When a person or animal experiences a dangerous situation, each will typically react with an inborn fear/defense mechanism, such as the well-known "fight or flight."

In a new article, published in the Harvard Review of Psychiatry, researchers offer a detailed framework of the "defense cascade," a five-step series showing different types of fear/defense responses.

Although both humans and animals react to fear in similar ways, animals are able to return to their normal mode of functioning once the danger has passed.

However, "Humans often are not, and they may find themselves locked into the same, recurring pattern of response tied in with the original danger or trauma," said researcher Dr. Kasia Kozlowska, a child and adolescent psychiatrist from the Children's Hospital at Westmead, Australia.

Understanding the steps of the defense cascade may lead to better treatments for patients dealing with these persistent aftereffects of trauma.

In the study, the researchers review the characteristics and neurobehavioral basis of the defense cascade, "a continuum of innate, hard-wired, automatically activated defensive behaviors" in response to threats. In humans as in animals, the cascade occurs in a series of the following five steps:
  • arousal: muscles tense, breathing, and heart rate increase as the body prepares for action;
  • fight or flight: active defense response for dealing with threat;
  • freezing: a fight-or-flight response put on hold;
  • tonic immobility: inability to move or call out; shut down in the face of fear. A variation is collapsed immobility, with loss of muscle tone and changes in consciousness. Tonic and collapsed immobility are "responses to inescapable threat or strategies of last resort;"
  • quiescent immobility: after the threat or danger has passed, a state of quiescence that promotes rest and healing.
The article presents clinical accounts of traumatized patients with reactions corresponding to each step of the defense cascade. For example, a combat veteran may react with suspicion and rage (fight or flight) to perceived threats; traumatized children may experience episodes of withdrawal or fainting (tonic or collapsed immobility) when reminded of their experiences.

Recognizing and understanding these reactions enables clinicians to develop treatments "to manage the mind-body states that are the human expression of the defense cascade."

Clinicians can offer the patient targeted interventions designed to decrease arousal, target processing of traumatic memories, and manage mind-body states reflecting each step of the cascade.

Also, simply understanding the biological basis of the defense responses can help alleviate guilt or other negative emotional reactions experienced by some trauma victims.

The researchers believe that their framework can help mental health professionals, including those working with clients in the military or law enforcement or assisting victims of sexual abuse, to understand the responses that make up the defense cascade.