ensured we recovered afterwards. For a rather complicated, but thorough and insightful illustration into the way the autonomic nervous system works, take a look at Babette Rothschild’s web site.
My understanding is that Porges identified that the Vagus nerve, the longest nerve in our body, was more than a single conduit. This nerve running the length of our upper body and comprised several off-shoots – hence, ‘Polyvagal’. More to the point, he concluded that its ‘parts’ emerged at different times in our evolution. Here is how Porges illustrates this point:
Note that the diagram is covering millions of years and mammals went on to emerge slowly, helped by the hasty departure of the dinosaurs.
There were no human beings around 10’s of millions of years ago. It is likely that mammals only survived by being small and able to live underground – fox-like creatures – living long before mammals rose up and became two-legged.
In particular, there is a ‘reptilian’ element in our lower vagus that promotes immobilisation. This is fine for reptiles, they are not warm-blooded in the way mammals are. Reptiles can stay still for long periods and suddenly spring into action to defend themselves or to attack others.
Humans cannot afford to use that strategy so easily, for so long. To compensate, over time, mammals developed an upper part of their Vagus nerve to minimise any tendency to be immobilised for extended periods.
In time, evolution created a system whereby mammals could be ‘immobilised without fear‘ and without risking fatally low rates of ingestion of oxygen.
That state of affairs – being immobilised without fear – rather assumes that an infant can adopt that strategy in a safe place. For this to happen, an infant needs a caretaker who can be trusted (we are very vulnerable, and much at risk when immobilised).
For more on this important human response, take a look at:
The later evolution of the Vagus nerve played a large part in helping mammals, including human beings, to detect situations in which they were safe. This process was helped by evolution of the lateral Vagus nerve as a ‘social engagement system‘. This helps humans find out who we can do business with.
Through this system, infants learn who could be trusted, and how much they can be trusted. Infants learn very quickly whether to trust or mistrust a carer. However, one sad outcome of this development is that a ‘decision’ to trust, or not, is taken very early on in the infant’s life. The evidence suggests that these ‘decisions’ are made in our first year or two. The available evidence suggests that it is not easy for growing children to revisit that ‘decision’ and make changes to it.
BUT IT IS NOT IMPOSSIBLE, indeed, notions of ‘neuro-plasticity’ suggest that it is feasible to adapt and redesign our neural pathways.
Even so, those decisions cast a long shadow and so we may need to cast our attention back many years when in therapy.