What Happens To the Brain During Sexual Assault?

Exploring the science behind the state of "Tonic Immobility," that occurs during sexual assaults

Theme: Health Issues and Disease, Ethics and Controversy

Zuairia Shahrin

“If I were her, I’d fight with all the power I have inside of me.” 

“If I were him, I wouldn’t have gone there in the first place.”  

Many victims regretfully say that they “froze” during the sexual assault. And it’s easy for society to expect victims to retaliate when an assault occurs. But it’s not so simple. The brain can react in various ways depending on the situation. Sometimes, it supports us. Often, it doesn’t. Today, this article aims to highlight how the brain processes a sexual assault, and why it might not be helpful during an assault. 

Memory processing is divided into 3 stages: encoding, storage, and retrieval.[1] For any event we experience, we don’t take in all the details. What our brain encodes depends on what we are highly attentive to, and what has emotional significance to us. These are known as the central details. The details we aren’t paying attention to don’t get coded very well, hence are known as peripheral details. During storage, the encoded information is retained in the brain. What our brain perceives as central detail is retained, and peripheral details quickly fade unless remembered and re-encoded. As we sleep, our brains are filtering and prioritising mainly the central details. Due to the “negativity bias,” we tend to remember central details of negative experiences more clearly because the brain encodes those memories strongly, to enable survival in a world full of danger. In the last stage of retrieval, memories generally fade because they become abstract scenarios over time. We only remember a couple of central details and a general gist of the incident.[1][2]

The information that the brain receives during an assault is heavily variant. Some specific parts of our brain make up the “defence circuitry” that is responsible for detecting threats.[4][7] When the defence circuitry receives sensory information that may indicate danger, it starts to dominate the functions of the brain. The amygdala, which feels fear, recognizes an assault as a threat and sends signals to the hypothalamus, which then signals the pituitary gland, resulting in the secretion of many hormones from the hypothalamic-pituitary-adrenal axis.[3] During the assault, a hormone called catecholamine is secreted from the adrenal gland. Although it stimulates the “fight or flight response,” this hormone also impairs the prefrontal cortex, which is the centre of rational thoughts. Blocking physical and emotional pain during the assault, a morphine-like hormone called opiate reduces the scope of communication. The victim’s voice becomes monotone as the opiate does not allow emotions to be expressed.[3]

The victim could think that they’re screaming, but it becomes a whisper in reality. 

Reducing the energy level in the body, a group of steroid hormones called corticosteroids freeze the body into a state of the shutdown called tonic immobility. As the “fight or flight” response fails, breathing becomes heavier and eyes close. Muscles sink into paralysis because of the incredible state of fear. Despite trying their best to do so, a victim cannot move or speak in this state.[3] It is almost impossible to have rational thoughts at this point. The brain is unable to plan or weigh options that make informed decisions. With the absence of any thought or behaviour, the defence security unleashes a surge of stress chemicals that rapidly impair the prefrontal cortex. When this happens, all we are left with are past habits and reflexes. Unfortunately, these may not be enough to retaliate. When thoughts do rise again, the prefrontal cortex remains incapable of complex rational thinking.[4]

Once he/she manages to emerge from the shock, the victim’s thinking is severely minimized. Whilst some are fixated on single thoughts such as, “This can’t be happening” or “God please help me,” others find themselves confused between two extremities of choices, like: Scream and let people see me in an objectionable position vs. lie still and quiet. Run naked out the door vs. wait for it to end. Fight back and risk even worse violence vs. offer no resistance at all. With the impaired prefrontal cortex making them think that these are all lose-lose options, most victims tend to choose option 2.[4]

Every incident of sexual assault or extreme sexual harassment is unique. In some brains, all movement and thinking come to a sudden stop. Some people might have a blank mind and no behaviours to choose from, while others feel that the brain has cued up only extreme behaviour options, with the prefrontal cortex having little to no capacity for rational thinking. In all of these cases, the brain is helpless, failing to choose one option, let alone come up with something potentially more effective.[6]

So what’s the solution?

Think of militants who train every single day to protect themselves and others around them. Reducing instances where the victim experiences a “freeze” through self-defence training can sharpen reflexes and improve habits.[5] In doing so, a victim could be better able to handle the situation of assault. Whilst we can’t assume that self-defence training will be the permanent solution to such horrific happenings, we should also understand that holding the victim responsible for not retaliating is victim-blaming and it will only lead to more psychological and emotional trauma for the victim. By educating ourselves and others about how the brain responds during an assault, we can adapt our approaches to dealing with victims, helping them cope with the impacts of this horrific experience.


  1. Negativity bias: The notion that even when of equal intensity, things of a more negative nature have a greater effect on one’s psychological state

  2. Defence circuitry: A defense system made to protect us from all manner of attacks and high-stress situations

  3. Amygdala: Part of the brain responsible for experiencing emotions 

  4. Hypothalamus: A small region of the brain that releases hormones and regulates body temperature

  5. Pituitary gland: A gland that plays a major role in regulating vital body functions and general wellbeing

  6. Hypothalamic-pituitary-adrenal axis: Consists of the hypothalamus, pituitary gland and adrenal gland receiving messages from one another

  7. Catecholamine: Hormones made by the adrenal gland that regulate heart rate when a person is stressed

  8. Adrenal gland: Located on top of both kidneys, producing a range of hormones that regulate metabolism, immune system, blood pressure and other essential functions

  9. Prefrontal cortex: Part of the brain responsible for complex cognitive behaviour, personality expression, decision-making and social behaviour

  10. Morphine: Medication that decreases the feeling of pain

  11. Corticosteroids: Drugs that lower inflammation in the body

  12. Tonic immobility: Temporary state where motor functions are inhibited, in response to situations involving extreme fear


  1. Hopper, J. (27 September 2018). How Reliable Are the Memories of Sexual Assault Victims? Scientific American Blog Network. Retrieved 10 May 2020. [Online] Available from: <https://blogs.scientificamerican.com/observations/how-reliable-are-the-memories-of-sexual-assault-victims/>

  2. Martin, R. (28 September 2018). The Effects Of Sexual Assault On The Brain. NPR. Retrieved 10 May 2020. [Online] Available from: <https://www.npr.org/2018/09/28/652499078/the-effects-of-sexual-assault-on-the-brain

  3. Arkansas Coalition Against Sexual Assault. (2019). What Happens to the Brain During a Sexual Assault? ACASA United States. Retrieved 10 May 2020. [Online] Available from: <https://acasa.us/what-happens-to-the-brain-during-a-sexual-assault/>

  4. Hopper, J. (3 April 2018). Freezing During Sexual Assault and Harassment. Psychology Today. Retrieved 10 May 2020. [Online] Available from: <https://www.psychologytoday.com/intl/blog/sexual-assault-and-the-brain/201804/freezing-during-sexual-assault-and-harassment>

  5. Hopper, J. (5 September 2018). Why It’s Time for Sexual Assault Self-Defense Training. Psychology Today. Retrieved 10 May 2020. [Online] Available from: <https://www.psychologytoday.com/intl/blog/sexual-assault-and-the-brain/201809/why-its-time-sexual-assault-self-defense-training>

  6. Hopper, J. (22 January 2018). Sexual Assault and Neuroscience: Alarmist Claims vs. Facts. Psychology Today. Retrieved 10 May 2020. [Online] Available from: <https://www.psychologytoday.com/intl/blog/sexual-assault-and-the-brain/201801/sexual-assault-and-neuroscience-alarmist-claims-vs-facts>

  7. Hopper, J. (19 December 2017). In Most Sexual Assaults, “Defense Circuitry” Runs the Show. Psychology Today. Retrieved 10 May 2020. [Online] Available from: <https://www.psychologytoday.com/intl/blog/sexual-assault-and-the-brain/201712/in-most-sexual-assaults-defense-circuitry-runs-the-show>


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