Friday, February 10, 2023

The Polyvagal Theory and PDA

This blog article explores polyvagal theory in conjunction with PDA (pathological demand avoidance), and includes definitions for readers who aren't unfamiliar with terms used. 

It explores how polyvagal theory can explain extreme demand avoidance, but not all of PDA. Those who are familiar with PDA, may have heard mentions of polyvagal theory in relation to it, but have struggled to make sense of it. This was my starting point when I came to write this. I felt polyvagal theory was something I *should* know, but felt helplessly demand avoidant against reading up on (such is the nature of avoidance of the PDA kind).

Thankfully, my desire to understand polyvagal theory eventually out-weighed my avoidance, and I approached Libby Hill of Smalltalk Speech and Language Therapy who specialises in PDA, situational mustism and polyvagal theory. More thankfully still, she agreed to co-author this article. It's an honour to collaborate with her because it was she who first alerted me to PDA in a series called Born Naughty! that aired on UK's Channel 4 in 2015. It's thanks to Libby, and the rest of the TV show's team, that many adults had lightbulb moments that PDA might, at last, explain their lifelong, misfit quirkiness. Some of us have gone on to advocate for PDA so awareness of our little-charted, invisible differences reaches even more people. I'm one of these, as is Riko Ryuki, who's blog you can view here.


Autonomic ladder (polyvagal theory): a spectrum of nervous system states (with feeling safe and good at the top). 

Dorsal vagal (polyvagal theory): a large, primitive part of the vagus nerve that controls body functions like digestion. 

EDA (extreme demand avoidance): an alternative name put forward for PDA (pathological demand avoidance) in response to widespread discomfort with the term “pathological” which many consider derogatory. A champion of the term EDA was Liz O’Nions who developed a scale to measure PDA named the EDAq. EDA, however, may not fully describe PDA. 

Fight / Flight / Freeze, etc: human and animal adrenaline responses which evolved millions of years ago in the animal as defence strategies to deal with threats. 

Neuroception (polyvagal theory): our inbuilt threat detection system. 

PDA (pathological demand avoidance):
    i. a distinct neurotype (brain type) that’s present from birth and is characterised by high anxiety; high personal control need; interest in people (which may become obsessive); fondness of novelty; strong, changeable emotions; using creative and/or social strategies to avoid demands; likelihood of being drawn to fantasy and role-play. PDA can be argued to fit the diagnostic criteria of the autism spectrum because it’s a life-long neurological condition impacting social communication and flexibility of thought.

  ii. a specific form of demand avoidance that gives its name to the PDA neurotype. 

Polyvagal theory: a model, put forward by Stephen Porges in 1994, of tiered nervous system states, in which the ventral vagus system operates when all is well. Sustained trauma causes the ventral vagal to shutdown and the sympathetic nervous and dorsal vagal systems to become dominant (see below for a more detailed description). 

Sympathetic nervous system (polyvagal theory): a network of nerves that are primed for the fight / fight / freeze reaction. 

Ventral vagal (polyvagal theory): a nervous system that inhibits fight / flight / freeze via social engagement and self-soothing.

Diagram showing the different polyvagal states that are described in the text

Polyvagal theory

According to Libby, if we look at the work of Deb Dana – who works a lot with Stephen Porges (the person who developed polyvagal theory) – when we're good:

  • We're operating at the top of the autonomic ladder
  • Our ventral vagal nerve is in control
  • We're relaxed
  • Can see possibilities
  • Move about the world in ease

At the same time:

  • Our sympathetic nervous system is buzzing along regulating our blood flow and heart rate
  • Our dorsal vagal system is keeping our body digesting, resting and restoring.

This is how it's supposed to work.

Depiction of things being good when ventral vagal nerve is control, and bad when it isn't

But, if our neuroception detects threat:

  • The ventral vagal shuts down.
  • Our sympathetic nervous system takes over.

Instead of the good things listed above, we:

  • Feel unease
  • Lose cognitive abilities
  • Disconnect socially
  • Mobilise for fight, flight or freeze

And our dorsal vagal system:

  • Causes digestion imbalance

If both the ventral vagal and sympathetic nervous system shutdown, the dorsal vagal takes over completely and digestive/system responses dominate:

If the dorsal vagal remains dominant, long-term issues may develop as the result of the body being in crisis for far too long (in a nervous system state it shouldn't be in). Possible health impacts are:

How polyvagal theory connects to PDA

PDA people have an essential need for personal control.

Libby explains that, according to polyvagal theory

“Tolerance and control decrease as demands and anxiety increase. This can happen for anyone, but PDA people seem to be naturally primed for it.”

Avoidance of the PDA kind is traditionally described as anxiety led need for control. This equation has, however, been brought into question by PDA people, such as myself and fellow blogger, Riko Ryuki, who say that, whilst anxiety is certainly a key trait of the PDA neurotype, our avoidance can trigger when we’re not anxious. One thing that everyone seems to agree with is that much, much more research is needed before PDA can be understood

Regardless of how anxiety and avoidance truly interact, whenever a PDA person perceives something as a demand, their inherent avoidance drive gets triggered. In polyvagal terms, the perceived demand shuts down their ventral vagus and activates their sympathetic nervous system, causing a feeling of intense ill-ease and mobilising us for fight / flight / freeze, etc adrenaline responses. As ever, more research is needed, but there’s a growing body of PDA community members who believe additional “F” responses may trigger in place of fight / flight / freeze. There’s more detail in this blogpost but, in brief, these are thought to include fawn (people pleasing), funster (playing the clown), fib (telling lies to escape being caught out) and flop (fainting or otherwise collapsing).

PDA people’s proneness to adrenaline responses can, therefore, be explained via the polyvagal theory as demands causing our sympathetic nervous system to take over.

Autism and demand avoidance

Libby says:

“All autistic people can avoid demands if their neuroception detects stressors so their sympathetic nervous system takes over. This leads to avoidant reactions like  withdrawal, shutdown and escape.”

Whilst all people could respond similarly to situations they find stressful or difficult, autistic – and other neurodivergent people – are likely to be impacted by a greater number of things, and/or be more sensitive to common stressors. E.g.:

  • Situations which trigger anxiety
  • Sensory overload
  • Disrupted routine
  • Transition difficulties
  • Things of no personal interest

Libby’s view is that when a person, autistic or not, is more avoidant than the social norm, this is EDA (extreme demand avoidance). This may seem nonsensical because the term EDA was put forward as an alternative to PDA. However, there seems to be a crucial difference, and EDA and PDA appear not to be the same thing (!) In Libby’s view, the EDAq that Liz O'nions developed – which is the only scale so far available to measure PDA – doesn't measure PDA at all; only measures demand avoidance.

EDA versus PDA

PDA people can, and do, avoid things for the reasons listed above (sensory overload, etc), but we have specific PDA-type avoidance too. Libby thinks it’s extremely difficult for people who aren’t PDA to grasp what PDA-type avoidance is. After all, it’s invisible. Libby says that a description I once gave of my PDA avoidance being like breathing strongly resonated with her and has remained in her mind.

Libby draws attention to Dr Judy Eaton's work of 2021, which suggests that specific PDA-type avoidance is rooted in avoiding one's own demands. 

This means that people can work as much as they can to reduce demands around us, but we PDA people will still be demand avoidant. Everyday demands might be avoided just because they're demands, but it's the expectation that something *should* be done that results in the inability to do it.

To put it another way, PDA-type avoidance is triggered by one's own expectations, or other people's expectations, which might not even be explicit; it could have just been implied.

So, for people with extreme demand avoidance, if you meet their needs, their demand avoidance goes away. But, with PDA, it keeps on going, unstoppably.

Whilst extreme demand avoidance is logical, as we’ve seen, PDA-type avoidance is very hard for someone without PDA to understand.

It should also be borne in mind that PDA, as a neurotype, entails a cluster of additional traits, such as social focus and propensity for fantasy & role-play. This will be the subject of a follow up blog article.
Libby believes that autism plus demand avoidance is actually very common, but PDA is, relatively, really rare.

Internalised PDA and my own thoughts on the EDAq

It’s maybe worth mentioning that a growing number of adult PDAers, such as me, have been coming forward to say that we match all the traits associated with the PDA neurotype, but internalise our stress, meltdowns and avoidance strategies, etc so that the existence of our PDA is effectively hidden (you can read more in a blogpost I wrote on the subject). I was concerned that the EDAq might not pick up internalised PDA, because it includes things like telling classmates what to do and social interaction having to be on “their own terms”. Whilst we internalisers might be happy if these things happened for us, we’ll be very unlikely to externalise our feelings, and be more likely to feel depressed and alienated because we don’t comfortably fit in socially.

I contacted Liz O’nions in 2018 to ask if her EDAq scores internalised presentations of PDA, and she confirmed that it doesn’t. 

Another issue I have with the EDAq is that much of its wording is riddled with observer assumptions which make it a minefield for actually PDA people to answer honestly and still score enough to be, in the scale’s words, “identified [as] those at high risk of showing features of Extreme Demand Avoidance”.  

Examples are: 

  • “shows little shame or embarrassment (e.g. might throw a tantrum in public and not be embarrassed)” 
  • “likes to be told s/he has done a good job”, the latter giving a negative score for answering yes. 
This is problematic because the reality of PDA is that, whilst we tend to find general praise squirmy, we often crave specific praise for things we’ve done.

As for Libby’s assertion that it doesn’t score PDA at all, my internal jury is out. Its criteria list does contain things that apply to the broader PDA neurotype, such as “invents fantasy worlds or games and acts them out” and “uses outrageous or shocking behaviour to get out of doing something”, which aren’t traits associated with autism in general. However, I agree that the EDAq fails to encapsulate what PDA actually is. It touches on it, but misses much. 

Could a non-PDA person score highly enough in the EDAq to be “identified [as] those at high risk of showing features of Extreme Demand Avoidance”? Possibly, but I can’t say for sure. As ever, more research is needed. What I can confidently say is that the wording of the EDAq will miss a lot of actual PDA.

Depiction of the polyvagal system describing extreme demand avoidance, but not PDA

Why polyvagal theory accounts for EDA but not all of PDA

We’ve seen that, according to polyvagal theory, perceived demands trigger PDA people’s neuroception so our ventral vagal shuts down, and our sympathetic nervous system & dorsal vagal take over, leading us to be fight / flight / freeze primed and prone to developing chronic health issues, like irritable bowel syndrome.

We’ve also seen that EDA and PDA are different entities. EDA, aka extreme demand avoidance, can be experienced by anyone and is alleviated if needs are met so – in polyvagal terms – the ventral vagal nerve takes over running things.

However, what polyvagal theory doesn’t explain is the cause of PDA-type avoidance. Its neurological origins and mechanics remain a mystery: why are we specifically triggered by things that we perceive as a demand?

Neither does polyvagal theory explain why removing the feeling of “demand” from something reduces our avoidance. 

If PDA brains simply detect more threats than non-PDA brains, why does it matter if things do, or don’t, feel like demands? Surely, we’d feel just as threatened by the idea of going somewhere if we didn’t feel we had to? If the presence of demand makes no difference, then this is surely extreme demand avoidance, not PDA?

I think this is a crucial distinction. Unless the specific, irrational nature of PDA-type avoidance is understood, people won’t credit PDA’s existence, and we sorely need our existence credited.

Need for differential diagnosis

Libby is very concerned that, if diagnoses don't distinguish between EDA and PDA, we risk making the issue worse. 

For example, if we were to use typical autism strategies for a PDA child, that would be dreadful. On the other hand, for children with extreme demand avoidance who are autistic, using PDA strategies could make things worse, because we wouldn't be giving them the structure or routine that they need to make them feel safer.

Correct diagnosis clarifies which approaches to use and should, in the ideal world, allow access to services. The key thing though is highlighting the radically different management strategies for school, and also home. PDA, after all, throws most parenting on its head. People need to grasp that, with PDA, it's "can't not won't".

This high need for differential diagnosis has led Libby and nine other professionals involved with PDA – including Phil Christie, Judy Eaton and Gloria Dura-Vila – to collaborate to put together a formulation to present to the diagnostic manuals. However, after two years, they've realised they're still far from achieving this goal. 

The more they've looked at tightening the definition of PDA and making it more specific, the more they've realised it's not straightforward. 

The presence of PDA is something they can feel, but this isn't tangible enough to put down on paper; it's not scientific; you can't put it in a manual.

For robust diagnosis – speaking of children – they need to be seen by more than one professional and in more than one situation. It's about listening and observing and taking everything in; not just what's said and done, but looking behind that. ADOS and DISCO (more info) rely on parental reports, which is insufficient to distinguish between EDA and PDA. The Coventry grid is a good tool, especially the version of it Judy Eaton amended to look at PDA. 

Another issue is that clinicians' knowledge varies (wildly). Many, for example, have no idea that there's a difference between EDA and PDA – and this is for ones who accept that PDA exists at all.

It's really early days and we've got to build on what we know.

Sometimes, if we say they need a bespoke package, this takes away the need to work out if it's EDA or PDA.

The team will be coming back to their collaborative mission to pin PDA down into a definition diagnostic manuals can accept.



  1. Hello, I may have misunderstood/ misread, but I think there may be a slight inaccuracy in your writing on Polyvagal Theory. You haven't made a distinction between the sympathetic nervous system that is responsible for fight or flight and the parasympathetic nervous system that is responsible for freeze (but also 'rest and digest').

  2. Hello, I've run this past libby, the co-author and she's clarified that sympathetic nervous system reactions account for shutdown, which is different from freeze