The Neurobiology of Psychological Trauma

In this section we are still considering the neurobiology of trauma, rather than its longer-term consequence, Posttraumatic Stress Disorder. A person may have a traumatic experience, i.e., an experience that is potentially traumatizing, in that it is impactful enough to overwhelm the mind’s ability to cope with the experience. That person might suffer from trauma in the short term, but might not go on to develop PTSD. Psychiatry now labels the short term experience of trauma as Acute Stress Disorder.

If the traumatised person is given the right help as soon as possible, their shocked system might be able to recover and not develop PTSD. They will be helped to bring the implicitly stored memories of the experience to the surface for correct storage procedure into explicit memory, so that the event can be talked about and made sense of, and hopefully put into the past.

The brain science that relates to a potentially overwhelming experience

Brain anterior posterior

The brain is an organ designed to detect and analyze incoming stimuli and formulate appropriate responses to those stimuli. The goal of the brain as a data processing system is to maintain the organism (us) safely in our internal and external environment. This ranges from oxygen intake and temperature control to categorizing incoming information, to formulation of complex decisions about safety, communication and actions, to name a few.

The brain needs to regulate information, process it and act upon it. It needs to learn from experience and be able to decide which stimuli require action and which do not, in order to meet functional goals. The ability to comprehend (grasp and process) an event significantly affects whether that event will be experienced as traumatic.

The brain is divided into three sub-analyzers :

  • Brain stem and hypothalamus – regulation of internal homeostasis, ie, keeping the internal environment balanced and safe. Generally stable and less affected by experience.
  • Limbic system, including the hippocampus – maintaining balance between the internal world and external reality. Contains stable, internally focused circuitry and circuitry that can be modified by experience
  • Neocortex – analyzing and interacting with the external world. Most affected by environmental input and experience.
  • brain-basic_and_limbic


[Image:courtesy of The Brainwaves Center. ]

It would be expected then that trauma would affect the neocortex rather than innate (autonomic) systems like the brain-stem. That is true of normal stress responses, but traumatic stress overwhelms the whole system and affects all sub-systems of the brain structure.

Traumatised behaviour is NOT a simple exaggeration of the normal stress response. It is not simple conditioning. (Someone who has been conditioned will respond to the same stressor when confronted with it, and no others. Traumatised people in the process of developing PTSD are triggered by stimuli that have nothing to do with, but remind them, of the original trauma. )


Faced with a life-threatening, overwhelming or traumatic event, our primary focus is on

  • survival
  • self-protection.

Inability to ‘get out of harm’s way’ or extract oneself from the situation forces the system into

  • overdrive’ of adrenaline producing emotions:
    • fear,
    • shock,
    • confusion,
    • numbness
    • speechless terror.

The body’s ‘fight-or-flight’ mechanism is paralyzed when neither fight nor flight is possible. The body’s chemical system is overloaded and the ability to record the experience properly breaks down.

  • The hippocampus is temporarily shut down – because:
  • Adrenaline turns off hippocampal functioning
  • Cortisol shuts off explicit encoding
  • Both are Sympathetic system stress hormones.
  • The Hippocampus needs focused consciousness to function.

The amygdala is overwhelmed and unable to do its job of assigning significance to the incoming information for transfer to the hippocampus, which will record the events into short and long term, but not permanent, memory. [note: short term memory is only 15 to 30 seconds, long term is about 2 days, until the details deemed important are consolidated into permanent memory in the cortex.]

The brain’s natural ability to integrate experience has broken down, due to the flooding of stress hormones at the moment of the traumatic experience and the catastrophic response of the central nervous system.

Coping Styles during the event affects PTSD outcome

[note here that coping style is linked to how much CONTROL a person feels they have during the event] 

  • Problem-focussed coping versus dissociation, during traumatic event, reduces the chance of developing PTSD.
  • Dissociation during the event increases the likelihood of developing PTSD.
  • The longer the event lasts the more likely one is to develop PTSD.

What makes memory of the experience traumatic, is that those memories have been stored in separate and isolated parts of the brain. They are retrieved, usually by association and triggering, as isolated fragments, disconnected and chaotic. These are usually called ‘flashbacks’. Often the survivor is not even aware what the flashback is about, as there is often little autobiographical information attached.

The structures that are involved in integrative processes :

  • Parietal lobes – integrate information between cortical areas
  • Hippocampus – creates a cognitive map to categorize experience and connect it to other autobiographical information
  • Corpus callosum – facilitates transfer of information across hemispheres, integrating emotional and cognitive aspects of experience
  • Cingulate gyrus – amplifer and filter helping to integrate emotional and cognitive components of the mind
  • Dorsolateral frontal cortex – where sensations are ‘held in mind’ and compared with previous information to plan appropriate action.

[See The Brainwaves Center, ‘Your brain and what it does’, for a glossary of major brain areas and their functions.]

Different hemisphere processing of traumatic material 

Right hemisphere, most involved in traumatic experiencing : experiencing of global, non-verbal emotional communication (ie, tone of voice, facial expression etc.). Integrated with amygdala which assigns emotional significance to incoming stimuli and helps to regulate the autonomic responses to those stimuli. Extremely sensitive to emotional signals. Very little capacity to ‘think’ analytically or reason.

Left hemisphere, less active during traumatic experience : verbal communication, problem-solving, processes information in sequential, linier fashion, categorizes and labels incoming information.

Conclusion:  the function of left hemisphere is impeded during times of extreme emotional arousal. People with PTSD find it very hard to categorize their feelings or label their internal states. The experience of ‘dissociation’ is related to the decrease in left hemisphere activity, ‘space-time’ becomes disoriented, thinking is fuzzy, loss of clarity, logical thinking, etc.

Consolidation & Integration of traumatic experiences: during REM sleep, all humans play back events as part of the process of sorting, categorizing and storing the memories into appropriate cortical association areas, so that they can be recalled when needed. The back and forth, right to left eye movements indicate the processing of images from right to left hemisphere, across the corpus callosum. However, traumatic material is stored in implicit memory and unable to be categorized during REM sleep. When the trauma survivor continually experiences intrusive images and nightmares of past horrors, it may be the brain’s futile attempts to resolve and consolidate these blocked memories.

More on Trauma


What is Trauma?

The Role of Memory in Trauma


An Evolutionary Model of Response to Danger

The Brain’s “Information Processing System”

Further Resources and Reading (Trauma)

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