If you're a parent of a child with autism spectrum disorder (ASD) or ADHD, you've probably heard a lot about the brain. About neurotransmitters, about genetics, about executive function and dopamine pathways. What you may not have heard much about, despite a rapidly growing body of research, is the vagus nerve.

This is starting to change. Over the past decade, researchers have been building a compelling case that the vagus nerve and the autonomic nervous system are central players in both conditions. Not peripheral factors, but core neurological mechanisms that deserve serious attention. This post is a summary of where that research currently stands and what it means in practice.

A quick summary of what the vagus nerve does

The vagus nerve is the longest cranial nerve in the body, running from the brainstem down through the neck, chest, and abdomen. It is the primary nerve of the parasympathetic nervous system (the "rest, digest, and connect" branch) and carries information in both directions between the brain and virtually every major organ.

Its functions include regulating heart rate, digestion, inflammation, respiratory rate and the social engagement system. This last function is particularly relevant to what follows.

Vagal tone (the level of activity in the vagus nerve) is most commonly measured using heart rate variability (HRV): the natural variation in time between heartbeats. Higher HRV reflects stronger parasympathetic activity and is associated with better emotional regulation, social engagement, cognitive flexibility, and stress resilience. Lower HRV signals autonomic imbalance - a nervous system that is stuck in sympathetic dominance, running hot and unable to shift into recovery and regulation.

Polyvagal theory is all about how the vagus nerve creates safety in the system - whether that be from internal or external environments. The more safety your system can perceive, the more the vagus nerve can engage to shut down the stress response and move into regulation. Of course, it’s not as black and white as “vagus on, stress off'“ - it’s actually quite a complex dance between the body and nervous system.

With that foundation in place, let's look at the evidence.

The vagus nerve and autism spectrum disorder

Autonomic dysregulation is a core feature of ASD

For many years, the autonomic nervous system was considered a peripheral concern in autism — something that might explain some secondary symptoms (gut issues, sleep problems, sensitivity to stimulation) but wasn't central to the diagnosis itself.

That view is shifting. A growing body of research is positioning autonomic dysregulation, and specifically vagal dysfunction, as a core neurobiological feature of ASD, not a side effect of it.

Studies have consistently found that children with ASD show significantly lower HRV compared to neurotypical peers. Meaning reduced parasympathetic activity and a nervous system that leans chronically toward sympathetic activation. A 2020 meta-analysis published in Neuroscience & Biobehavioral Reviews confirmed this pattern across multiple studies, finding that lower HRV is a common factor of ASD. They suggested it could be a ‘potential biomarker’ for ASD [though once you understand the complexity of the vagus nerve, I don’t think this is particularly useful - ie low HRV does not equal autism!!].

What does this mean clinically? A nervous system with low vagal tone and chronic sympathetic dominance is a nervous system that perceives the world as threatening even when it isn't. For a child with autism, this may manifest as heightened sensory sensitivity, difficulty with social engagement, emotional dysregulation, meltdowns, rigidity, and gut dysfunction - all of which are mediated by the autonomic nervous system.

Respiratory sinus arrhythmia and social development

One of the most significant pieces of research in this area comes from a study led by Dr Stephen Sheinkopf of Brown University, which found that the development of respiratory sinus arrhythmia (RSA) - the natural fluctuation in heart rate with breathing, which is controlled by the vagus nerve - is delayed in autistic children. RSA appears to be slow to develop in autistic children at around the same time as the condition's core social traits emerge.

This is not a trivial finding. RSA is one of the most direct measures of vagal tone we have, and it is also bidirectionally linked to social engagement. Polyvagal theory, developed by Dr Stephen Porges, proposes that the ventral vagal complex governs the social engagement system = the capacity to make eye contact, read facial expressions, modulate voice tone, and feel safe in the presence of others.

When the ventral vagal system is not functioning optimally, social engagement becomes genuinely neurologically difficult. Not a matter of choice or preference, but a function of the autonomic nervous system's state. This offers a profoundly important reframe for understanding the social differences seen in autism.

We know that for autistic individuals, having a sense of safety is very important for regulation. And while it can be harder to access, when you get it right, it can make all the difference for that child or adult.

Sensory processing and vagal tone

Research has also found an association between vagal tone and sensory processing differences in ASD. A study published in Research in Autism Spectrum Disorders found that children with ASD showed reduced variability in parasympathetic nerve activity in response to different sensory stimuli - meaning their nervous system was less able to modulate its response to incoming sensory information. Hello sensory overwhelm?!

This offers a neurophysiological explanation for why sensory input can be so overwhelming for autistic children. A nervous system with low vagal tone cannot effectively regulate its own arousal in response to sensory experiences. The result is a sensory experience that is more intense, less filtered, and harder to recover from.

Vagus nerve stimulation (VNS) research in autism

The most direct evidence for the vagus nerve's role in autism comes from research on vagus nerve stimulation — both implanted (invasive) VNS and non-invasive transcutaneous auricular VNS (taVNS), which stimulates the vagus nerve via the ear.

A 2017 paper published in Frontiers in Neuroscience by Jin and Kong proposed transcutaneous vagus nerve stimulation as a promising approach for ASD, based on the vagus nerve's role in regulating the social engagement system and inflammatory pathways that are dysregulated in the condition.

Since then, multiple clinical trials have been initiated. A 2023 study published in Frontiers in Psychiatry examined the feasibility of remotely supervised, at-home taVNS delivery for children with ASD, finding the approach both feasible and showing initial positive signals for core autism behaviours. A 2024 randomised controlled trial protocol published in Frontiers in Psychiatry examined taVNS effects specifically in children with high-functioning ASD, targeting social communication and behaviour through modulation of brain network connectivity.

A trial registered in 2025 (NCT06473623) is currently investigating non-invasive auricular fibre VNS (afVNS) for ASD as a home-based therapy, with outcomes including core autistic traits, gut function, sleep, and autonomic nervous system markers — reflecting the growing recognition that vagal support in ASD needs to address the whole autonomic picture, not just behaviour.

A 2025 review published in Frontiers in Neuroscience by Gargus and colleagues examined the mechanisms of vagus nerve stimulation for neurodevelopmental disorders, with a particular focus on microglia and neuroinflammation — highlighting that VNS may exert some of its benefits in ASD through anti-inflammatory pathways, given the well-documented role of neuroinflammation in the condition.

I certainly love focusing on establishing higher vagal tone in my clinic patients, including many neurodivergent children and adults.

What this means beyond electrical stimulation

It's important to note that the research on VNS devices — while exciting — is not the only relevant evidence here. The neurophysiological rationale that underpins VNS research applies equally to any intervention that increases vagal tone: breathwork, humming, chanting, cold water exposure, safe social connection, rhythmic movement, and chiropractic care targeting the upper cervical spine (given the anatomical proximity of C1 and C2 to the jugular foramen through which the vagus nerve exits the skull).

The question is not only whether electrical stimulation of the vagus nerve helps autistic children — the research increasingly suggests it does — but why. And the answer points toward a framework in which supporting vagal tone, by any evidence-informed means, may have meaningful neurological benefits for children with ASD.

The Vagus Nerve and ADHD

The norepinephrine connection

ADHD is well established as a condition involving dysregulation of the prefrontal cortex (PFC) — specifically, abnormalities in the dopamine and norepinephrine (NE) pathways that underpin attention, impulse control, and executive function. This is, in fact, the neurological mechanism by which stimulant medications work; by increasing dopamine and norepinephrine availability in the PFC.

What is less well known is that the vagus nerve directly modulates the norepinephrine pathway, and this creates a compelling neurological case for vagal support in ADHD.

The vagus nerve, when stimulated, activates a pathway from the nucleus tractus solitarius (NTS) in the brainstem to the locus coeruleus (LC) — the brain's primary norepinephrine production centre — which then projects to the prefrontal cortex. A 2024 review published in Frontiers in Neuroscience by Zhi and colleagues specifically examined this taVNS-NTS-LC-NE pathway in the context of ADHD, proposing that transcutaneous auricular vagus nerve stimulation may offer a non-pharmacological approach to ADHD by modulating the very norepinephrine pathway that is dysregulated in the condition.

In plain language: stimulating the vagus nerve may help regulate the same brain chemistry that ADHD medications target - through a different, non-pharmacological route. You could even try both at the same time and see how your child / yourself responds!

HRV, Vagal tone, and ADHD

As with ASD, reduced heart rate variability [reflecting lower vagal tone] has been consistently documented in children with ADHD. A 2022 paper in Frontiers in Endocrinology reviewing therapeutic applications of taVNS for paediatric disorders noted the evidence linking autonomic dysregulation to ADHD symptomatology and highlighted taVNS as a promising intervention.

The clinical implications of reduced vagal tone in ADHD are significant. A nervous system with low parasympathetic activity is a nervous system that cannot easily downregulate arousal, sustain attention, or recover from stress. The child who "can't sit still," who struggles to transition between tasks, who is easily overwhelmed by sensory input or emotional demands - these presentations are consistent with a nervous system that is running in sympathetic overdrive without adequate parasympathetic counterbalance.

VNS Research in ADHD

Clinical research on VNS for ADHD, while earlier in development than the ASD literature, is showing promising signals.

The 2024 Zhi et al. review in Frontiers in Neuroscience provided a detailed theoretical and mechanistic framework for taVNS in ADHD, noting that previous studies have shown taVNS exerts therapeutic effects on attention, cognition, arousal, perception, and behavioural regulation through the NTS-LC-NE pathway — exactly the pathway that is implicated in ADHD pathophysiology.

Neurostimulation research more broadly has found promising results for ADHD, with a 2019 review in Psychiatria Danubina by Wong and Zaman concluding that neurostimulation approaches show real potential for ADHD management. As taVNS technology becomes more accessible and non-invasive, it is likely to attract increasing research attention in this population.

The gut-brain axis and ADHD

One aspect of the vagus nerve's role in ADHD that is increasingly attracting research interest is the gut-brain axis. The vagus nerve is the primary communication pathway between the gut and the brain, and there is growing evidence that gut microbiome dysbiosis [which is commonly found in children with ADHD] may contribute to ADHD symptomatology through impaired vagal signalling.

This creates a bidirectional therapeutic target: supporting vagal tone may improve gut-brain communication, and supporting gut health may improve vagal signalling to the brain. In clinical practice, addressing both simultaneously as part of a systems-based approach to ADHD, is increasingly well-supported by the evidence.

What does this mean in practice?

The research in both ASD and ADHD is pointing in a consistent direction: the vagus nerve and the autonomic nervous system are not peripheral factors in these conditions. They are central to how they are expressed, and potentially to how they can be supported.

This does not mean the vagus nerve is the only factor, or that vagal support is a cure. Both ASD and ADHD are complex, multifactorial conditions that deserve comprehensive, individualised approaches.

What it does mean is that any approach to neurodevelopmental conditions that ignores the autonomic nervous system is leaving a significant piece of the puzzle on the table.

In clinical practice, supporting vagal tone in children with ASD and ADHD can involve a range of approaches:

Breathwork — slow, diaphragmatic breathing with extended exhale, which is one of the most direct and accessible vagal stimulation tools available, and which children can learn and practice themselves

Humming, singing, and chanting — which directly activate the vagal branches innervating the muscles of the throat and soft palate

Safe social connection and co-regulation — which activates the ventral vagal system; the calm, regulated nervous system of a caregiver genuinely down-regulates the dysregulated nervous system of a child

Rhythmic, whole-body movement — which stimulates the vestibular and proprioceptive pathways that feed into the cerebellum and brainstem, supporting broader autonomic regulation

Vagus nerve / neurological focused chiropractic care — given the anatomical relationship between the upper cervical spine, the brainstem, and the vagal pathway, assessment and care of this region may be a meaningful component of neurological support for children with ASD and ADHD

Non-invasive vagus nerve stimulation devices — including transcutaneous auricular devices, which are increasingly accessible and are the subject of growing clinical research

Gut health support — given the bidirectional relationship between gut function and vagal tone

The research is not yet at the point of prescribing specific protocols or dosages for vagal support in ASD and ADHD. But the neurological rationale is robust, the emerging clinical evidence is encouraging, and the risk profile of most vagal support approaches is extremely low.

For families navigating these conditions, this is significant. It opens a door to a neurobiologically grounded approach that sits alongside — and in many cases complements — other interventions, without the side effect profile of pharmacological options.