Quirks of Memory

A Retrieval System Roundup

Can Unwanted Memories Be Undone?

Cuing negative or traumatic memories during sleep may have surprising benefits.

Are some things better off not being remembered? 

In the futuristic movie “The Eternal Sunshine of the Spotless Mind,” Jim Carrey’s character regrets launching the memory erasure process designed to erase his memories of his ex-girlfriend. He comes to realize during the erasure process that there are many happy memories in there that he wants to hang on to, even though the break up was tough. 

We are far from being able to erase something from memory as complex as a relationship with another person. As memory researchers are often quick to point out, memory does not work like a video recorder, so it’s not as simple as pressing rewind and sifting through old memories to pluck out everything containing a particular person. And, it may never be possible to eliminate memories for something so richly intertwined with other life events and personal knowledge as another person who was part of them. 

But what if what you want to eliminate is not a memory for a long and complex relationship with another person, but a particular memory for a unique traumatic event?

Not only does the capability already exist for preventing people from remembering specific events, but doing so is commonly practiced in some situations. Take, for example, surgeries and certain medical procedures. Amnesia drugs are regularly used in these situations to prevent the patient from having any memory of the procedure. In fact, amnesia is one of the major goals of general anesthesia.

When I was about to undergo a surgery years ago, I was discussing the various drugs that would be used with the anesthesiologist. When I asked why amnesia drugs were needed, he told me that it was so that if I woke up in surgery, I wouldn’t be traumatized by the memory of it. (A different anesthesiologist was more cynical: “It’s so that you don’t go on a talk show and talk about how you woke up during surgery if it happens” he said). In any case, amnesia drugs are commonly used to ensure that the person doesn't remember anything that happened during surgery.

And they seem to work. I found out from others that shortly after waking from anesthesia, I kept repeating the same question, “Did I get amnesia drugs?” over and over, even though I could not remember even asking it. Apparently, after getting the answer, moments later, I would ask it again, as if for the first time. It was a disconcerting feeling to think that I’d carried on conversations and had no memory of them--that I had to rely on others to tell me that I’d had the conversations. The way that I repeated the same question over and over is characteristic of hippocampal amnesics, making it seem likely that my hippocampus was temporarily knocked offline by the amnesia drugs, and this played a role in the amnesia that persisted shortly after the surgery. If I did wake up during surgery, I certainly wouldn’t recall it.

But amnesia drugs prevent memories from forming in the first place. What about when an event has already happened and the memory already had a chance to form? Can it be undone after the fact?

We may be on the verge of being able to undo memories after the fact. And, it may even be possible to do it without drugs.

In their recent article, "Fear not: Manipulating sleep might help you forget," Oudiette and colleagues review evidence that reminders of traumatic memories during sleep might help to diminish the memory (or at least it's negative, emotional effect). Hauner and colleagues (2013) trained people to associate certain pictures of faces with both a particular smell (such as mint) and an unpleasant electrical shock. The researchers measured fear reactions using skin conductance responses. As expected, people exhibited fear reactions to the face-odor pairs that had been previously associated with the shock. 

What is surprising is what happened when the researchers later presented the smells during sleep. As I’ve written previously, such sleep-cuing can enhance memory for visual information, even when smells are used as the cues. Initially, presenting the odor during sleep led to the same type of physical fear reaction during sleep (measured with skin responses) that occurred while awake. However, after many presentations of the odor (at 30 second intervals), the skin conductance reaction during sleep subsided. Later on while awake, the skin responses to the face/odor pairs that had been associated with electrical shock had also disappeared. It was as if the fearful reaction to the triggers had been extinguished by the repeated cuing with smells that took place during sleep.

The researchers suggest here that repeatedly cuing with the odor during sleep allowed for the formation of new, non-fearful connections in response to it (and its associated face) so that these potential triggers were no longer uniquely tied to a fearful experience. This fits an idea I mentioned here, "The more uniquely a cue around you (such as a sight, a sound or a smell) connects to one particular memory as opposed to many, the more likely it is to conjure up that memory."  Maybe repeatedly cuing a fearful memory during sleep allows for better integration of the triggers (i.e., the odor or the face) with other memories so that the triggers are not so tightly tied to the emotional reaction itself.

Though further research is needed, this research presents a first step toward potentially using sleep-reminders to alleviate problems associated with traumatic memories.

For more information on other ways of erasing memories and the ethical considerations in doing so, see here, here, here, and here.

Anne Cleary, Ph.D., is a professor at Colorado State University.


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