Medical News Today: Can scientists learn to remove bad memories?

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.
photo of person turning away on dark background
Is it possible to ‘treat’ traumatic memories?

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.”

Medical News Today: Humans can learn new foreign words while asleep

Recent research reveals for the first time that people can learn new information while they are asleep.
woman asleep with book
Learning can also occur during sleep, new research shows.

Scientists already know that sleep consolidates learning of new information that we acquire during wakefulness.

Now, researchers at the University of Bern in Switzerland suggest that learning can also take place during deep, or slow-wave sleep.

In a study that features in the journal Current Biology, they show how associations with new foreign words can occur at certain phases of slow-wave sleep.

Much sleep research concerns the processes that stabilize and consolidate memories that form during periods of wakefulness.

There is now considerable evidence that replay during sleep strengthens memories and embeds them in the previously acquired knowledge store in the brain.

The study authors note that many deem it impossible that learning can take place during sleep because “sleep lacks the conscious awareness” and the necessary brain chemistry and activity.

In addition, studies that have examined sleep learning in humans have yielded conflicting results.

Learning during daytime naps

The researchers were intrigued by the question: If the sleep state strengthens a “memory trace” that forms during wakefulness, then why can’t the sleep state itself form a memory trace that endures into wakefulness?

Using electroencephalograms (EEGs), they recorded brainwave activity in 41 healthy male and female volunteers as they took a daytime nap and while they underwent subsequent memory tests.

During the nap, the volunteers also wore in-ear headphones through which the researchers played recordings of numerous verbal word pairs.

They devised each word pair so that one word was a familiar, native-language word while the other was a made-up “pseudoword.”

For example, they paired the word “house” with the pseudoword “tofer.” In another pair, the familiar word was “cork,” and the pseudoword was “aryl.”

After the nap, the volunteers underwent a test of their “sleep-formed associations.”

The test presented them with random samples of the pseudowords. At each presentation, they had to say whether the object the word described could fit inside a shoebox or not.

The results showed that the size classification of the pseudowords was better than chance if the “acoustic presentation of the second word of a pair during sleep repeatedly hit an ongoing slow-wave peak.”

Timing of encoding is key

Slow-wave, or deep sleep is the most beneficial stage for consolidating memories that form in the period of wakefulness that precedes it.

As the brain enters slow-wave sleep, its cells gradually synchronize their activity. They fall into a pattern that alternates every 0.5 seconds between brief periods of universal activity and inactivity. Periods of activity appear as peaks on EEGs.

The researchers found that the volunteers only encoded the association between a sleep-played, familiar, native-language word and its pseudoword under two conditions.

The first condition was repetition of the word pair, and the second condition was that the acoustic presentation of the second word had to coincide with an active phase of slow-wave sleep.

In other words, the volunteers were better able to correctly classify “tofer” as being too large to fit into a shoebox if they had heard the word pair “house-tofer” several times, and the second word had occurred while their brain cells were in an active phase of slow-wave sleep.

Co-first study author Marc Züst, Ph.D., says that they also observed that retrieval of sleep-learned words during the test coincided with activity in the hippocampus and language areas of the brain. The hippocampus plays a key role in memory and learning.

These are the same brain areas that are active when learning occurs during wakefulness.

These brain structures appear to mediate memory formation independently of the prevailing state of consciousness — unconscious during deep sleep, conscious during wakefulness.”

Marc Züst, Ph.D.

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2018-02-02 00:02:28.327

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