A new rat study finds that post-traumatic stress disorder (PTSD) can develop even without explicit memory of an earlier trauma.
Researchers at the University of Albany and the University of California, Los Angeles note there are case reports of people who have experienced terrible life events that resulted in brain damage, some of whom developed syndromes similar to PTSD even though they had no recollection of the event.
These reports suggest that explicit memory — the type of memory that can be voluntarily recalled from prior experience — may not be a requirement for PTSD, whereas other forms of learning, such as fear conditioning, may be required, according to the researchers.
To test this hypothesis, Andrew Poulos, Ph.D., and his colleagues conducted a study designed to answer one question: If traumatic early life memories are lost, what persists of this experience?
In the laboratory, the researchers exposed juvenile rats to a single session of unpredictable stress. When the rats were adults, the researchers tested them for their memory of the event and also measured their fear response.
“We found that our rodents, which failed to remember the environment in which they were traumatized, showed a persistent increase in anxiety-related behavior and increased learning of new fear situations,” Poulos said. “These heightened levels of fear and anxiety corresponded with drastic changes in the daily rhythms of the circulating hormone corticosterone.”
Corticosterone is a hormone that, in part, regulates the body’s stress response. The researchers found that within the amygdala, a brain region crucial for the learning of fear, levels of a receptor for corticosterone were also increased.
“Future experiments in our laboratory will allow us to determine if this increase in glucocorticoid receptors within the amygdala and/or aberrant hormone levels sets up the organism for increased fear and anxiety,” Poulos said.
The findings indicate that not remembering a traumatic event does not stop an animal — or person — from experiencing some of the negative consequences of the trauma, such as anxiety and heightened fear, the researchers stated.
“These data highlight the importance of the many ways in which the brain processes traumatic experiences,” said Dr. John Krystal, editor of Biological Psychiatry, which published the study.
“Psychotherapy tends to focus heavily on the articulation of trauma memories. However, the current study highlights that these explicit memories may not represent all brain processes that drive distress and disability.”
“In other words, there may be a mismatch between what people think and how they feel about their traumatic experiences. Thus, there may be role in treatment for measuring other dimensions of response, such as physiologic arousal, through which some of these other forms of learning are expressed.”
Source: Biological Psychiatry