Can scientists learn to remove bad memories?
23 March, 2019
Traumatic memories can severely affect a person's quality of life when they become intrusive thoughts that lead to anxiety and continue to cause distress. For this reason, scientists are now looking into ways of weakening such memories and lessening their impact.
People who experience traumatic events may find their memories haunt them for a long time after the experience occurred.
Exposure to trauma can trigger numerous mental and emotional problems, including post-traumatic stress disorder (PTSD) and anxiety disorders, for example, phobias.
Ways of treating people who experience the long-term effects of trauma can include cognitive behavioral therapy (CBT) and other types of psychotherapy, as well as specific drug prescriptions to address symptoms of depression or anxiety.
However, increasingly, researchers are exploring ways of acting on the traumatic memories that cause an individual's long-term distress.
Such is the case with a team of scientists from five research institutions across three countries: Universidad Politécnica de Madrid, Universidad Complutense de Madrid, Reina Sofia–CIEN Foundation in Madrid, Spain, New York University, and the Radboud University Medical Centre in Nijmegen, the Netherlands.
These researchers have been looking into a novel way of weakening people's distressing memories and reducing their psychological impact.
Can we manipulate 'established' memories?
In a new study paper that appears in the journal Science Advances and whose first author is Ana Galarza Vallejo, the researchers write that "[a]n effective treatment for these disorders [related to trauma] should selectively decrease these intrusive, pathological memories."
At the same time, they note that the prevailing opinion in memory research has been that "established memories are relatively fixed" and, thus, cannot be easily modified. Yet, in their new study, the investigators show that acting on disturbing memories is, in fact, a clear possibility.
"[M]emories are initially labile and sensitive to interference by, e.g., electroconvulsive therapy, general anesthesia, or protein synthesis inhibition, but stabilize over time during a period of consolidation, after which memories were considered to be established and no longer sensitive to disruption or modification," the authors write.
However, the scientists observe that past research that researchers conducted using animal models suggested that reactivating an already established memory can, for a short time, make it "vulnerable" to external modifications.
Building on this existing evidence, they decided to work with a group of human participants, and test an intervention they based on administering the anesthetic propofol.
Well-timed sedative acts on bad memories
In the current study, Vallejo and colleagues recruited 50 healthy participants, in whom they first instilled unwanted memories by asking them to watch two narrated slideshows. Both of these slideshows featured negative emotional content about midway through.
To reactive the bad memories, the researchers called the participants back after 1 week, and showed them the first slide from one of the two presentations, asking them targeted questions.
Once the participants started recalling the unwanted memories, the investigators sedated them with propofol, the anesthetic whose potential in memory-manipulation the team wanted to assess.
Then, the researchers assigned the participants to one of two groups. Following on 24 hours after the propofol injection, the people in the first groups had to take a test evaluating their recall of the stories in each of the two slideshows — both the one which they had had to remember before sedation and the one which they were not prompted to recall.
As for the participants in the second group, they took the same tests immediately after having received the propofol intervention.
The investigators found that 24 hours after its administration, propofol had effectively disrupted the reconsolidation of the bad memory that researchers had asked participants to recall.
Thus, while the individuals in the first group were still able to remember the negative memory they associated with the slideshow that they had not recalled before the sedation, their memory of the reactivated story was weaker.
Following these findings, Vallejo and team believe that they may have found a "relatively noninvasive" way of dimming traumatic memories and reducing their psychological impact.
"However," the researchers warn, "there is also evidence that altering parameters of the reactivation session, such as increasing duration, can destabilize remote memories," which would be an unwanted effect.
The scientists advise that it may be useful, going forward, to monitor participants' brain activity as they receive the treatment to assess what the best dosage might be. They conclude:
"The administration of propofol with simultaneous recording of the electroencephalogram may provide useful markers of the depth of sedation and loss of consciousness potentially predictive of efficacy of reconsolidation impairment across patients."
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