In every human being, the brain is the control center and driving force for the simplest and most complex of tasks. The intricacies of this organ are so vast that there are so many unknown biological and conceptual facets that we, as a human species, don’t even know. This article will focus on one specific aspect of the brain: memory; and how trauma affects it.
What brain structures are responsible for memory?
While the brain structures responsible for memory consolidation, encoding, storage, and retrieval are ubiquitous, the two main structures that this article will discuss are the hippocampus and the amygdala, which are both parts of the larger limbic system. Without using too much psychological and biological jargon, the hippocampus plays a
primary role in memory consolidation and has to do with explicit memories — those that we consciously make and remember. The amygdala attaches emotional significance to memories and is a major component of fear processing. The amygdala is also responsible for activating the Fight, Flight, or Freeze response to fearful stimuli.
Fight, Flight, or Freeze
Responses to threat can trigger multiple physical and physiological responses. To list a few that may occur in the fight or flight response; heart rate may increase, pupils may dilate, dry mouth may occur, and perspiration may increase. In the freeze response, the body tries to counteract the flood of stress hormones released, thus leading to slowed responses such as slowed heart rate and breathing. These responses are automatic survival mechanisms, and cannot be stopped or controlled consciously.
Traumatic experience and multiple exposures to fearful situations would trigger these bodily responses. As such, studies have shown that abuse survivors and victims of long-term trauma have down-regulation of stress hormone receptors in the hippocampus, and both the hippocampus and amygdala structures are often smaller in the brains of these individuals (see more in our interview with Dr. Kate Harkness!). This can lead to problems recalling short term memories, emotional memories, and autobiographical memories through subconscious repression techniques.
Whenever a memory is created and encoded in the brain, there are both aspects of the explicit, conscious memory that the individual can recall, and the implicit, unconscious memory that is not in the individual’s control. In an experiment done on rats by LeDoux, researchers paired a jarring stimulus (i.e. a shock or loud sound), with a neutral stimulus (i.e. a photo of a flower, a music note). This process is called classical conditioning, and after enough rounds of exposure, the rat showed a fearful, unconscious fear response to neutral stimuli without a jarring stimulus present —they triggered the implicit memories in the brain. This experiment shows us how stress responses can unconsciously be elicited when an individual hears a sound, sees an object, or feels a surface that was relevant to them in a traumatic event.
"This experiment shows us how stress responses can unconsciously be elicited when an individual hears a sound, sees an object, or feels a surface that was relevant to them in a traumatic event."
Now, you may be asking yourself: “but how about those who remember a traumatic experience in fragmented pieces?” What you would be describing is a phenomenon known as ‘flashbulb memory’. When high levels of stress hormones are secreted, the hippocampus is flooded with stress hormones that impair its ability to encode the memory temporarily. Often, at the beginning of a stressful or traumatic event, the hippocampus works on overdrive, so this is why early moments are usually recalled quite accurately, but later lack contextual detail and can come in waves.
Though the extensive, widespread effects of trauma on memory and the brain are not fully known, and this article only covers a minor portion of its’ effects, hopefully, you gained more insight into just how and why these effects occur.
Written By: Daphna