Trauma and the Brain: Understanding Tonic Immobility

Aug 22nd, 1970

By Beth Wynkoop, SAFE/SART Policy Advocate   

When a person encounters a threat, their body responds quickly and automatically to protect them from danger. While many people have been repeatedly taught that the body always responds with “fight” or “flight” when it detects danger, this is misleading. In reality, when a person encounters a threat, they will first freeze, even if only for a split second, to rapidly assess the situation. Then, while we might expect them to go into either a fight or flight response, this is often not the case. Many sexual violence victims will instead enter a state called “tonic immobility.”

”Tonic immobility” is a rigid, unmoving state in response to intense fear. Scientists theorize that the body enters tonic immobility when the body assesses that running or resistance would increase the risk of pain or suffering.[1] This is a subconscious response that has long been studied in the animal kingdom: think of a possum going limp and “playing dead” to protect itself from threats.

Tonic immobility in humans is a newer field of study, but it is becoming clear that this response is extremely common in sexual assault victims.  When someone is assaulted, they may feel themselves becoming stiff, rigid, and unable to move, either for a portion of an assault or throughout the full traumatic event.  If you have ever heard a survivor describe that they just “froze up,” during an assault, it is likely they are describing tonic immobility.

In a recent study of sexual assault survivors, a full 70% reported that they experienced tonic immobility for at least a portion of their assault.[2] While tonic immobility is a completely normal, natural response, this does have a number of repercussions for service providers to consider. First, previous studies have found that survivors who experienced tonic immobility often feel more shame and self-blame after an assault[3]--a consequence of cultural belief in the myth that survivors should always run or fight back. In the newer study, researchers also found that survivors who experienced tonic immobility were more likely to experience depression and Post-Traumatic Stress Disorder after an assault. [4]

As Dr. Jim Hopper states in a Washington Post op-ed, “None of these responses – in women or men – entails consent or cowardice. None is evidence of resistance too insufficient to warrant our respect and compassion. They are responses we should expect from brains dominated by the circuitry of fear.”[5]

It is critical for service providers to understand normal, protective responses to sexual violence such as tonic immobility. Survivors who experience tonic immobility are at greater risk for multiple negative mental health outcomes, and any bias or blame survivors perceive from service providers may be a major barrier these survivors receiving much-needed services.

To request more information or training on the brain’s responses to trauma, contact MCASA at [email protected] or 301-728-7023.


[1] Volchan, et al. (2011). Is there tonic immobility in humans? Biological evidence from victims of traumatic stress. Biological Psychology, 88(1), 13-19.

[2] Möller, A., Söndergaard, H. P., & Helström, L. (2017). Tonic immobility during sexual assault–a common reaction predicting posttraumatic stress disorder and severe depression. Acta obstetricia et gynecologica Scandinavica.

[3] Marx BP, Forsyth JP, Gallup GG, Fusé T, Lexington JM. Tonic immobility as an evolved predator defense: Implications for sexual assault survivors. Clinical Psychology: Science and Practice. 2008;15:74–90.

[4] Möller, A., Söndergaard, H. P., & Helström, L. (2017).

[5] Hopper, J. W., PhD. (2015, June 23). Why many rape victims don’t fight or yell. Washington Post.   

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