Memory Special: Can You Choose What to Forget?

The title of this post is identical to the title of a feature article by Penny Sarchet in the 27 Oct 2018 issue of the “New Scientist.” Here’s how to choose what memories to forget. It is commonly thought that we can actively strengthen memories, whereas forgetting is a passive process. We now have discovered that forgetting can be intentional.

Jeremy Manning of Dartmouth College has found that just telling people to “push thought out of their head” is enough to make them forget lists of words they have learned to associate with particular cues. He says, “We don’t know how, but some people seem to know how to do it. Justin Hulbert at Bard College says that suppression has been linked to decreased activity in the hippocampus, so we may be unknowingly reducing our hippocampal activity by focusing on the present.

Of course, he is speaking of words learned in an experiment. Memories from private lives can be an entirely different matter. Post traumatic stress disorder (PTSD) involves intrusive memories that keep coming back—often suddenly and unexpectedly. Studies have found that people with this condition are less able to suppress memories, even those unrelated to traumatic incidents.

There are other approaches to forgetting, including what are known as cognitive vaccines: interventions that can “inoculate” the brain agains the onset of PTSD symptoms if administered soon after trauma.

Some computer games can induce forgetting. Playing Tetris after watching an upsetting film has been found to reduce flashbacks of that film, possibly because thinking about a visual task stopped the brain from processing the visual images of death and injury from the ilm. However, doing a non-visual task, such as playing a general knowledge game, actually increases flashbacks.

Katherine Simon at the University of Arizona and her colleagues found the they could train people to associate a particular sound with the instruction to forget something. Then they taught the volunteers to associate other sounds with specific words. As the volunteers slept, the team reactivated the memories of some of these words using their associated sounds, while also playing the “forget” sound. A week later, the volunteers were worse at remembering these words than words that hadn’t been targeted. Hulbert says being able to exert some control over what you remember probably helps to bolster you resilience in the fact of adversity.

There are downsides, however. Hulbert’s team found that when you try to suppress a memory, you are later less likely to remember things that happened around the time you attempted suppression. Apparently quieting you hippocampus to block a memory causes an “amnesic shadow” that more generally impairs memory function.

Hulbert says that good can come from holding on to even the most awkward of memories. “For sure, bringing one to mind can be cringe-inducing, but it’s important to reflect on the good that certain embarrassing memories can bring, as learning experience that teach us what not to do again.”

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