Can we get better at forgetting?
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Whatever its other properties, memory is a reliable troublemaker, especially when navigating its stockpile of embarrassments and moral stumbles.

Ten minutes into an important job interview and here come screenshots from a past disaster: the spilt latte, the painful attempt at humour. Two dates into a warming relationship and up come flashbacks of an earlier, abusive partner.

The bad timing is one thing. But why can’t those events be somehow submerged amid the brain’s many other dimming bad memories?

This idea that memories have to be strengthened before they can be weakened is surprising in that it’s not how we presume memory works. But it’s a very solid finding.

- Lili Sahakyan | Associate professor

Emotions play a role. Scenes, sounds and sensations leave a deeper neural trace if they stir a strong emotional response; this helps you avoid those same experiences in the future. Memory is protective, holding on to red flags so they can be waved at you later, to guide your future behaviour.

But forgetting is protective too. Most people find a way to bury, or at least reshape, the vast majority of their worst moments. Could that process be harnessed or somehow optimised?

Method of letting go

Perhaps. In the past decade or so, brain scientists have begun to piece together how memory degrades and forgetting happens. A new study, published this month in the Journal of Neuroscience, suggests that some things can be intentionally relegated to oblivion, although the method for doing so is slightly counterintuitive.

For the longest time, forgetting was seen as a passive process of decay and the enemy of learning. But as it turns out, forgetting is a dynamic ability, crucial to memory retrieval, mental stability and maintaining one’s sense of identity.

Forgetting was seen as a passive process of decay and the enemy of learning. But as it turns out, forgetting is a dynamic ability, crucial to memory retrieval and mental stability.

That’s because remembering is a dynamic process. At a biochemical level, memories are not pulled from the shelf like stored videos but pieced together — reconstructed — by the brain.

“When we recall something, the act of recalling activates a biochemical process that can solidify and reorganise the memory that is stored,” said Andre Fenton, a neuroscientist at New York University.

It's all about editing

This process can improve memory accuracy in the long term. But activating a memory also makes it temporarily fragile and vulnerable to change. This is where intentional forgetting comes in. It’s less about erasing than editing: incrementally revising, refocusing and potentially dimming the central incident of the memory.

To intentionally forget is to remember differently, on purpose. Importantly, for scientists and therapists, intentional forgetting also may be an ability that can be practised and deliberately strengthened.

In the new study, a team led by Tracy Wang, a postdoctoral psychology fellow at the University of Texas at Austin, had 24 participants sit in a brain-imaging machine while they conducted a memory test. Dr. Wang’s co-authors were Jarrod Lewis-Peacock of the University of Texas and Katerina Placek of the University of Pennsylvania.

In the experiment, each subject studied a series of some 200 images, a mix of faces and scenes, and identified the faces as male or female, and the scenes as indoor or outdoor. Each image appeared for a few seconds, then disappeared, at which point the participant was asked to either remember or forget it; after a few seconds delay, the next image appeared. The brain scanner focused on activity in the ventral temporal cortex and the sensory cortex, regions that are especially active when a person focuses mental attention on simple images such as these.

After the participants finished, they were given a short rest and then a test. They looked at a series of images — ones they’d seen earlier and ones they hadn’t — and rated how confident they were at having seen each one. They scored well: they recalled 50 to 60 per cent of the images they’d been instructed to remember, and successfully had forgotten about 40 per cent of the images they tried to erase from memory.

The payoff came with the imaging results. When a subject’s brain activity — a measure of internal mental attention — was especially high or especially low, it typically corresponded to a failed attempt to forget an image.

A concentrated effort to forget an unwanted memory did not help dim it, nor did mentally looking the other way. Rather, there seemed to be a sweet spot — neither too little mental attention, nor too much — that allowed a memory to come to mind and then fade, at least partially, of its own accord. You have to remember, just a little, to forget.

“This suggests a new route to successful forgetting,” the authors concluded. “To forget a memory, its mental representation should be enhanced to trigger memory weakening.”

“When people were successful at doing this, there was a significant drop in their recognition confidence of images,” said Dr Lewis-Peacock. “Whether a person’s intent is to weaken memories as a part of therapy, or to change them or link them to other things as a part of daily living, this finding speaks directly to that.”

Lili Sahakyan, an associate professor of psychology at the University of Illinois, who was not involved in the research, said: “This idea that memories have to be strengthened before they can be weakened is surprising in that it’s not how we presume memory works. But it’s a very solid finding, and we are following up on it.”

The insight joins an accumulating body of evidence casting doubt on a purely linear model of forgetting, which contends that less mental attention means less remembering. That model appears to hold for some kinds of memories; deliberate ignoring is central to the forgetting strategy known as suppression.

Other strategies are not strictly linear, in that they require some engagement with the memory. One is substitution: deliberately linking an unwanted memory to other thoughts, which help alter the unwanted content when it is later retrieved. For instance, a humiliating memory could be diminished by focusing less on the feeling of shame and more on the friends who provided subsequent support.

Scientists have not yet worked out which strategies are best suited to particular kinds of unwanted memories. But any clearer understanding would be a gift to therapists working with people with disabling memories of trauma, shame or neglect. Such memories don’t fade; they remain, either as vivid recollections or as subconscious or partially conscious sources of dread and despair. A therapist’s task is to guide the patient back through these memories in a way that blunts their sting, rather than reinforces them — a dicey and often painstaking process.

Dr Lewis-Peacock said that his lab is looking at using real-time neurofeedback to nudge people who are trying to dim a memory into the mental state suggested by the new study: moderate engagement with the memory, not too much nor too little.

“We hope they can use that to say ‘Think more,’ or ‘Think less,’ to get themselves into that mental sweet spot,” he said.