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The Neurobiology of Psychological Trauma and Posttraumatic Stress Disorder

The brain is one of the largest and most complex organs in the human body. It is made up of more than 100 billion nerves that communicate in trillions of synapses. The brain is the command center for the human nervous system. As a response to perceived threat, the brain’s sympathetic nervous system promotes the “fight or flight” response. When the threat is over, the parasympathetic nervous system puts a break and promotes “rest and digest”. These systems can become dysregulated after psychological trauma and in individuals who suffer from post-traumatic stress disorder (PTSD).

What is PTSD? According to the Substance Abuse and Mental Health Services Administration psychological trauma can result from experiencing an event, series of events, or set of circumstances that are physically or emotionally harmful or life threatening and that have lasting adverse effects in the individual’s functioning and mental, physical, social, emotional, or spiritual well-being.

Understanding the Neurobiology of Trauma With repeated stress, physical changes in the brain and hormonal imbalances can occur. These are partly the result of neurobiological changes, including the recruitment the hypothalamic-pituitary-adrenal (HPA) axis (Iacona & Johnson, 2018). The HPA axis is the central coordinators in the neuroendocrine stress response systems.

These are the steps of the HPA axis during a stressful event:

  1. The hypothalamus releases corticotropin releasing hormone (CRH)

  2. The anterior pituitary releases adenocorticotropic hormone (ACTH)

  3. ACTH then stimulates the adrenal cortex to release cortisol (the stress hormone).

  4. Cortisol increases body energy, suppresses immune system and suppresses inflammatory response.

  5. As the body senses the cortisol levels increasing and stress levels decrease, the hypothalamus will stop releasing CRH and the body returns to normal. This is called negative feedback

The problem with exposure to trauma is that this HPA axis is being constantly activated. This results in consistently high levels of stress hormones, and chronically affects the immune and inflammatory processes of the body.

Under normal conditions people react to a threat with a temporary increase in their stress hormones, which then dissipate after the threat is over and the body returns to normal. In traumatized people, it takes much longer for the stress hormones to return to normal and spike quickly and disproportionately. Elevated levels of stress hormones can have negative effects on memory and attention, irritability, and sleep disorders. They also contribute to many health issues. After trauma the world is experience with a different nervous system. Unbearable physiological reactions can result in a whole range of physical symptoms including fibromyalgia, chronic fatigue, and other autoimmune disease (Van der Kolk, 2015).

How trauma affects different regions of the brain

In patients with PTSD, three characteristic changes in brain structure and function have been identified:


  • Involved in the assessment of threat-related stimuli

  • Necessary for the process of fear

  • If the amygdala sense threat, it sends messages to recruit stress hormones by activating sympathetic nervous system.

  • The release of cortisol and adrenaline which increases heart rate, blood pressure, and breathing rate (it activates fight or flight)

In patients with PTSD, the amygdala shows increased response to general emotional stimuli, even if the stimulus is not associated with trauma.

Medial Prefrontal Cortex

  • Involved in the extinction of fear

  • Enables a person to see what is going on, predict what will happen, and make a conscious choice.

  • Regulate attention and awareness

  • Planning and anticipation

  • Sense of time and context

  • Inhibits inappropriate actions

  • Empathetic understanding

In patients with PTSD, this region of the brain is smaller and there is decreased activity. These patients may exhibit inappropriate fear responses and might be more impulsive.


  • Control of stress responses

  • Emotional encoding of memories

PTSD patients show reduced activity of hippocampus and struggle with dissociation, depression, and recollection of emotional memories.

Consequences of affected brain regions due to PTSD


  • Permanent alert

  • Increased startle

  • Poor sleep

  • Irritable

As a result of hyperarousal, people with PTSD can get emotionally triggered by anything that resembles the original trauma. They are frequently on edge and may also have difficulty sleeping or wake up in the middle of the night.


  • Feel powerless,

  • They might escape their situation not physically, but by altering their state of consciousness.

  • State of detached calmness (numbing) and dissociation.

  • Try to keep traumatic memories out of normal consciousness

These symptoms also affect anticipation and planning for the future to avoid any situation reminiscent of the past trauma. These people don't look for or accept new opportunities for successful coping that might mitigate the effect of the traumatic experience. These symptoms affect the quality of life and prolong the effects of trauma.


  • Reexperiencing/relieving the event as if it was still happening in the present.

  • They cannot go on with their lives because the trauma repeatedly interrupts.

The traumatic event becomes encoded in an abnormal form in memory (Herman 1997) which come spontaneously into consciousness awake or asleep. When high levels of adrenaline and other stress hormones are circulating, the memory becomes imprinted deep in the brain. They relive their trauma not only in their dreams and memories but also in their actions. In the attempt of undoing a traumatic moment, a survivor might put themselves in a risky situation.


  • Splitting and Isolation of memory imprints

  • Depersonalization- feeling as if the world is not real

  • Derealization- feeling as if the self is not real

These patients do not feel like themselves, struggle with monitoring threat, and also struggle with the ability to name and express their feelings. They feel a disconnection between themselves and their body.

Healing from Trauma

It is important to know that it is possible that the brain can recover from trauma! Whether they happened recently or a long time ago. There are many resources for different types of trauma. Some of these include but are not limited to:

Curious to learn more about the neurobiology of trauma?

You can click on the following links to learn in more depth about hot trauma can affect the brain, memories, behavior, and physiological responses.

References: Herman, J. L. (2015). Trauma and recovery: The aftermath of violence; from domestic abuse to political terror. New York: Basic Books.

Sherin, J. E., & Nemeroff, C. B. (2011). Post-traumatic stress disorder: the neurobiological impact of psychological trauma. Dialogues in clinical neuroscience, 13(3), 263–278.

Shin, L. M., Rauch, S. L., & Pitman, R. K. (2006). Amygdala, Medial Prefrontal Cortex, and Hippocampal Function in PTSD. Annals of the New York Academy of Sciences, 1071(1), 67-79. doi:10.1196/annals.1364.007

Van der Kolk, B. (2015). The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma by Bessel van der Kolk, MD | Key Takeaways, Analysis & Review. New York, New York: Penguin books.

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