PTSD Can Develop Without Memory of Trauma
These flashbacks may be triggered by objects, words or situations in which people find themselves, or by their own thoughts and feelings. These can lead to “avoidance symptoms” as people attempt to steer clear of things that might trigger flashbacks or negative thoughts and feelings.
Memory of trauma seems to play an important role in these and other symptoms of PTSD. However, new findings from a cooperative study between the University at Albany and UCLA suggest that people who do not have explicit memories of a traumatic experience can still develop symptoms of PTSD.
Explicit memories, also called declarative memories, are memories than can be consciously and deliberately recalled and described. Humans also have implicit memories, alternately called procedural memories, which are skills and procedures that we can approach unconsciously. Implicit memory is sometimes colloquially referred to as “muscle memory,” and includes things like riding a bike or tying shoelaces.
The new study, published in Biological Psychiatry, found that rodents exposed to an incident of unpredictable stress when they were 19 days old (in the form of inescapable foot shocks) developed symptoms of PTSD even if they did not remember the event itself.
Cases in Humans
This is a phenomenon that has occurred in humans, but it is not well understood. There are documented cases of individuals with brain damage from a traumatic event who develop PTSD even though they cannot remember the event that traumatized them. There are also known cases of children developing PTSD symptoms as adults following traumatic events in their childhoods that they do not explicitly recall.
The researchers hoped to use their rodent studies to confirm this phenomenon, and, if the research did confirm it, to discover what remains from these experiences to trigger PTSD, if not explicit memories.
The rodents were tested for memory of the previous traumatic event as well as their sensitivity to fear learning. They found that rats with no explicit memory still displayed aversion to things associated with their previous traumatic experience, such as certain odors and areas of an elevated maze. When exposed to these triggers, they displayed heightened fear and anxiety.
The researchers also examined the way that the rodents’ brain chemistry responded to these situations, and they found that sharp increases in the daily levels of corticosterone corresponded with increased anxiety and fear. The researchers will use future studies to test the hypothesis that these increased levels of cortisosterone (a hormone that regulates the body’s stress response) is the underling mechanism for sensitive fear learning and anxiety in the absence of explicit memories.
Treatment May Need to Go Beyond Confronting Explicit Memories
In addition, the research suggests that brain processes other than explicit memory are present even when patients do remember a stressful or traumatic event. Traditional psychotherapy tends to focus on explicit memories, but there may be other elements of traumatic experiences that should be addressed for complete recovery.
These rodent experiments suggest that traumatic experiences trigger changes in neuropathology that affect how the brain reacts chemically to fear situations, at least when the trauma occurs during a period of development for the hippocampus. Exactly how these neurobiological changes might be addressed during treatment programs for PTSD is another topic for future research and discussion.