August 16, 2014
Explicit Memory Of Childhood Trauma Not Required For Development Of PTSD
redOrbit Staff & Wire Reports - Your Universe Online
Adults can develop post-traumatic stress disorder (PTSD) in response to an early-childhood event, even if they have no explicit memory of that trauma, claim the authors of a study appearing in Friday’s edition of the journal Biological Psychiatry.According to the University at Albany and the University of California, Los Angeles (UCLA) scientists behind the new research, there are many different types of memory, and that only some types are required for PTSD to develop. In fact, they said that there have even been case reports of individuals who have experienced events resulting in brain damage who went on to develop PTSD-like symptoms despite having no recollection of the incident itself.
Those case reports suggest that explicit memory may not be an absolute prerequisite for PTSD, the study authors explained. In order to test this hypothesis, Dr. Andrew Poulos of the UCLA Brain Research Institute and his colleagues devised a study to examine what parts of a traumatic early life experience remains if the memory is lost.
The experiment required exposing juvenile rodents to one session of unpredictable stress in the form of sudden, inescapable footshocks when they were just 19 days old. Later, when the creatures reached adulthood, the investigators tested them for memory of the incident and evaluated their fear response.
“Early trauma exposed rats displayed stereotypic footshock reactivity, yet by adulthood, hippocampus-dependent contextual fear-related memory was absent,” the authors wrote. “However, adult rats showed sensitized fear learning, aberrant basal circadian fluctuations of corticosterone, increased amygdalar glucocorticoid receptors, decreased time spent in the open arm of an elevated plus maze, and an odor aversion associated with early-life footshocks.”
In other words, as Poulos explained in a statement, his team found that the rodents “failed to remember the environment in which they were traumatized” but nonetheless continued to demonstrate “a persistent increase in anxiety related behavior and increased learning of new fear situations. 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 is partially responsible for regulating the body’s response to stress, and the research also revealed that levels of a receptor for this hormone increased in the amygdala, a region of the brain essential to the learning of fear. Poulos said that future research on this subject will allow them to determine if the increase in both corticosterone and the receptors prepares the organism for increased anxiety levels.
The combination of the research team's findings indicate that failure to remember a specific traumatic event does not necessarily preclude an organism from experiencing some of the negative consequences of such an occurrence, including elevated anxiety levels and a heightened sense of fear. They concluded that symptoms and neuropathology associated with human PTSD is possible, even when there is no explicit memory of the early trauma.
“These data highlight the importance of the many ways in which the brain processes traumatic experiences. Psychotherapy tends to focus heavily on the articulation of trauma memories,” said Dr. John Krystal, Editor of Biological Psychiatry. “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,” he added.