User:Jtwsaddress42/Projects/Project 5/Chapters/Chapter 2

Stephen W. Porges - The Polyvagal Theory

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In the mid 1990s, Stephen W. Porges developed his Polyvagal Theory. The work of Porges on the phyletic origins of the autonomic nervous system and its CNS nuclei in the brainstem adds an additional layer of nuance to Romer's picture of vertebrate organization with respect to mammals. Porges postulates that the neuroanatomical basis of a social-engagement system was constructed out of a recently remodeled and myelinated-pharyngeal arch system and its brainstem nuclei, a newly emergent neocortex with inhibitory outflow, and the myelinated division of the parasympathetic nervous system. Porges envisages a social-engagement system of neural architecture constructed out of the remnants of the pharyngeal arch system as amniotes adapted to land, switched modes of breathing; and, ultimately in mammals, and closed the cardiopulmonary loop reestablishing fully-oxygenated bloodflow required for endothermy and optimum utilization of the metabolic oxidative potential. Every 10 degrees Celsius the temperature rises, the metabolic rate doubles. Once the metabolic resources were available, the sympathetic nervous system was "revved-up" and constantly idling with an inhibitory "brake" on it. This allowed the transition from a stimulus-induced behavior typical of cold blooded organisms with limited metabolic resources - where the autonomic nervous system operates with a threshold response to engage, activation, peak execution, and a decay back to baseline to recharge resources; to a pattern or real-time behavioral foraging and ecological exploration that is made possible by the increase in available metabolic resources that allows the sympathetic to remain in a state of high output, but is tamped down by inhibitory myelinated parasympathetic and cortical outflow. The basic picture is one where the anatomy of the social-engagement system is riding on top of a metabolically revved-up subcortical and sympathetic nervous system - and, acting as an inhibitory and modulatory brake on the lower systems. The social-engagement component of the system are related to the way that the gill arch cartilages, muscles, and nerves are remodeled into larynx and the vocalization apparatus, the ear and the auditory-orienting system within the newly emergent head-neck system, and the muscles of the head and neck. The auditory system of mammals is tuned to the species-specific frequencies of their larynx and vocalization apparatus. The system evolves the capacity for social-engagement through reciprocal co-engagement between members of the same species as they become cognitively and behaviorally entrained via vocalization and posturing. Edelman describes the neuroanatomy of the somatic division, the central nervous system (CNS), as organized into a structure that is made up of nerve tracts as well as nuclear, laminar and columnar cell populations - and in contact with the external world via the primary sensory sheets and muscle ensembles. Since Edelman focuses primarily on the operation of the neocortex, his hedonic feedback systems emanate from the world of subcortical structures that have roots deep in the brainstem and connections to the visceral body via the autonomic nervous system. Communication between the two divisions can occur via the autonomic, endocrine, and immune systems but, the key neural integration point is where the reticular network of the brainstem ties together the autonomic and cranial nuclei of the pharyngeal arch system, the general and special tracts of the peripheral nervous system, and the global neurotransmitter fountains that diffusely project upward to the midbrain, thalamus, and cortex, as well as back down the spinal column. This is the link between somatic and visceral divisions that allows the visceral nervous system to act as a mechanism of selection in the recruitment of neuronal groups whose configurations are adapative such that the hedonic needs of the visceral body are being met.

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