Why do perceptions of pain following traumatic or prolonged stress events differ in people?
We were asked why some children who have had many early painful procedures in the NICU as infants appear not to notice pain when they are older.
Our autonomic nervous system responds to stress (pain in this instance) with both sympathetic and parasympathetic activation. Depending on which has been most helpful at the time of significant or prolonged stress, the nervous system lays down a response framework. This drives our future responses to stress.
Looking at the work of Stephen Porges and his Polyvagal Theory may help to understand different long-term responses to pain.
First, Porges outlines that we have two types of parasympathetic responses facilitated by two different branches of the vagus nerve, hence ‘polyvagal’ theory.
- Ventral vagus nerve route – this becomes available to us towards the end of our time in the womb and becomes myelinated over the first year of life. It helps us to be in homeostasis, feel calm and available for social interaction. Its maturation is helped by early feeding, cuddles, skin-to-skin, parentese, parent-child gaze as well as close and attuned interaction of significant others. It enables mild stress to be regulated and resolved by interaction with others.
- Dorsal vagus route – this is the older, unmyelinated parasympathetic response route which harks back to reptilian times. This is functioning early in our development in the womb.
Secondly, Porges suggests that in the event of stressful events we typically have three levels of response.
1st. The Ventral Vagal Parasympathetic response – we look to others for support and we can maintain homeostasis, that is, I feel safe – I’m OK. If this is not sufficient or available e.g. we are too young and this option is not yet functioning (when born prematurely) or we have not experienced nurturing, early parenting and care that supports maturation of this response route, or the stress is too great, then we move to the second option.
2nd option: our sympathetic response kicks in. Our sympathetic response to stress is our ‘flight and fight’ response, producing adrenaline and cortisol. This line of defence engages heightened arousal and movement. We mobilise to resolve the stressful experience.
If mobilisation is not possible e.g. when too young, too incapacitated, restrained in someway, too overwhelmed by the stimuli in the moment, or no one responds to your behavioural cues to help you, we fall to our final, 3rd option.
3rd option: ‘freeze’ response state. This is our dorsal vagus parasympathetic, opioid mediated stress response associated with shut down and dissociative states. Opioids act as an analgesic, blunting the negative affective component of pain. Here we are also helped to reduce the attention assigned towards the incoming painful stimuli, reducing our response to it.
When we are born very early we only have stress response options 2 & 3 available to us.
In the longer term if the sympathetic responses are more embedded within us, we are more likely to be anxious and hypersensitive to stimuli, including pain. This is where we see ‘tactile defensiveness’ and hypervigilance.
If our dorsal vagus parasympathetic response is more embedded, then we become hyporesponsive to painful stimuli. We do not give it the level of attention and response typical in others who have not undergone these experiences. We appear hyporesponsive to painful experiences, brush it off and may appear to be attending elsewhere, not attending to the painful event.
At Sensory Babies we feel this fits with our clinical observations, but other explanations may emerge.