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Fight, Flight, or Freeze: Threat Responses Explained

Many have heard of the “fight-or-flight” reaction to fear and then the “freeze” that often follows. Fight, flight, or freeze are natural bodily reactions that have adapted over time for our survival. But it turns out that there’s more to “fight, flight, freeze” than we initially thought, starting with the defense cascade.


The Defense Cascade 

As described in the Harvard Review of Psychiatry, our threat responses actually go through a system called the “defense cascade.” The defense cascade includes fear as a stimulating threat, followed by fight, flight, freeze, tonic immobility, collapsed immobility, and quiescent immobility. Threat responses have evolved similarly and are most often studied in animals. In this study, the defense cascade response was compared in both humans and animals. In humans, researchers found that the defense cascade travels through the brain and body to stimulate the reaction. This chart illustrates the various responses, which are described in detail below.



Arousal is the first step of the defense cascade. When arousal occurs, the heart pumps faster, and muscles may tighten to prepare for one of the next steps. Sometimes arousal will immediately stimulate the fight-or-flight response, but most of the time, it leads to the freeze response. When a threat is perceived, the brain and body’s arousal response travels to stimulate the hypothalamus pathway response. First, the autonomic nervous system (voice box) is tightened, and the somatomotor system is activated (when muscles tense). Sometimes this activation will also restrict the movement of blood vessels to the salivary glands, resulting in a dry mouth and a high, squeaky voice. 



The fight-or-flight response can follow the arousal response. Fight-or-flight is characterized by the brain and body’s decision to either fight and attack the threat or flee the threat as fast as possible. For example, when faced with a spider, some people will immediately try to whack it while others will run to escape the room. A few distinct brain and body responses happen at the same time: the stimulation of the somatomotor component (muscles), visceromotor component (voice box), and the pain-modulation component (pain or perceived pain from threat). 

The fight-or-flight response is most common in children who’ve been traumatized, who tend to either run away or fly into a violent rage. Those who have post-traumatic stress disorder (PTSD) often have impaired functioning in their arousal response, making them skip immediately into fight-or-flight. 



In the case of freezing, the person perceives a threat, knows to freeze, and maintains the ability to scan their surroundings and wait for their next move. For example, when a person accidentally starts a fire, they may freeze temporarily, then “wake up” and begin to put the fire out. For this to happen, the arousal stimulates both sympathetic and parasympathetic reactions. 

The sympathetic reaction is the activation of the heart, lungs, muscles, brain, gut, and voicebox. The parasympathetic response halts and holds the sympathetic response still. The brain activates both the freeze parts and the fight parts at the same time, making them all but cancel out. Due to the fear response, the heart (though stimulated) may change rhythm, causing the muscles to freeze and the body to tensely wait. Perceived pain is temporarily stopped as well. Once the heart re-starts, so will the lungs and body.


Tonic Immobility

Tonic immobility is another form of the freeze response when the victim plays dead. This happens in many animals and humans. Historically, tonic immobility is the body’s response to when fight-or-flight has failed, and the threat has won over the victim. The body freezes, can be moved unnaturally, and may feel no pain or dull pain due to the inhibited response from the brain and body. In some cases in humans, including rape victims, the body can feel pain and still be in a state of tonic immobility. This response can also happen in war victims, those attacked by wild animals, those in car wrecks, etc. 


Collapsed Immobility

This is also known as fear-induced fainting or collapse. Collapsed immobility is the brain and body’s response to extreme fear or triggers. A common fear for humans that can trigger the collapsed immobility response is the sight of blood. The hypoxia from the brain’s stimulated fight-or-flight, which is canceled by the freeze, can create a state of hypoxia (or low blood oxygen) that causes the person to pass out.


Quiescent Immobility

Quiescent immobility is the body’s freeze response to extreme pain, which can last for days and be very traumatic. There are methods to alleviate the response for those who have prolonged or extreme reactions to the defense cascade. In most cases, help from a doctor, therapist, or mental health professional is needed. Talk to your provider for more information on how you can get help for handling overwhelming fear and improve your mental well-being. 


If you’re suffering from a constant state of fear or unsure how to alleviate your fear response, learning more about fear responses and coping strategies can help. At RECO Intensive, we understand that when the fear response (or defense cascade) is stimulated, sometimes scary and traumatic events follow. These traumatic events can leave mental scars that last a lifetime and trigger responses you don’t want to deal with. At RECO Intensive, we believe that your fear is valid, and we want to help you get through it. Our specialized staff and experienced alumni can guide you through your fears, help you conquer addiction issues, provide therapy for mental health battles, and provide a safe space for all of this to happen. RECO Intensive works with your unique needs and your schedule to help you reach your mental health goals. Call RECO Intensive today at (561) 464-6533. Let’s get back to a brighter future. 

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