The vagus nerve in paediatric practice (for allied health practitioners)

The vagus nerve is the largest cranial nerve in the body, and many of us probably remember being taught about how it controls the autonomic nervous system. Heart rate, blood pressure, breathing rate and speed of peristalsis, to name a few. And while these functions are definitely vagal, they account for only 10-20% of total vagal function. 

The vagal system has two branches - dorsal and ventral. The dorsal vagal system is what develops first in utero, and is the slowest part of the vagus nerve. It is often associated with the ‘freeze’ response in adults, and has links to the fear paralysis reflex in infants. Next to devleop in utero is the sympathetic nervous system, which often coincides with baby’s movements being felt by mother. And the final portion of the vagus nerve to develop is the ventral vagal branch. The ventral vagus is the ‘fast’ branch of the vagus, and its myelination takes place from in-utero through to approximately 18 months of age (some research indicates even longer). 

The vagus nerve influences the sense of safety felt by an infant, child and adult alike. However, how each age range expresses their feelings of safety or threat can be very different. In a developing infant brain, it is thought it develops in conjunction with the right hemisphere to enable social engagement - such as smiling at caregivers, coo-ing, and making eye contact. The things babies to do be oh-so-cute and create a sense of safety, in a time when they’re physically vulnerable!

The vagus, being inhibitory, often pulls us out of the stress response. As an example, a child feels unsafe (for whatever reason), their sympathetic nervous system activates (and so it should), and then the vagus is what inhibits the sympathetic response to recalibrate to a calm baseline. This can happen daily, and we are supposed to be able to dip in and out of sympathetic activation, BUT we are supposed to be able to recalibrate after. 

Research indicates that mothers who experience high levels of stress during pregnancy tend to have babies who show higher signs of stress at 12 weeks of age, relative to low-stress pregnancies. Which is something a lot of us would see in our practice - “highly strung” mothers creating “high needs” babies, and maybe even struggling to connect with their baby (because their own social engagement system is downregulated). This can also be referred to as low vagal tone (in both mother and child, in this example).

Firstly, a baby has lower vagal capacity than an adult, and as a result will require much more coregulation (and signs of safety). This coregulation might come from the primary caregiver, but also their general environment, and also their own internal environment (eg. the gut microbiome). The more a caregiver responds to a baby, the more it reinforces a sense of safety in the baby. 

And this is all good and well, but what if the baby enters the world with low vagal tone? Many babies who enter our practices are typically more irritable than average, and perhaps aren’t sleeping or feeding well. They potentially have lowered vagal tone (and are at higher risk for irritability). Well then we are working with an altered baseline - with sympathetic overactivation, and lowered ability of the vagus to activate the parasympathetic system. And how many of us have heard a mother say they do “all the things for coregulation”, but their baby is just so unsettled?!

Babies with low vagal tone tend to sleep less, need more connection from mother, are often described as “koala babies” who need to be held all the time, or don’t want to be with anyone except their primary caregiver. They may have difficulty with breastfeeding (due to altered swallow), they may have a head tilt that doesn’t resolve with adjusting, and they may also appear to retain a startle, or be easily set off by noise/people, because their sympathetics are no longer being inhibited. 

Older children who have low vagal tone tend to be nervous in new situations (maybe even freezing in space), continue to want coregulation to fall asleep/stay asleep, have difficulty with social connections (within age expectations), and possibly even digestive issues. They tend to be emotionally volatile, dysregulated over small things, and unable to regulate themselves once they’ve been triggered. When you look at all these behaviours from our primary need to feel safe, it is clear that when a child doesn’t have the vagal capacity to feel safe, they need more safety cues from their caregivers and environment. 

It is worth mentioning mothers too, because our children mirror us, which is particularly important if a mother has low vagal tone and cannot regulate her own nervous system (let alone coregulate with her child). If you see both mothers and their children in the clinic, considering their dynamic feeding off each other is imperative for care. 

Assessing vagal tone in babies, children and adults requires a combination of history and examination findings. If you haven’t started considering the power of the vagus nerve in your patients, and their results, now is the time! 

The Vagus Nerve in Paediatric Practice is a yearly program, teaching allied health professionals how to view their patients with a vagus nerve lens, to improve their clinical outcomes.

References -
[ Rash, J., Campbell, T., Letourneau, N., Giesbrecht, G.F. (2015). Maternal cortisol during pregnancy is related to infant cardiac vagal control. Psychoneuroendocrinology,54(April), 78–89. http://hdl.handle.net/1880/51005 ]

[ Sachis PN, Armstrong DL, Becker LE, Bryan AC. Myelination of the human vagus nerve from 24 weeks postconceptional age to adolescence. J Neuropathol Exp Neurol. 1982 Jul;41(4):466-72. doi: 10.1097/00005072-198207000-00009. PMID: 7086467. ]

[ Kim HG, Cheon EJ, Bai DS, Lee YH, Koo BH. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature. Psychiatry Investig. 2018 Mar;15(3):235-245. doi: 10.30773/pi.2017.08.17. Epub 2018 Feb 28. PMID: 29486547; PMCID: PMC5900369. ]