Memory Reconsolidation and PTSD
June 2, 2014
PTSD has been called a disorder of sleep, which it certainly seems to be, disrupting both sleep onset and sleep maintenance. A recently published flow diagram for PTSD treatment indicates trazodone (for inducing sleep) and prazosin (for blocking nightmares) as the first medications to try. My own experience in treating PTSD supports this strategy.
However, at a deeper level, PTSD is a disorder of memory, in particular, a disorder of excessive remembering (or insufficient forgetting). Flashbacks and nightmares associated with PTSD reflect a failure to forget the trauma, which in some cases may have occurred as long as 30-50 or more years earlier.
While blocking nightmares with prazosin can be effective treatment for PTSD, the nightmares return promptly following missed doses of prazosin. We need a more permanent treatment for PTSD.
In an earlier blog (8/5/13) I reviewed basic concepts of memory formation. Here I provide additional details. Short-term memories are converted to long-term memories by a process referred to as “consolidation”, which typically occurs during sleep. The hippocampus is the main memory center of the brain. The amygdala assists the hippocampus in processing highly emotional memories, which are thought to be consolidated in the brain during rapid eye movement or REM sleep. Memories of events (episodic memories) that are not highly emotional are thought to be consolidated during non-REM sleep. Emotional memories are somehow flagged by the brain as being of high importance, and are usually easier to recall than memories that are not emotional.
In recent years there has been increasing interest in the process of memory “reconsolidation”. In the past it was believed that a long-term memory remained essentially unchanged following consolidation, while fading gradually over time. In fact, each time a memory is recalled, it is reconsolidated. The reconsolidation allows the memory to change, based on events that may have occurred since the original event. Elizabeth Loftus, a psychologist at the University of California, Irvine, has studied “false memories” that she induces into the consciousness of normal human subjects. As a result of her work, therapists are warned not to make suggestive statements to vulnerable clients (especially children) about traumatic things that might have happened in their past.
In the case of someone suffering from PTSD, the phenomenon of memory reconsolidation allows the therapist the opportunity of reducing or even eliminating the impact of a traumatic memory. The idea of erasing unwanted memories was the basis of a movie, Eternal Sunshine of the Spotless Mind, in which a couple (Jim Carrey and Kate Winslet), following their breakup, go to a fictional (i.e, “science fictional”) memory-erasing lab to have their memories of each other removed from their brains.
A recent article, “Partial Recall”, by Michael Spector in the New Yorker magazine (5/19/14) describes the memory reconsolidation studies of Daniela Schiller, a neuroscience researcher at Mount Sinai School of Medicine in New York, and the daughter of a Holocaust surviver, her father, currently living in Israel.
Dr. Schiller is interested in the possibility of blocking emotional posttrauma memories as a treatment for PTSD. Schiller and her colleagues recently published an article in Nature (1/7/10), describing a successful test of their methods (in normal subjects), which involved extinction of the fear response (a painful memory) to a mild electric shock to the wrist. The memory was objectively measured as an increase in skin conductance. Extinction was produced by updating fear memories with non-fearful information. The authors suggest that the method might be applicable to patients suffering from PTSD. People suffering from PTSD are susceptible to “triggers”, which remind them of their earlier trauma. Following exposure to a trigger, PTSD sufferers experience flashbacks (while awake) and/or nightmares (while asleep), which reproduce the actual sensory experiences of the trauma. In the normal sequence of events, a trigger causes a flashback, which is then reconsolidated during a subsequent REM sleep episode, resulting in a nightmare.
The nightmare revision procedure described in this website is designed to block (or alter) such trauma reconsolidation by changing the content of the nightmare prior to its occurrence. In this sense, the goal of nightmare revision (or imagery rehearsal therapy, IRT, as it is also called), is similar to the goal of Schiller and colleagues, though with different methodologies.
To block memory reconsolidation in a PTSD patient, Schiller and colleagues would presumably need to present a trigger and then block the resulting flashback, thereby eliminating the subsequent nightmare. The precise timing required for such an intervention seems a bit challenging.
Our intervention, dream revision, by changing the anticipated nightmare before it occurs, seems to be a more direct approach. Furthermore, dream revision has been shown to work, as we and others have described. Schiller and colleagues have not yet demonstrated the efficacy of their method in PTSD patients (though Dr. Schiller indicates she was motivated to do the experiment by her father’s apparent success in erasing or suppressing all of his Holocaust memories).
