A core functionality of biological organisms is to track regularities in the environment and utilize those regularities as a substrate for predictions. In general, organisms that can identify markers of risk, danger, and safety and respond appropriately to those markers are better adapted than organisms that lack this functionality. Thus, the largely reflexive fight-flight-freeze responses to percieved danger are near universally distributed features that species possess. On the opposite side of the ledger, an externally safe environment requires a matching physiology that not only inhibits the flight-flight-freeze reflex but also a neurophysiology that promotes repair and growth. The psychologist Stephen Porges coined the term neuroception to describe this functionality of matching neurophysiological states to features in the environment. Risk appraisal and the matching neurophysiological state – neuroception – occurs largely outside our conscious awareness and is mediated by the vagus nerve.
The vagus nerve is known as the tenth of the twelve cranial nerves. It emerges from or converges into nuclei in medulla. Etymologically, the word, vagus, means wanderer and speaks to the fact that the vagus nerve distributes its motor and sensory, efferent and afferent fibers, throughout the body. However, in reality, the vagus nerve is not a single nerve but is broadly composed of three neural circuits (polyvagal) mediating distinct adaptive functions related to neuroception. The first circuit – immobilization – that we share with reptiles mediates the freeze or death feigning response that serves to conserve oxygen in the face of threats. We freeze when avoiding detection is the best strategy. The second circuit – mobilization – promotes the fight or flight response of the sympathetic nervous system by serving analogously to a brake release. When the environment is perceived as dangerous, the brake is released resulting in increased heart rate and activation of the adrenaline and cortisol mediated stress response of the HPA axis. The evolutionary most recent third vagal circuit – social communication – promotes prosocial behaviors, fosters calm behavioral states, and inhibits the defensive fight-flight-freeze responses of the first and second circuits.
Thus, when the environment is perceived as safe, the fight-flight-freeze response is inhibited and also social interactions and engagement are promoted. A familiar face, a reassuring tone of voice, rhythms of speech are all markers of safe environments and have the capacity to restore physiological equilibrium and promote growth and restoration. Therefore, in a vicious feedback loop, as long as people feel threatened they cannot meaningfully engage with others and if they cannot meaningfully engage with others they continue to perceive the environment as dangerous. There is not only intrinsic variability to the default thresholds of neuroceptive systems but these systems are continuously tuned from life experiences. Systems in persistently threatening environments or without reassuring social bonds will be tuned to be over-sensitive to perceived threats resulting in mismatches in the environment and neurophysiological states. Over time, these over-sensitive systems lead to persistently activated HPA axis, chronically elevated cortisol levels, and the sequelae of neuropsychiatric and cardiometabolic diseases.
It has been widely established that social determinants of health account for a large proportion of variation in health care outcomes. This is unsurprising considering the fundamental nature of humans as social animals. We depend on social networks to distribute risk, share loads, and regulate neurophysiology in such a profound way that it might be beneficial to expand the concept of the self to include the network. Inadequate or disrupted networks result in maladaptive physiologies contributing to the epidemic of chronic diseases that have been largely resistant from, episodic and individual centered medical care that is the paradigm of our medical system. If the above thesis is true, then in order to make a positive impact on the epidemic of socially mediated chronic diseases, the expanded self must be better quantified (next essay) and interventions should be tailored and designed for this quantified expanded self.