Effects of Trauma Do not Require Specific Memories

Rats that don’t remember trauma still show behavior and brain changes.

Posted Oct 06, 2014

Post Traumatic Stress Disorder (PTSD) is generally a problem of not being able to forget, rather than not being able to remember.   Nevertheless, there has been ongoing debate regarding the question of whether traumatic experiences that are not remembered still can have long-lasting effects on behavior and can alter the body’s response to stress.  Not remembering is often thought to come from two main sources.  The first is due to someone being too young to be able to form specific or “declarative” memories of an event.  The second, and more controversial, mechanism regards “repressed memories” in which there is an active and protective brain process to exclude a memory or memories from consciousness.   Related to these issues is the question of how much benefit there is to bring these memories to consciousness in the course of therapy and treatment.

Into the fray is a new and provocative study from the well-regarded journal Biological Psychiatry.  The research involved rats when they were 19 days old, at time before their memory systems are mature enough to make specific contextual memories.  The animals were given unpredictable and unescapable footshocks.  Two months later, these rats were tested for how quickly they acquired fear, how they explored new situations, and what their brains looked like by way of their density of receptors for key stress hormones and proteins in a part of the brain called the amygdala that is important in fear processing.

When rats were brought back to the footshock environment, they showed no behavior suggesting that they remembered the event (although it had been shown in previous experiments that older rats definitely do).  Yet despite this lack of memory, the shocked rats in other tests became fearful very quickly, had an aversion to a smell that had been paired with the footshocks, and looked anxious and hesitant when put in a new situation (an elevated maze).  In terms of brain activity, these rats now had an abnormal secretion pattern of the stress hormone cortisol and changes in the density of certain receptors in the amygdala.   

The authors concluded that, at least in animals, trauma suffered early in life and before declarative memory processes are online can still result in behavioral and neurobiological effects similar to changes found in people who suffer from PTSD.

To the extent that one can trust the leap from an animal study to humans, this is an important study showing pretty strong evidence that the effects of trauma do not require the presence of specific memories.  At the same, in seeing how this study has been covered in the press at times, it is also critical to “remember” that the study really can say nothing about more controversial topics such as 1) whether or not there is any gain in making such memories more accessible during treatment, or 2) the existence of an active process that works to remove certain memories from consciousness.  If anything, the fact that we see this phenomenon of forgotten memories having psychological and physiological effects in rodents suggests that a more active repression process certainly is not required for it to occur. 

Photo courtesy of David Castillo Dominici and freedigitalphotos.net

@copyright by David Rettew, MD


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