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The Biological Basis For Defense Mode (Understanding The Vagus Nerve)

Danny Raede


Do you feel that? Right there in your chest. . . Listen. . .

That’s your heart. That’s what’s keeping you alive right now.

If you’re like most people, your heart will have beat roughly 4,800 times in the last hour (80 times per minute). However, what you may not realize is that not all of those beats were exactly the same. Most people’s heartbeat tends to be pretty steady but not perfectly so. Some beats happen a little faster and therefore closer together. Others are just a little slower and farther apart. That variation between your heartbeats has a special (though not very original) term: Heart Rate Variability.

A little ways behind your heart is your spine, which supports your neck and head and runs down to your tailbone. Do you feel it there? Strong and steady, it’s got your back (pun intended). Running along and through your spine are a lot of different nerves, all of them important. However, for today, we’re going to focus on just one them: the vagus nerve (pronounced like Las Vegas, but spelled differently). It plays a role in a lot of critical functions, a couple of which are controlling your heart rate and the regulation of the stress response (fight, flight, or freeze). Basically, the vagus nerve’s job is to keep your heart rate steady, calm you down, and then keep you calm.


The Vagus Nerve

Because of the vagus nerve’s direct connection to the heartbeat, there’s this handy method of measuring how well it’s doing its job: measuring your heart rate variability (HRV) (see graph below). If your HRV is crazy and all over the place (high variability), then your vagus nerve is currently struggling. You have what’s called Low vagal tone, and chances are excellent that you get stressed out more easily. You probably tend to feel more anxiety, and in general, it’s just harder for you to regulate and deal with negative emotions. Low vagal tone is often seen in individuals with PTSD (Post Traumatic Stress Disorder).


On the flipside, we have those with high vagal tone. Here you have an HRV that almost runs like clockwork. Of course, there’s still some variation. We live in reality after all, and reality means stress is inevitable. However, individuals with high vagal tone are less reactive to that stress. It is easier for them to deal with difficult situations and negative emotions as they arise. They’re cool as a cucumber. They’re able to take things as they come, and let it roll off them, like water off a duck’s back.

So who cares? Why I am I boring you with all this science stuff? Good question.

Here’s the bottom line: low vagal tone = Defense Mode. They go hand-in-hand. Defense Mode is a state in which someone with Asperger’s is scared, frustrated, or angry, as well as shut down and withdrawn. On the behavioral level, Defense Mode typically manifests as some variation of fight, flight, or freeze.

Low vagal tone is a state in which someone is naturally more susceptible to stress and negative emotion, and therefore more likely to react with fear and anger. They’re more likely to lash out, run, or shut down. Fight, flight or freeze.

This matters because I want you to understand that that there is a real, biological basis for why your Asperger’s child is in Defense Mode and has fewer spoons than you. You can literally measure it with an ECG (electrocardiogram).

When your child is in Defense Mode, they will naturally have fewer spoons because they’ll lose them more quickly. A stressor that feels imperceptibly minor to you might feel enormous to them. Even positive emotions, like excitement, can feel overwhelming to your child and can be draining in their own way. Your child’s vagus nerve is not functioning at full capacity, and therefore they are not physically capable of regulating their emotions and stress response the same way you do. They are often a lot closer to their breaking point and can become overwhelmed more quickly.

Please recognize that this not some sort of moral failing on their part. We don’t yet fully understand why trauma (like being in a warzone), or the innate neurological differences of Autism (such as sensory issues) cause damage and inflammation to one’s vagus nerve, but we know it happens. More importantly, we know that there is a real, biological basis for Defense Mode, overwhelm & shutdown, and that science can now prove that people on the spectrum aren't just being "lazy".

Note: This is an excerpt from our book "7 Easy Ways To Motivate Someone With Asperger's". Get the whole book here.

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Hi Danny...

I’m looking for help with a 40young woman, my daughter. She was dxd at 14 and is now having problems with meds. Can you point us in the right direction.

Thannk you


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Please share the exercices or process we can use to stimulate or relax this vagus nerve. A treatment exists to stimulate the vagus nerve for epilepsy patients by sending an electric current through the ear, doctors have also used this to help long COVID patients recently. Is this something that might help with Aspergers ?

Catherine Drouet

Brussels, Belgium

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