Section 4: Integrated Autonomic System Understanding & Behavioral Adaptation
Before the work of Walter Hess, it was assumed that the central nervous system was not involved in the management of the autonomic nervous system – a reasonable conclusion given that John Langley’s work clearly demonstrated the autonomic nervous system could function independently. In 1949, Hess determined that while Langley’s interpretation was not wrong, it was not complete. Hess demonstrated unequivocally that stimulation of specific areas within the brain influenced autonomic nervous system responses through his experiments on the diencephalon and the hypothalamus in particular.
Stephen Porges built upon Hess’s concept of an integrated autonomic nervous system in developing a more comprehensive understanding of how the neural circuitry within the autonomic nervous system operates. His Polyvagal Theory, first published in 1994, describes how multiple branches of the vagus nerve operate to control different aspects the autonomic nervous system. The role of the vagus nerve in moderating heart rate was well known prior to 1994, but Porges demonstrated that parasympathetic action of the vagus nerve is due to a phylogenetically newer myelinated branch. He further identified an older, unmyelinated branch of the vagus nerve that triggers the “freeze” response as a separate and distinctly different neural action than the well-known fight/flight response, which is controlled by the sympathetic nervous system (see Cannon). Porges also discovered that in addition to moderating heart rate, the myelinated vagus also links the heart to the facial muscles and head to influence facial expression and social engagement. The Polyvagal Theory, therefore, identifies a social component of the parasympathetic nervous system. Porges’s research allowed him to further define how mammals respond to danger and delineated three distinct behavioral strategies engaged by humans to ensure survival in safe environments:
- Social Engagement & Communication
• Engages the social systems and maintains homeostasis
• Promotes restoration and growth, ensures long-term survival
• Managed by the parasympathetic system, controlled by the phylogenetically youngest myelinated vagus
• Engages the fight/flight response
• The body’s first line of defense, ensures near-term survival
• Managed by the sympathetic system, controlled by phylogenetically older sympathetic adrenal circuit
• Engages the freeze response
• Body’s final line of defense, ensures immediate survival
• Controlled by the phylogenetically oldest un-myelinated vagus circuit
The Polyvagal Theory adds to the integrated model of the nervous system by incorporating a social dimension to the sympathetic nervous system and identifying a phylogenetically older circuit that activates the freeze response. Porges has added to the existing model of how vertebrate mammals, and humans in particular, respond to life situations, an important finding for the development of clinical application and highly consistent with the neurosensorimotor reflex integration approach of the Masgutova Method.
Below are more in depth summaries of the contributions made by: