Polyvagal theory

Polyvagal theory is a medical hypothesis related to the central nervous system’s (CNS) influence over the autonomic nervous system (ANS) and how the ANS adapts to these influences in various scenarios. Developed by Dr. Stephen Porges in 1994, the theory focuses on the role of the vagus nerve as it relates sensory awareness and response. Polyvagal theory offers a new perspective that connects ANS function to behavior and examines how neural circuitry regulates the autonomic state. It also interprets how the autonomic nervous system adapts as part of its evolutionary development. The theory challenges conventional understandings of nervous system function. It also encourages a more integrative approach to the examination of the role neural mechanisms play in biobehavioral regulation.

Background

The nervous system is a complex network of nerves and specialized cells called neurons that send electrochemical signals across different parts of the body. These signals determine voluntary and involuntary responses in the body. The nervous system is divided into the central nervous system and the peripheral nervous system. The central nervous system comprises the brain and spinal cord as well as the nerves attached. The CNS is considered the command center of the nervous system and sends signals from the brain and spinal cord to other parts of the body. The peripheral nervous system consists of sensory neurons, neuron clusters, and other nerves that connect the rest of the body, such as the arms, hands, legs, and feet, to the CNS. The peripheral nervous system is further divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system is the voluntary component of the peripheral nervous system while the autonomic nervous system is the involuntary component.

The ANS regulates processes such as breathing, digestion, and blood pressure, which do not require conscious effort. It also plays a role in responding to social cues that may pose a danger. In this regard, the ANS is further divided into two other branches: the sympathetic system and the parasympathetic system. Each branch regulates specific involuntary bodily reactions to danger such as the flight-or-fight response, eye pupil dilation and constriction, and heart beat rate.

The autonomic nervous system contains a number of nerves that all serve different functions. The longest nerve in the autonomic nervous system is the vagus nerve, which extends in two sections from the brain stem down through the neck and into the chest and abdomen. It is one of the most important nerves in the body, carrying both motor and sensory information and providing nerve function to multiple organs. It helps regulate heart rate, blood pressure, digestions, sweating, speech, and other functions. Due to its varied role, the vagus nerve has been of keen interest to researchers in regard to its potential use in medical therapy. Vagus nerve stimulation has been studied as a treatment for a variety of medical issues such as peptic ulcer disease, epilepsy, and depression. Researchers have also examined electrical vagus nerve stimulation as a possible treatment for conditions such as hypertension, migraines, tinnitus, fibromyalgia, and weight loss.

Overview

Polyvagal theory examines the relationship between vagus nerve function—and autonomic mechanisms in general—and visceral experiences. First proposed in 1994 by Dr. Stephen Porges, director of the Brain-Body Center at the University of Illinois at Chicago, polyvagal theory suggests that sensory signals that are sent to the brain rather than sent away from the brain are interconnected with and sensitive to the autonomic nervous system. The theory posits that people’s facial expressions, tones of voice, bodily movement, and other social cues impact physical responses within the body. Porges points to evidence based in evolutionary biology and neurology to support the theory.

From the day a human is born, its brain learns to distinguish between danger and safety. A baby learns to feel safe in the arms of a parent while it learns to feel unsafe around strangers, loud noises, and other discomforts. Porges describes the process by which the nervous system scans for danger in the environment as neuroception. He defines neuroception as an involuntary mechanism within the autonomic nervous system, the center of social cue response learning. The vagus nerve plays a critical role in this process. During neuroception, both sides of the vagus nerve are stimulated yet respond in distinct ways. The front, or ventral, side of the nerve responds to social cues associated with safety, while the back, or dorsal, side responds to social cues of danger. The front nerve makes people feel safe and connected, while the back nerve disconnects people from a feeling of safety and puts the body into a state of self-protection.

With this in mind, polyvagal theory suggests that rather than there being a balance between the sympathetic and parasympathetic parts of the ANS, there is actually a hierarchy of inbuilt responses that have evolved over time. The first and oldest pathway is the immobilization response, which involves the body becoming immobile when faced with extreme feelings of fear and danger. The next oldest pathway is the mobilization pathway, which involves the sympathetic nervous system springing into action as adrenaline kicks in and the body mobilizes against danger. The newest of pathways, social engagement, responds to cues of comfort and safety. It is this pathway that allows people feel connected and engaged.

Polyvagal theory suggests people are able to move in and out of these pathways as the situation calls for. Trauma plays a major role in the development of this hierarchy. People who have experienced extreme trauma may have a distorted ability to scan an environment for danger. The body’s defense system kicks into overdrive, causing people to read cues as dangerous that are not so. The opposite can also occur in those who have not experienced trauma, with individuals reading a situation as safe when it is in fact dangerous. The polyvagal theory has been both praised and criticized for its viewpoint of the autonomic nervous system as it relates to behavior and psychology. Supporters note the potential to build upon the theory in research settings, while critics downplay the theory due to its lack of empirical evidence.

Bibliography

Cherry, Kendra. “What Is the Autonomic Nervous System?” VeryWell Mind, 3 Feb. 2020, www.verywellmind.com/what-is-the-autonomic-nervous-system-2794823. Accessed 12 Mar. 2020.

Clarke, Jodi. “Polyvagal Theory and How It Relates to Social Cues.” VeryWell Mind, 5 Aug. 2019, www.verywellmind.com/polyvagal-theory-4588049. Accessed 12 Mar. 2020.

Fogoros, Richard N. “Anatomy of the Vagus Nerve.” VeryWell Health, 21 Oct. 2019, www.verywellhealth.com/vagus-nerve-anatomy-1746123. Accessed 12 Mar. 2020.

“The Polyvagal Perspective.” Biological Psychology, vol. 74, no. 2, 2008, pp. 116–143.

“The Polyvagal Theory: New Insights into Adaptive Reactions of the Autonomic Nervous System.” Cleveland Clinic Journal of Medicine, vol. 76, no. 2, 2009, pp 86–90.

Seladi-Schulman, Jill. “What Is the Vagus Nerve?” Healthline, 31 July 2018, www.healthline.com/human-body-maps/vagus-nerve. Accessed 12 Mar. 2020.

“Stephen Porges Bio.” Stephen Porges Official Web Site, www.stephenporges.com/bio#. Accessed 12 Mar. 2020.

Zimmermann, Kim Ann. “Nervous System: Facts, Function & Diseases.” LiveScience, 14 Feb. 2018, www.livescience.com/22665-nervous-system.html. Accessed 12 Mar. 2020.