Trauma and PTSD

The Neurobiology of Traumatic Fight/Flight/Freeze

The neurobiology of trauma and the fight/flight/freeze response

A couple of years ago I was thinking about applying for a nursing job with a sexual assault support team, so I decided to learn more about the body’s fight/flight/freeze response to trauma.  What I found out was really interesting, so I thought I’d share.

The amygdala’s response

The amygdala is a primitive part of the brain that processes emotional reactions and memories related to threats.  The amygdala automatically reacts to rape as a potentially life-threatening event, regardless of whether the victim knows the perpetrator or not.  It triggers the activation of the fight/flight/freeze response, stimulating what’s known as the hypothalamic-pituitary-adrenal (HPA) axis to release a rush of hormones, including cortisol, norepinephrine, endogenous opioids, and oxytocin.

The traumatic hormone soup

The prefrontal cortex, the most evolutionarily advanced part of the brain, takes a backseat when the amygdala starts going full-throttle.  Norepinephrine starts flooding the prefrontal cortex, and logical reasoning, rational decision-making, and higher-level regulation of thoughts and emotions all go right out the window.

The body naturally makes its own opioids, including endorphins, which it releases in threatening situations. It makes sense if you’re a caveman running from a tiger and the amygdala doesn’t want pain slowing you down.  This also tends to flatten people’s affect (facial expression of emotions) for several day. This may appear strange for people who think that a victim “should” have a visible emotional reaction if they were traumatized.

Oxytocin tends to be known for its role in pregnancy and mother-infant bonding, but it also counteracts pain.  It’s released as part of the hormone soup of trauma, and one of the odd effects is that it can cause victims to laugh while recounting the traumatic events.

Tonic immobility

The freeze part of the fight/flight/freeze response is impacted by cortisol and the simultaneous activation of both the sympathetic and parasympathetic nervous system.  One source I looked at said up to 50% of rape victims experience “tonic immobility”, which involves muscle paralysis while still maintaining awareness.  Another source said that this happens in up to 85% of victims. This response tends to be more likely in people who’ve previously been assaulted.

Critical incident amnesia

There is also an effect called “critical incident amnesia”  Recall begins to improve after the first night of sleep post-incident, but it’s only after the second night of sleep that the memories become fully accessible.  Alcohol can impair the encoding of contextual details of memory, but sensory information still gets encoded (particularly smell, due to the location of the olfactory bulb in the brain).  Those sensory details can serve as a gateway to access memories of the event.

There’s no “right” way to react

Society has so many expectations of how people “should” look/feel/act.  People think that they can predict how someone “should” “rationally” react to trauma.  But that caveman amygdala has been around a heck of a lot longer than all these “shoulds” and rationality. When it’s in the driver’s seat slamming on the gas of the fight/flight/freeze response, it’s doing its own thing.  What people “should” do, including police and judges, is drop the victim blaming and educate themselves.

There’s a list of more posts on trauma in the Blog Index.


cover of PTSD Treatment Options: An Overview from Mental Health @ Home

The MH@H Store has a mini e-book on PTSD Treatment Options: An Overview that covers a number of evidence-based therapies for PTSD.  It’s also available as part of the Therapy Mini-Ebook Collection.

The blog index includes s list of posts related to trauma.

16 thoughts on “The Neurobiology of Traumatic Fight/Flight/Freeze”

  1. You never know how your are going to react until it happens. My reaction both during and after was completely different than what I would of thought it would of been. The rape crisis center was especially helpful in helping me understand my reactions weren’t as puzzling as they felt.

  2. Very informative! I totally agree with the concept that there’s no “right” way to react to any form of trauma. Whenever I watch those murder mystery shows like 48 Hours Mystery, and the police say, “Her reaction to her husband’s murder was very suspicous,” I’m sitting there thinking, “Um, maybe she was in shock?” You just can’t put a “normal” response on anything horrific. So I’m all like, “Show me some evidence that she’s the killer, because the way she reacted to his death tells me nothing.”

    I hope police know that fact you mentioned about rape victims’ memories not being fully returned for a day or so. I can’t imagine how frustrating it would be to not be fully heard because you didn’t know.

    Regarding rape, a really good, must-read document is the victim’s statement in the Brock Turner case. https://www.documentcloud.org/documents/2852615-Stanford-Victim-Letter-Impact-Statement-From.html

    Great post!!

      1. It sure is! Sorry… I hope I didn’t bring you down with it! 😮 I cried when I first read it! I really admire her attitude and her fortitude. She’s such a great role model, and I’d love for her story to be required reading for middle school students!

  3. After reading your post and learning so much your statement “What people “should” do, including police and judges, is educate themselves” was a fantastic way to end it as its horrible to assume that everyone should respond the same way to trauma. Thanks for sharing as I learnt a lot 🙂

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