The Pocket Guide to the Polyvagal Theory by Stephen W. Porges

Author:Stephen W. Porges
Language: eng
Format: epub
Publisher: W. W. Norton & Company
Published: 2017-10-26T16:00:00+00:00

THE VAGUS NERVE: A FAMILY OF NEURAL PATHWAYS

Dr. Buczynski: Let’s get to a couple more foundational questions before we move on. Biologically, I know, the vagus nerve is not just one nerve, but a family of neural pathways originating in several areas of the brainstem and going into several branches of the vagus.

Dr. Porges: The vagus is a cranial nerve that emerges from the brainstem. We have 12 cranial nerves, and some of these cranial nerves control the striated muscles of the face. In general, when neural control of muscles is discussed, the discussion focuses on skeletal muscles involved in moving the limbs of our body that are controlled by nerves emerging from the spinal cord. But cranial nerves are not the equivalent of spinal nerves regulating the striated muscles of the face and head. For example, facial expressivity is regulated by cranial nerves emerging from the brain and is distinct from the spinal regulation of the muscles of the trunk and limbs. In addition, the vagus is involved with the regulation of the striated muscles of the face and head, and it also regulates smooth and cardiac muscle.

Polyvagal Theory focuses on five cranial nerves that emerge from the brainstem. We can describe the brain as an inverted triangle with the expansive cortex at the top and a narrow brainstem at the base. Most research studying the brain, especially with imaging techniques, focuses on the cortex and tends to minimize and neglect the brainstem. However, from a parsimonious perspective, the brainstem is a final common pathway through which most information comes into the brain and leaves the brain. It is useful to think of the brainstem as a building block upon which other processes are scaffolded. If we can’t regulate our physiological state, which is a brainstem responsibility, then we have difficulties accessing and processing higher cognitive functions.

The brainstem as an anatomical structure provides an opportunity to compare across vertebrate species and to infer the adaptive modifications that occurred during evolution. Functionally, the brainstem is the major regulator of physiological state. Since the regulation of physiological state prepares us for a range of behaviors, the brainstem is critical in all aspects of our behavior as well as in the maintenance of homeostatic processes that keep us alive and healthy.

A major clinical issue manifested across diagnostic categories is difficulty in behavioral state regulation. Polyvagal Theory assumes that difficulties in behavioral state regulation are manifestations of difficulties in autonomic regulation. The ability to regulate behavioral state is a clinically relevant process when discussing borderline, schizophrenia, depression, anxiety, autism, and other clinical disorders. The ability to regulate state, when context and demands dynamically change, is frequently used to operationalize resilience.

To understand the relevance of the Polyvagal Theory to clinical conditions, it is necessary to think of the vagus as a bidirectional conduit connecting the brain with the body. The vagal conduit has motor pathways going from the brain to the organs and sensory pathways coming from the organs to the brain. Polyvagal Theory is about the brain–body communication that involves the vagus.

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