Polyvagal Theory
To appreciate the theory developed by Dr Stephen Porges , a little update on neuro-anatomy will be helpful . Porges has detailed how the neural regulation of the ANS has changed through evolution . In mammals , such as we humans , the ventral ( front ) side of the vagus nerve has evolved to respond to cues of safety in our environment and interactions . This branch of the vagus originates in an area of brain stem known as the nucleus ambiguus . It travels primarily to organs above the diaphragm and interacts within the brain stem with structures regulating the striated muscles of the face and head . This relationship , of vagus nerve to striated muscle fibres associated with expression , is central to appreciating how this branch of the vagus has become known as the social nervous system . It supports feelings of physical and emotional safety and creates emotional connection to others in our social environment . This emergent social engagement system provides the mechanism for co-regulation of physiological state , as mammals can convey cues of safety and danger — via vocalisations , head gestures , and facial expressions — to conspecifics and other species as well ( such as our pets !). To survive and prosper mammals need to be able to consistently and successfully down-regulate primitive defence mechanisms .( 17 )
The dorsal ( back ) side of the vagus nerve responds to cues of danger . We have this branch in common with all vertebrates and it functions to down-regulate the body into a low energy-consuming state of immobility , or freezing . In humans and other mammals , it manifests as feigning death for survival – play dead and they ’ ll leave me alone - and the trauma-driven responses of syncope and dissociation .( 18 )
The brain does not have to consciously evaluate for risk or safety . Porges proposes a new term , neuroception , for the subconscious activity in the brain that monitors the environment and alerts us to either what and whom is unsafe , or to situations that are safe and nurturing . Other authors have reported that the brain can get stuck in a negative bias where the neuroceptors perceive almost every situation and interaction as dangerous , with associated aggression , high anxiety and other forms of emotional distress . Furthermore , in some instances , neuroception appears to switch off almost entirely , leaving the person with an inability to sense real threats to safety .( 17 )
JATMS | Autumn 2023 | 21