An Evolutionary Model of Response to Danger


Evidence for an evolutionary model of traumatic response to life-threatening events


Emotional arousal leads to deeper impact of an event. When highly aroused, the brain releases catecholamines (epinephrine and norepinephrine) from the autonomic nervous system (sympathetic system) and the endocrine system. This creates arousal of the nervous system and the reactivation of whatever thoughts are in play at the moment of the experience. This release of hormones during the event has the effect of recycling the experience and the events leading up to it, in the mind of the person having the experience.

This recycling and rehearsal of the event in the mind and emotions of the victim enhances his/her learning from the experience, particularly learning the specific messages encoded into memory. The immediate physiological arousal only lasts a few minutes, but leads the mind to return to the experience again and again over the following days or months, especially when triggered by associational cues.

This biological system has an evolutionary advantage, as it forces the individual to learn from life-threatening experience and to be hypervigilant to any recurrances, and on guard against future threat. In ancient times this would have increased the chances of survival. However, these earlier forms of life-threatening situations would have been more likely to involve the opportunity for fight or flight.

The kinds of trauma leading to PTSD are ones where the victim is trapped and unable to respond in an adaptive way. When this happens, the flight-or-fight system is overwhelmed, and the memory system malfunctions. The explicit memory needed to learn from the experience cannot be encoded, as the functioning of the hippocampus is blocked by the overarousal of the amygdala. The amygdala, part of the limbic system, plays an important role in assigning value and importance to an experience and helping the hippocampus to encode it into explicit memory.

However, explicit encoding requires focused attention. During an inescapable traumatic event, the victim frequently focuses attention on a non-traumatic or neutral part of the environment, or dissociates mentally in order to ‘escape’. This produces ‘divided-attention’, which prevents explicit memory encoding. Instead, the event is encoded implicitly, which means it is not available to normal awareness.


Emotionally arousing experiences are more readily remembered later on. The task of the amygdala is to assign emotional significance of events and pass these ‘conclusions’ on to the hippocampus. Although the exact mechanism is not yet understood, it seems clear that this relationship between amygdala and hippocampus breaks down under extreme stress, and the emotional impact is re-routed into the implicit memory system. The implicit memory system is connected to the deepest levels of our emotional memory, which were laid down in early childhood. This is why a smell can suddenly bring back a memory of intense emotion, often without any autobiographical detail attached. It also explains why a seemingly ‘low-level’ or ‘small-T’ event can lead to a person developing PTSD – because they have a prior trauma further down in the memory tree. The adult experience of low-level trauma links to the earlier experience and the total effect can amplify the stress response towards full-blown PTSD.

To understand the impact of trauma, it is essential to understand the importance of the connection between emotion and memory at the most fundamental level of the brain’s system.

The way out of traumatic damage is to repair the link between our memory and our emotions. This is not an easy task, however, and requires COURAGE.

Memories from a traumatic event that have been stored in implicit memory come back as intrusive elements and flashbacks :

  • Impulse to flee (behavioural memory)
  • Emotional reactions (emotional memory)
  • Intrusive images     (sensory memory)
  • Bodily sensations     (sensory memory)

Implicit memory recall feels as if it is happening NOW. This is the essence of implicit memory. It is the NOWness of the experience that makes it so difficult to work with. The trauma survivor has to learn to use their frontal cortex (executive or higher brain) to override the sensation that this is about the present, and re-interpret it as memory of past events.


More on Trauma


What is Trauma?

The Role of Memory in Trauma

The Neurobiology of Psychological Trauma


The Brain’s “Information Processing System”

Further Resources and Reading (Trauma)


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