• Meghan McCarthy

Trauma & the Brain: Why Traumatic Memories are Different from the Rest

Even when your world seemingly stops, everyone else’s continues to move forward. This enigmatic quality allows for growth, second chances, and renewal.

 Photo by Francesco Gallarotti on Unsplash

Yet, when struggling, this quality of life makes it easy to feel  left behind and overwhelmed. 

Over fifty percent of the U.S. population goes through a traumatic experience. These are abrupt, dangerous events that endangers the life of you or those around you¹. Even worse, 7-8% of men and women suffer from PTSD, or post traumatic stress disorder².

Symptoms following traumatic experiences include anxiety, flashbacks, and even shame or guilt. Common treatments range from cognitive therapies to prolonged exposure, eye movement desensitization, and medication. 

The juxtaposition of trauma is that talking about the experience is vital to recovery. But, for some, it feels impossible to talk about.

If you relate to this statement, you aren’t alone. The reason being: trauma changes the brain’s wiring. Neurologically, it affects the way memory creation and processing. Trauma impairs the brain’s anatomical structure, and even changes chemical activity.

Types of Traumatic Memories

There are many different types of memories. But, memory formation is a distinct, three step process³. First, sensory information is received and translated into information our brain can analyze. Then, this information is sorted, processed, and sent for long term memory. The test of memory strength is in the last step, and occurs when a memory is recalled at a later time.

Photo by Debby Hudson on Unsplash

Explicit memories are ones that have context and perspective. The hippocampus processes explicit memories. This area of the brain creates memories with chronology and perspective. Under normal processing, explicit memories are the ones we consciously recall

Implicit memories are based purely on sensory experiences. The amygdala creates this type of memory. They are unconscious, and are impossible to verbalize as a result. Examples include our ability to perform daily tasks without thinking about it. For those suffering trauma, implicit memories can also be sensory associations and triggers.

One common symptom of trauma are intrusive memories. Intrusive memories can come out of nowhere. They include images, sensory experiences, and are often labelled as a ‘flashback.’. This type of memory can alter reality. They can cause a person to feel as if they are currently re-experiencing trauma. They also lack context. Even if a person knows they survived trauma, intrusive memories prompt fear

Opposingly, some traumatic memories are hard to retrieve. Often called ‘hidden memories,’ the brain can block recall of traumatic events in occasional amnesia

Trauma changes the way the brain processes memories. It's why traumatic experiences are ingrained in our memory, but difficult to talk about. There are a variety of traumatic memories and with this comes a variety of neurologic explanations.

The Neuroscience Behind Traumatic Memories

Traumatic memories are ironic. While they are easily remembered, they are often very poorly organized. 

When experiencing an intrusive memory, an individual often forgets key aspects of the experience. People with PTSD often forget the chronology of their trauma. Nicknamed ‘disjointed,’ such intrusive memories lack contextual information

One explanation for disjointed memories is limbic dysfunction. The limbic system is a group of brain regions that regulate emotions and memories. Two important regions in this system are the hippocampus and amygdala.

As explained earlier, the hippocampus handles explicit memories. The amygdala creates implicit ones. During traumatic experiences, the brain’s stress response is put into action. A key player in this is the hypothalamic pituitary adrenal axis (HPA). After 10 seconds of stress, the body activates HPA. When you sweat, have a sudden burst of energy, or even feel your heart pounding, it’s because of HPA. HPA releases stress hormones such as adrenaline, cortisol and norepinephrine.

These chemicals impair hippocampal function, and explain the poor organization of intrusive memories.  Initially, adrenaline causes the hippocampus to ‘super-encode’ moments of trauma. As cortisol and norepinephrine are released, the hippocampus then becomes suppressed¹⁰. The opposite happens in the amygdala, which becomes hyper activated during stress.

As a result, trauma creates a dysfunctional limbic system. There are many implications to this. First, it’s the reason why intrusive memories are often inaccurate or incomplete. Your hippocampus is able to store the first moments of trauma, but not the rest. This completely changes the consolidation phase of memory creation. The hippocampus is unable to integrate memory into perceptual areas of the brain. This causes disjointed memories that lack autobiographical context¹¹. ¹²

Trauma leaves the construction of memories unfinished.

[Left] Photo by Milivoj Kuhar on Unsplash [Right] Photo by Christopher Burns on Unsplash

It also explains why traumatic experiences are so hard to talk about. The amygdala creates unconscious memories, and is highly activated during trauma. These kinds of memories are literally impossible to verbalize¹².

Trauma alters the brain’s anatomy and physiology...

Recent studies have used MRIs to study limbic structures and trauma. Neuroimaging has shown that PTSD patients have significant bilateral hippocampal volume reduction. This means that both sides of their hippocampus are smaller than the average persons. 

Studies found that PTSD patients had a 7.1% reduction in hippocampal volume¹³

Functional MRIs have also shown that overactivation of the medial prefrontal cortex. This area of the brain influences the amygdala, and may contribute to hyperactivation. 

One biomarker for brain health is N-Acetylaspartate (NAA). NAA is an amino acid and indicator of neuronal health. People suffering trauma may have higher NAA levels in their hippocampal region. This indicates neuronal death and dysfunction.

GABA and Hidden Memories

Photo by Parker Johnson on Unsplash

Emotional memories are often the longest lasting. But, that doesn’t mean they are easy to talk about or remember.

Hidden memories are ones our brain blocks. They are hard to access, and are a reality many PTSD patients struggle with. 

A recent Northwestern study ties hidden memories to extra-synaptic GABA receptors¹⁴. GABA and glutamate are two neurotransmitters that work together in memory formation. Glutamate works to help memory storage. It’s goal is simple: create pathways that are easy to remember. 

Think of glutamate like a small child. It’s easily excitable, and often overactive. Regular, synaptic GABA is like glutamate’s older sibling. It calms glutamate down so that we don’t store unnecessary information.

Extra-synaptic GABA receptors have been found to work independent of glutamate. Researchers found that this special form of GABA works to create an ideal brain environment. After a traumatic experience, extra-synaptic GABA makes the painful memory as inaccessible as possible¹⁵.

Extra-synaptic GABA receptors have been found to work independent of glutamate. Researchers found that this special form of GABA works to create an ideal brain environment. After a traumatic experience, extra-synaptic GABA makes the painful memory as inaccessible as possible¹⁶.

Key Trauma Takeaways

The brain processes trauma uniquely. Trauma suppresses the hippocampus, overuses the amygdala, and changes hormone levels. This creates disorganized, but highly emotional memories. This dysfunction also makes trauma hard to talk about. 

Hopefully, this article helps put some pain into perspective. 

You aren’t at fault for your brain’s response to such stress. If you’ve suffered from a traumatic experience, remember that you aren’t alone.


  1. PTSD, N. (2013, August 15). VA.gov: Veterans Affairs. Retrieved August 03, 2020, from https://www.ptsd.va.gov/

  2. Ibid 

  3. How Memories Are Made: Stages of Memory Formation. (n.d.). Retrieved August 03, 2020, from https://lesley.edu/article/stages-of-memory

  4. Acheson, D. T., Gresack, J. E., & Risbrough, V. B. (2012). Hippocampal dysfunction effects on context memory: possible etiology for posttraumatic stress disorder. Neuropharmacology, 62(2), 674–685. https://doi.org/10.1016/j.neuropharm.2011.04.029

  5. Government of Canada, D. (2019, March 26). The Impact of Trauma on Adult Sexual Assault Victims. Retrieved August 03, 2020, from https://www.justice.gc.ca/eng/rp-pr/jr/trauma/p4.html

  6. Zimmermann, K. (2014, February 13). Implicit Memory: Definition and Examples. Retrieved August 03, 2020, from https://www.livescience.com/43353-implicit-memory.html

  7. Ehlers A. (2010). Understanding and Treating Unwanted Trauma Memories in Posttraumatic Stress Disorder. Zeitschrift fur Psychologie, 218(2), 141–145. https://doi.org/10.1027/0044-3409/a000021

  8. BOWER, G., & SIVERS, H. (1998). Cognitive impact of traumatic events. Development and Psychopathology,10(4), 625-653. doi:10.1017/S0954579498001795

  9. Ibid 

  10. Neurosci. (2014, June 04). Know your brain: HPA axis. Retrieved July 01, 2020, from https://www.neuroscientificallychallenged.com/blog/2014/5/31/what-is-the-hpa-axis

  11. Ibid 

  12. van Marle H. (2015). PTSD as a memory disorder. European Journal of Psychotraumatology, 6, 10.3402/ejpt.v6.27633. https://doi.org/10.3402/ejpt.v6.27633

  13. Ibid 

  14. Ibid 

  15. Vladimir Jovasevic, Kevin A Corcoran, Katherine Leaderbrand, Naoki Yamawaki, Anita L Guedea, Helen J Chen, Gordon M G Shepherd, Jelena Radulovic. GABAergic mechanisms regulated by miR-33 encode state-dependent fear. Nature Neuroscience, 2015; DOI: 10.1038/nn.4084

  16. Northwestern University. (2015, August 17). How traumatic memories hide in the brain, and how to retrieve them: Special brain mechanism discovered to store stress-related, unconscious memories. ScienceDaily. Retrieved August 2, 2020 from www.sciencedaily.com/releases/2015/08/150817132325.htm

  17. Ibid

  18. VAN DER KOLK, B.A. (1998), Trauma and memory. Psychiatry and Clinical Neurosciences, 52: S52-S64. doi:10.1046/j.1440-1819.1998.0520s5S97.x