In order to sustain life, the body has two complementary nervous systems: a Sympathetic (arousing) and a Parasympathetic (calming). Both are needed not only for psychological balance, but for survival. Without a Parasympathetic modification, the heart would beat too quickly to sustain life.
The Parasympathetic takes over in relaxation, sleep, meditation, massage, gentle touch, connecting deeply with another person, nurturing – both nurturer and nurtured.
When stress is very great, the Sympathetic system automatically goes to a fight or flight response. This is built in to the system. It can happen in response to external threat or the perception of threat.
Either fighting or fleeing can resolve the stress.
If neither is possible or successful, the sympathetic arousal can get so extreme that it is too much for the body to handle.
At this point, we have a failsafe survival mechanism. The Parasympathetic system spikes. It comes in so strongly that it overwhelms the Sympathic arousal and sends the person into a state of Freeze. This can be full collapse, dissociation, or a more partial freeze such as inability to think clearly or access words or emotions, or move parts of the body.
This can be momentary, short term – such as a possum freezing and becoming reanimated after the predator leaves, or, in humans, continue indefinitely.
The Vagus vein has two branches: dorsal (back) and ventral (front). The Dorsal Vagus is a large, primitive nerve, which is common to all animals, including fish. It goes down the spine and has a role in controlling our lungs, hearts (moderating heartbeats so they don’t get too rapid) and stomach (where it actually aids digestion).
Normally, the Dorsal Vagus serves a very positive function. It helps the body gently pendulate between arousal and relaxation. However, when the Sympathetic is too aroused, the Dorsal Vagas nerve can shut down the entire system and we go into freeze. This is most common in trauma and shame, including developmental trauma.
The Ventral or front Vagus Nerve is common to mammals, which raise live young. It goes directly to the muscles of the face and helps determine expression, and is active in social engagement. Social engagement for mammals is a way of activating the Parasympathetic system. Thus, according to experts in the field of the connection between emotions and the physical body (Dr Stephen Porges, Dr Peter Levine, Dr Bessel Van Der Kolk), social engagement – or attachment behavior – is a way to prevent and come out of Dorsal Vagal Shutdown.
Following on from this theory, it’s important for people who’ve experienced trauma to have and maintain contact with people who express emotions such as engagement, concern, understanding and compassion.