Fortunately with all the brain scans that are available today, there are some strong theories out there about how trauma changes the way the brain works.
Though no one knows for sure, it seems apparent that trauma changes the wiring in the brain. According to Earl Grey, PhD, normally when we take in information through our five senses, it reports to the center (the hippocampus) of our brain for processing. Then it is sent to the thalamus to decide where it needs to be stored. Eventually, from there, information is sent to the front of our brain (the prefrontal cortex) our brain’s filing cabinet. The prefrontal cortex acknowledges a past, present, and future time line. Events can be filed in chronological order. When something overwhelmingly upsetting happens to us, such as in the case of a trauma, the hippocampus becomes unable to handle it. The unprocessed information about the situation is still sent to the thalamus, but this time it is rejected and sent to the primitive brain or reptilian brain, via the hypothalamus basal ganglia, in the back of our heads. Here there is no acknowledgment of a past or future. Everything is happening in the present. The event, the emotions, body sensations and negative beliefs feel as if they are happening now. So we react with a flight, fight or freeze reaction to the upsetting situation. We want to run away, we stand and fight or we cannot move.
The situation does not get processed properly and we are stuck reliving it over and over. The upsetting event, the emotions and body sensations connected to that event and the negative cognitions that come out of this event all replay involuntarily in the primitive part of the brain. This can look like flashbacks, nightmares or other trauma symptoms that keep us stuck in the traumatic past.
The good news is that this circuit can be rerouted. We know that releasing the emotional connection to the event allows a new neural pathway to be created, from the back of the brain (primitive brain) to the front of the front of the brain (the prefrontal cortex), where the information (data/memory) can be stored in its proper chronological place in the past as is desired. Once this is done, the event is no longer emotionally connected in our brain. We remember it, but the memory will not create and recreate the intense emotional response in us. In other words, through reprocessing the trauma, we can rewire the miss-wired trauma brain.