A friend sent me a screenshot. That's how this started.
She'd been doing her own research into her child's challenges and stumbled across something called the Fear Paralysis Reflex — a primitive reflex that, if it doesn't integrate properly before birth, can leave a child's nervous system stuck in a permanent state of freeze under stress. The symptom list she sent stopped me cold. It included selective mutism. It included extreme shyness. It included the exact pattern I'd been watching in Phoebe for years.
So, there I went down a 2 week internet rabbit hole, looking for all the research, as well as scouring forums and calling up professional clinics to get more information. I learned that this is an emerging area. The research is early and a bit patchy really. I don't have clinical authority here, and I'm not going to pretend otherwise. What I have is a mother's eye, two children with different but overlapping neurodevelopmental profiles, and a growing conviction that this is worth knowing about even if the full picture isn't yet clear. So I offer up this article as a synthesis of several weeks of obsessive research!
What is the Fear Paralysis Reflex?
Primitive reflexes are the automatic movements that develop in the womb and in early infancy to support survival and neurological development. Most of them are designed to integrate — to be absorbed into the higher brain as the child grows, leaving no trace except the developmental foundation they've built.
The Fear Paralysis Reflex (FPR) is one of the earliest. It emerges at around five to seven weeks in utero, peaks at around nine weeks, and should integrate before birth — merging with the Moro reflex (the startle response) and becoming part of the brain's more sophisticated stress management system.
When it integrates properly, it leaves a child able to respond to threat with flexibility — fight, flight, or appropriate caution — and then return to calm.
When it doesn't integrate properly, the nervous system can remain prone to a very specific response: freeze. Not fight. Not flight. Just — stop. Shut down. Go still.
That response, in the context of speaking under social pressure, looks a lot like selective mutism.
The symptom overlap is hard to ignore
The characteristics associated with a retained FPR include:
- Selective mutism or inability to produce sound in certain situations
- Extreme shyness or fear in groups
- Excessive fear of embarrassment
- Withdrawal from social situations
- Difficulty making eye contact
- Clinging to familiar people; fear of separation
- Underlying anxiety or constant sense of overwhelm
- Perfectionism and fear of failure
- Hypersensitivity to touch, sound, or sensory input
- Physical freezing — the "deer in the headlights" response
I read that list and thought: this is Phoebe. Not all of it, but enough of it to then spend all those hours down my internet hole.
I also noticed something that hadn't had a name before. At home, in completely relaxed settings, there are moments where Phoebe's freeze response kicks in unexpectedly — she might say something funny and we laugh, but she will suddenly feel exposed and then freeze and cry, like something misfires. She goes still and falls apart even though she's safe, even though she's at home. That's not anxiety about school. That's something in the nervous system responding to a sudden change in stimulus. The FPR research gave me a framework for understanding it.
Why this might connect to selective mutism
Researchers have begun characterising selective mutism as a stress reaction in which the nervous system freezes, making speech physically impossible in certain situations — even when the child desperately wants to speak. One 2021 study described it as the child being "betrayed by the nervous system."
The FPR hypothesis suggests that for some children, this freeze response may have a neurological root — a primitive reflex that was never properly integrated, leaving the nervous system hyperreactive to evaluative pressure, social exposure, or sudden changes in environment. The reflex, in other words, may be firing when it shouldn't.
This doesn't mean FPR causes selective mutism. And I'm glad of that, because like a typical mother, I did spend a night crying into my pillow that it was all my fault for taking HG medication in pregnancy (at the time those reflexes were meant to be integrating, I had my head down the toilet and could barely eat anything). The research is nowhere near that conclusion. What it suggests is that for some children, an unintegrated FPR might be part of the picture — one piece of a complex presentation, not the whole answer.
What integration looks like
Reflex integration isn't a quick fix or a therapy in the conventional sense. For retained primitive reflexes generally, the approach is typically a programme of specific movements and exercises, done consistently at home over a period of months, designed to help the nervous system complete the developmental work it didn't finish in infancy or early childhood. It seems to be led by a specialist breed of magical Occupational Therapists specialising in something called Sensory Integration Therapy, and the more I learn about it, the more impressed I am.
You can search YouTube for "retained reflex testing" or "fear paralysis reflex exercises" to get a sense of what this looks like in practice — there are practitioners who have made their assessment tools publicly available. It's worth seeing for yourself.
For children who are already anxious and sensitive, the method of introduction matters enormously. Reflex integration should ideally be guided by an occupational therapist or specialist trained in primitive reflex work — someone who can assess which reflexes are retained, design a programme specific to your child, and monitor progress. It is not a process to rush.
My honest position on this
My eldest daughter — who has autism and significant sensory integration challenges — is about to start sensory integration therapy. Because in researching it for Phoebe, I realised she needed it more.
With Phoebe, I am watching and waiting. I can see the freeze response. I can see the sensory sensitivity. But my instinct right now is not to add more specialists, more appointments, more interventions to her life while we're already deep in the location ladder work and the playdate strategy. There is a real risk — one I feel strongly about — of making a child feel that something is fundamentally wrong with them through the sheer volume of professional involvement in their life. That damage is harder to undo than the original difficulty. So, I will start with her sister, and report back what the experience is like, and likely explore it for Phoebe at a later stage. It's also extremely expensive and we are saying goodbye to an All Inclusive in Turkey during October Halfterm, but hey if my eldest daughter can learn to better read when she is hungry or thirsty, that's money well spent.
This is a personal call, and every family's situation is different. But I think it's a call worth making consciously, rather than defaulting to "more is more" when it comes to intervention.
Should you explore this for your child?
Maybe. Particularly if:
- The standard anxiety-based approaches to SM haven't shifted things much
- Your child has broader sensory sensitivities alongside the SM
- You notice the freeze response happening in genuinely safe, low-pressure situations at home — not just in school or social settings
- There's a wider picture of neurodevelopmental difference (autism, ADHD, sensory processing difficulties)
If you want to explore further, look for an occupational therapist with training in primitive reflex integration. Once I uncover one I can truly recommend, I will share. There are also some good practitioner-produced resources on YouTube for testing and understanding retained reflexes — search for "fear paralysis reflex" or "primitive reflex assessment" and you'll find reputable practitioners who've made their tools accessible.
I'll be writing more about retained reflexes, sensory integration, and what we're learning through my eldest daughter's therapy journey over on my adjacent site covering autism and neurodiversity. [www.neuro-proud.com]