Category Archives: neurobiology

>Neurobiological responses to trauma and its memory

>The limbic system acts as the emotional thermometer which reacts environmental stimuli to assess whether it rewards or threats the individual. This system is made up of several regions in the brain including the amygdala, hippocampus,hypothalamus  and the frontal cortex. The amygdala and hippocampus are the two parts of the brain are essentially involved in response to, and memory of, traumatic events (See van der Kolk 1994, Nadel & Jacobs 1996, Levine1997).  The amygdala regulates regulates emotion and the hippocampus attaches emotional significance to experiences. Other parts of the limbic system regulates biological needs though the hypothalamus and the frontal cortex is responsible conscious thinking and emotions.

The Limbic System responds to extreme traumatic threat, in part, by releasing the stress hormones cortisol and adrenaline. This prepares the body for fight or flight. Th Sympathetic Nervous Systems prepares the body  through increasing respiration and heart rate to provide more oxygen, sending blood away from the skin and into the muscles for quick movement. In certain 
circumstances however, the Limbic system can simultaneously release hormones to activate the Parasympargetic Nervous System and a state of freezing can result (Gallup 1977, Levine1997). These circumstances are when there is not time or strength to fight and death may be imminent or when the traumatic threat is prolonged.. In this freezing state, the individual feels no pain enters an altered reality where time slows down. This is a form of dissociation which could have evolved in animals to contribute to a the chances of survival as the attacker (i.e. a cat) would lose interest in a stiffened prey (i.e. a lifeless mouse) These nervous system responses – fight, flight and freeze – are survival reflexes
There is growing belief that the amygdala is involved in storing these highly charged emotionial states. The other part of the brain, the hippocampus stores memory in a contextual form. This includes placing past events in its rightful place. However it is believed that when traumatic events happens, the hippocampus is supress and the temporal timestamp function of the hippocampus is prevented from happening. The traumatic memory becomes something that has the potential to seep into the present.

A term coined by Goleman (1997) is “Amygdala Hijack” which refers to the reactive tracking of a response through the amygdala rather than through the cortex. People with a history of trauma often have often have heightened reactivity and impulsivity around anger and fear. Life-threatening situations result in the permanent imprinting of the experience in the emotional circuits through the amygdala. Associated cues are stored through the declarative memory circuits involving the hippocampus which captures the emotional experience of the trauma.  These associated cues  can trigger the emotional memory of trauma thus bringing it to conscious awareness. For instance, a person who has been traumatised in war zone situations may be triggered by everyday explosive sounds such of a car tyre bursting. The sounds could trigger flashback with images and emotional reactions such as fear.

In psychodymanic theory, Bohleber(2007) aruges that the intensive exciatation increases the remberance of key features of the event atlough the unconnected details may not be. He argues that the ego has to be able to mantain the its observational function wherease in severe trauma this function breaks down. Memory can become fragemented.  With traumatic memories, the present can only perceive and structure the past in a limited way. When traumatic events are retained, the facts not the psychic reality of the inner experience are remembered.

With this limited evidence what I begin to see is the argument that storage and recall of traumatic memories are perceived to be different than the normal memories both in terms of neurobiological and psychological processes.