How Trauma Affects the Brain


By Molly Keeton, Ph.D.

Trauma is a word that we use and hear often, but what is trauma? It is usually defined as the experiencing or witnessing of an event(s) that is threatening or dangerous and out of one’s control. Trauma usually involves a feeling of helplessness. Many people serving in the military experience trauma, as do individuals who survive a natural disaster, serious accident, or personal assault. While these are common examples of trauma, experts generally agree that what makes something traumatic to a person is determined by their response to it, rather than whether someone else considers it “traumatizing”. For example, a student who was humiliated by a parent or teacher while growing up may have experienced a trauma.

The best way to determine if an event was traumatic in your life is simply to look at the impact it has had. Do you continually think about the event, even when you do not intend to? Do you sometimes experience the feelings that you felt during the event or even feel as if you are experiencing the trauma again? Do you avoid reminders of the event by steering clear of certain places, people, or topics of conversation? Do you have nightmares related to that event? Do you find yourself on edge, expecting danger, or responding differently than others to certain events (for example, a veteran may hit the floor when they hear a car backfire, thinking that it is a gunshot. Or a woman who has survived sexual assault may be untrusting of all men)?  Are these symptoms getting in the way of your relationships, goals, sense of peace and safety, or general life satisfaction? If you answered yes to even a few of these questions, you may be dealing with Post Traumatic Stress Disorder (PTSD), an anxiety disorder that may occur after a traumatic event. While these responses are normal and expected after a trauma has been experienced, PTSD occurs when they go on for weeks, months, or even years after a trauma.

Trauma can have dramatic and long reaching effects on an individual’s life. Learning more about the neurological processes involved may provide information about why trauma impacts us the way it does, increase empathy for oneself and/or others, and promote awareness that healing can occur.

Development of the human brain

The human brain contains three distinct parts that developed in this order: the reptilian brain, the mammalian brain, and the cortex (or neo-cortex). Higher level functions, such as planning, developed later than the more primitive capacities, such as aggression.

The reptilian brain

The oldest and most primitive part of the brain. Primary task is survival. Controls breathing, balance, and temperature regulation. Acts out of instinct.

The mammalian brain

Includes the limbic system, which is the emotional center of the brain. Involved in the control and expression of emotion, the body’s response to danger, and the processing of short term memory. Primary focus is also survival.

The cortex (or neo-cortex)

The most recent area to develop within the brain. Allows for higher level thinking, analysis, logic, and intellectual pursuits. Cortex is always overridden by reptilian and mammalian brains.



Despite how humans have evolved, the primary task of the brain remains self-preservation and propagating of the species. The functions of the reptilian and mammalian brains will always override the neo-cortex, as our very survival is dependent upon this. Because threat has a far more immediate and powerful consequence than reward, the brain is overdetermined to sense and respond to danger.

The brain receives data from the outside world through the five senses. This sensory information comes in through the thalamus and is directed either towards the limbic system or the cortex. If threat is perceived, the sensory input goes first to the brainstem and midbrain (limbic system). In this case the limbic system attempts to match the data against information and patterns that have been stored from past experience. If threat is perceived or if the data matches a template for danger, the alarm response of the brain is activated. The limbic system is quite complex and contains many different structures. For our purposes, we will focus on two of these structures: the amygdala and the hippocampus.


The Amygdala

The amygdala is the part of the limbic system responsible for processing and assigning emotional value to incoming sensory information. It is a tiny, almond shaped structure at the core of the limbic system. It is over 50,000 years old and was designed to protect us from threats such as a saber-tooth tiger. The amygdala functions sort of like a pass-fail exam. When trying to decipher between something that might bring pleasure and something that might bring death, every piece of sensory data must be quickly sorted into only one of two categories – safe or unsafe.

If the amygdala perceives a threat, it immediately springs into action and does not wait around for the cortex to analyze the data and return a verdict (i.e. “that man reminds me of someone dangerous because he has a similar hairstyle, but he is very clearly not the person who hurt me in the past). Although the limbic system and cortex have many interconnecting neurological pathways, communication to the cortex may be cut off in this moment of danger. When the potential for severe injury or death is imminent, there is simply no time to stop and make logical evaluations or interpretations. Remember that this system evolved to protect us from tigers and other such predators. It would be a waste of precious time if in the midst of being charged by a tiger one stopped to compare it to other tigers in that region, estimate its size or velocity, or begin planning the best strategy for escape.

Before any conscious awareness has occurred, the amygdala activates the Autonomic Nervous System (ANS), which enlists every area of the brain and body to respond to the threat and deactivates all non-crucial bodily functions, such the digestive and immune systems. The amygdala also determines the best response to a threat, including the fight, flight, and freeze responses. If the limbic system perceives that there is enough strength to defend oneself, then fight will be chosen. If adequate time, strength, and distance to allow for escape is perceived, then flight will be chosen. In both cases it is the sympathetic branch of the ANS that responds, resulting in increased respiration, heart rate, oxygenation of the blood, and blood flow to the muscles for mobility and strength.

If time, strength, and distance are not determined to be sufficient or if death could be imminent, then the parasympathetic nervous system is activated. This branch is associated with resting and relaxation and leads to the freeze response.  This can be seen in nature when a mouse being attacked by a cat goes limp, oftentimes resulting in the cat losing interest and the mouse surviving.  As a teen I participated in a 3 week wilderness course where I was given similar advice. If I encountered a bear and was within close enough range to see it, there would be no way for me to outrun that bear. Outfighting it was obviously out of the question. My best defense would be to drop to the ground and hope that it would get bored of me before inflicting too much bodily harm.  This is VERY important information if you are a person who ever blamed yourself for how you responded to a trauma. Your reaction was not a thinking process and was not up to your conscious mind. It came from an instinctive part of your brain that is very, very old and very well programmed to protect you from any avoidable danger.

The Hippocampus

The hippocampus is a structure in the limbic system that is associated with learning and memory. The hippocampus stores memory of time, place, and space in time. It organizes memories in a chronological way. Because of the heavy activity of the Limbic and autonomic nervous systems during a traumatic event, traumatic memories are believed to get stuck in the lower and mid portions of the brain (reptilian and mammalian brains) where they cannot be accessed by the frontal lobes of the neo-cortex. While normal, non-traumatic memories get filed away in various places of the cortex, traumatic memories are not processed or integrated in the typical way.

While this may seem like a cruel joke of nature, there is a good biological reason for it. When the limbic system perceives a threat, it activates the ANS to release hormones to enhance the fight, flight or freeze response. These hormones not only activate the body to physically respond but also supercharge the memory function of the brain (it should really only take one run in with a shark for the body to imprint that this is a dangerous situation). The amygdala is basically sending a strong message that whatever just occurred needs to be remembered and remembered very well. In this state of arousal, the body continues to release hormones such as adrenaline, which, over time, can damage connections within the brain (it can also cause damage to the heart and the immune system). Research has also shown that adrenaline can ultimately shrink the hippocampus – further reducing its ability to place memories in time and space.

The brain is constantly in the process of receiving data, interpreting and analyzing it, and creating action based on that data. It has an enormous capacity to store information and use that information over time. The human brain increases its efficiency by creating internal representations of the external world, or templates. These associations generalize to future events. For example, when I see a door, my brain instantaneously recognizes this and sends a message to my muscles about how to respond. From time to time I may come upon a door that looks nothing like any door I have ever seen in the past, but still my brain can compare it against the template it holds for doors and respond appropriately. This is true of all sensory input, whether it comes in through site, sound, smell, taste, or touch. The sense of smell has been found to make particularly powerful associations in the brain. This is especially evident with Post Traumatic Stress Disorder (PTSD) – oftentimes a familiar scent can trigger the autonomic nervous system faster than anything else. (If you look at a diagram of the brain, you will notice that the olfactory bulb, which is responsible for sense of smell, is located within the limbic system).

Brain Plasticity

The brain is modified by all experiences, whether they be positive or negative. This is because it has plasticity, meaning that its architecture and pathways of communication can be modified over time. Some areas of the brain, such as the cortex, have more plasticity than others. It is relatively easy to learn the concepts being presented in this paragraph (cortex) but quite difficult to learn to ride a unicycle (reptilian brain). The brain develops and is organized in a use-dependent fashion. It is commonly accepted that “neurons that fire together, wire together”, so the more a neural system is activated and used, the more it will adapt over time. The greater the activity within a neural system, the more the system will develop capabilities related to that type of function. This is true for playing the piano, learning a second language, or responding to a threat – more “practice” means the response becomes more engrained. Once a brain area is organized, it is has less plasticity and is less receptive to incorporating new data (again, it is harder to learn to play the piano as an adult than as a child).


Post Traumatic Stress Disorder

The activation of the autonomic nervous system (increased heart rate, blood pressure, respiration, etc) in response to danger is a normal, adaptive, and protective biological function. However, PTSD may occur when the ANS continues to engage once the threat is no longer present, leaving the body in an active state of arousal. This may occur if trauma is ongoing, as in repetitive abuse throughout childhood, or when a person is somehow unable to return to a sense of homeostasis and calm after exposure to trauma.

When the brain stores a memory within the limbic system instead of processing through to the cortex, it seems to just float in the hippocampus so that it can be easily accessed. To set the ANS in motion, the amygdala requires only a 10 to 20 percent overlap between a template for danger and a current sensory cue. This is why a seemingly innocuous cue (such as the smell of smoke for someone who has survived a fire) can send the body into fight, flight, or freeze mode. In some cases, a person may be responding to a cue that they are not consciously aware of, such as the slump of another person’s shoulders. Due to the mind-body connection, the amygdala may also interpret danger when the ANS is aroused for some other reason. For example, if heart rate was elevated during a traumatic event, later acceleration of the heart rate (while exercising) can signal danger to the amygdala.

From the standpoint of survival, it is preferable for the brain to over generalize signals of danger than to under generalize. But emotionally speaking, this can wreak havoc on a person’s life. Traumatized individuals may be more vulnerable to making false associations and interpreting danger in an environment where none exists. Due to plasticity, the more the autonomic nervous system is engaged, the more this pattern becomes ingrained. The more this pattern is ingrained, the more the ANS will be set off. This is the cycle of living with PTSD. In addition, an experience that sets off the body’s alarm response can alter the sensitivity of that alarm response. Over time, even non-sensory cues (remembering the event) can signal the amygdala and lead to an emotional response of fear.


Brain Plasticity – the good news

Although the brain has less plasticity as it ages and organizes, it can always be altered in significant ways. It is possible to re-train the Limbic System to become less reactive, meaning living with less fear and being triggered back to a trauma less often. Current research is finding that the most effective therapies for clearing trauma involve not emotionally reliving or re-experiencing the trauma but just the opposite. To help move traumatic memory out of the Limbic System, a person must be able to revisit the trauma without activating the Autonomic Nervous System. New methods for working with trauma effectively are constantly being discovered. Some of these methods may have a client talk through aspects of the trauma while keeping the Limbic System calm (clinical hypnosis, Rapid Resolution Therapy). Other methods, such as EMDR and EFT use eye movements or tapping on acupressure points to help the body release the trauma. It is believed that all effective trauma treatments work on a neurological level by creating new neural pathways within the brain. If you are dealing with an unresolved trauma, I encourage you to talk with your therapist about some of these and other techniques.

When traumatic memories get triggered and the ANS becomes activated, there are ways to help calm your system. Just focusing intently on the breath can be extremely helpful (please see the breathing exercises on the front page of this newsletter).  Activities that help to redirect you away from your emotions and towards purposeful relaxation of the body, such as yoga or Tai Chi, can also be effective. Sometimes doing a physical task can not only redirect your thoughts and feelings but also help to engage different parts of the cortex. This could be gardening, artwork, or something mechanical. Tasks that use both hands may be especially effective because they engage both sides of the brain. Many people with PTSD have found that practicing mindfulness and meditation can also reduce their symptoms. While it may be difficult to get into a meditative state once the ANS is activated, regular meditation is one great way to alter the limbic system’s level of reactivity.

In Conclusion

I hope that the information in this article has been informative and that in understanding the brain better, you will have greater compassion for the impact trauma has had on your life or the life of someone you know. If you find that reading about this topic is emotionally challenging, I encourage you to speak with your therapist. If you are not currently in therapy but are interested in starting this process, please consider contacting Karuna or any other therapist for an appointment.

National Center for Post Traumatic Stress Disorder

The National Institute of Mental Health



Rapid Resolution therapy

Book Recommendations

As a general rule, it is best for trauma survivors to avoid reading passages containing explicit description of other people’s trauma. Such material can unnecessarily trigger one’s own trauma experience. Be cautious, and feel free to step away from any reading that causes discomfort. If you believe that the material is worth learning about, please discuss it with your therapist or consider having a friend or partner read the information and relay the important aspects to you.  

Caring for the Child Within — A Manual for Grownups

By Jane Rowan

Outgrowing the Pain: A Book for and About Adults Abused As Children

by Eliana Gil (Author)

Outgrowing the Pain Together

by Eliana Gil (Author)

An Adult Child’s Guide to What’s ‘Normal’

by John C. Friel Ph.D. (Author), Linda D. Friel M.A. (Author)

The Sexual Healing Journey: A Guide for Survivors of Sexual Abuse (Revised Edition)

by Wendy Maltz (Author)

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