Trauma (and, more precisely, the stress that usually accompanies trauma) has identifiable effects on the hippocampus, impairing both the neuronal structure and the function of this brain region. As a direct consequence, stress (especially uncontrollable stressors) impairs various forms of memory. Experience of stress (through its impact on the hippocampus) causes stressful events to be recorded in a “fragmented” manner, with the elements of the event not woven into a coherent remembered episode. At the same time, emotion works (via the amygdala) to promote memory for the gist of an event, leading to well-encoded memories for the thematic content of an emotion event, but, again, without the coherent spatio-temporal framework needed to organize the memory (because this framework relies on hippocampal circuits disrupted by stress).
Let us first look at the four types of memory :
- Semantic – General knowledge and facts. If you were in a car accident, you would remember the colour of the other person’s car, the time of day it was, and that there was an ambulance team on site.
- Episodic – Autobiographical memory. If you were in a car accident, you would remember how the road looked as your spun out of control and the look on the other driver’s face as they ran into you.
- Emotional – Remembering feelings. If you were in a car accident, you would remember the fear you felt when you wondered if you were going to survive and the rage you felt when you found out the other driver was drunk.
- Procedural – Order of events. If you were in a car accident, you would remember the ambulance team got there first, then the police and the fire department.
When people experience a trauma, they may not remember the colour of the other person’s car from the accident or who arrived to the scene first. So what happens in the brain to make this so difficult? Let us look at how trauma affects your memory :
- Semantic – Controlled by the temporal lobe and inferior parietal cortex. PTSD has an impact on communication between the temporal and parietal regions of the brain. This can make certain parts of your memory like words or images not combine to make a cohesive semantic memory.
- Episodic – Controlled by the hippocampus. Constant stress may damage the hippocampus because of the hormone called cortisol that is released which can cause these memories to become a blur.
- Emotional – Controlled by the amygdala. After experiencing trauma, your amygdala can become overactive sending fear signals when there is no perceivable threat present. This is why many people experience flashbacks or relive events from triggers.
- Procedural – Controlled by the striatum. People who have PTSD have hyperactivity between the hippocampus and the stratum and the activity is very difficult to reduce which can lead to habit like responses to triggers.