Polyvagal Theory

The Polyvagal theory (gr. 'polus', “‘many’” + 'vagal', ''vagus nerve'') specifies two functionally distinct branches of the vagus, or tenth cranial nerve. It serves to identify the relationship between visceral experiences and the vagus nerve's parasympathetic control of the heart, lungs, and digestive tract. The theory was introduced in 1994 by Dr. Stephen Porges, director of the Brain-Body Center at the University of Illinois at Chicago. According to the theory and its increasing evidence base, the autonomic nervous system is interconnected with and sensitive to influences that flow from the body toward the brain, called afferent influences. This effect has been observed and demonstrated by adaptive reactivity dependent on the neural circuits' phylogenetical development. It builds on the study of what Charles Darwin referred to as the “pneumogastric nerve.' The polyvagal theory claims that humans have physical reactions, such as cardiac and digestive changes, associated with their facial expressions. Porges argues this theory with observations from both evolutionary biology and neurology.The vagus nerve is a primary component of the autonomic nervous system. Polyvagal theory outlines the structure and function of the two distinct branches of the vagus, both of which originate in the medulla. More specifically, each branch is associated with a different adaptive behavioural strategy, both of which are inhibitory in nature via the parasympathetic nervous system. The vagal system is in opposition to the sympathetic-adrenal system, which is involved in mobilization behaviours. According to polyvagal theory, these opposing systems are phylogenetically arranged.In order to maintain homeostasis, the central nervous system responds constantly, via neural feedback, to environmental cues. Stressful events disrupt the rhythmic structure of autonomic states, and subsequently, behaviors. Since the vagus plays such an integral role in the peripheral nervous system via regulation of heart rate, it follows that the amplitude of respiratory sinus arrhythmia (RSA) is a good index of parasympathetic nervous system activity via the cardiac vagus. That is, RSA is a measurable, noninvasive way to see how the vagus modulates heart rate activity in response to stress. This method is useful to measure individual differences in stress reactivity.As described by Bessel van der Kolk, professor of psychiatry at the Boston University School of Medicine: .mw-parser-output .templatequote{overflow:hidden;margin:1em 0;padding:0 40px}.mw-parser-output .templatequote .templatequotecite{line-height:1.5em;text-align:left;padding-left:1.6em;margin-top:0}The Polyvagal Theory provided us with a more sophisticated understanding of the biology of safety and danger, one based on the subtle interplay between the visceral experiences of our own bodies and the voices and faces of the people around us. It explains why a kind face or a soothing tone of voice can dramatically alter the way we feel. It clarifies why knowing that we are seen and heard by the important people in our lives can make us feel calm and safe, and why being ignored or dismissed can precipitate rage reactions or mental collapse. It helped us understand why attuning with another person can shift us out of disorganized and fearful states. In short, Porges’s theory makes us look beyond the effects of fight or flight and put social relationships front and centre in our understanding of trauma. It also suggested new approaches to healing that focus on strengthening the body’s system for regulating arousal.