Carlos Solis
We don’t have an instant “erase and move on” switch for painful memories — yet. But scientists already know how to tinker with memories: they can dull the emotion attached to a memory and, in animals, even turn memories off completely.
What a memory trace is and how researchers change it
The brain stores memory as physical changes called memory traces: patterns of activity in specific groups of neurons or changes in the connections between them. Those traces can strengthen or fade over time (for example, during sleep), and they can shift each time we recall an event.
When a memory is reconsolidated — a process called reconsolidation — people open a short window of a few hours during which the memory can be modified. Scientists have exploited that vulnerability in animal experiments and, to a degree, in clinical studies with people.
From erased neurons to memories you can switch on
Steve Ramirez, now a professor of neuroscience at Boston University, knows firsthand how destructive memories of loss can be. In 2015, while he was a PhD student studying how to manipulate memories in mice, his close friend and lab colleague Xu Liu died suddenly at 37. Ramirez struggled with grief that interfered with his daily life and work. He tried to numb the pain with alcohol and developed a serious dependence.
The turning point came in February 2021, when Ramirez realized he was drinking in the morning and counting how much he could drink in a day. Friends arranged for rehab and staged an intervention. Ramirez joined group therapy and has been sober since. He says the memory of Liu stopped being a source of helplessness and became a motivating force for his research.
In 2009 a Canadian team published a headline-making result: they located the neurons that fired when mice associated a sound with a mild electric shock and felt fear. The researchers chemically destroyed those neurons, and the animals stopped freezing when they heard the same sound — as if the fear memory had been erased.
Ramirez calls that work transformational: it showed that memories include certain highly active cells that scientists can identify and selectively target. The authors cautioned, though, that judging whether a memory truly vanished based only on behavior is tricky — absence of evidence is not evidence of absence.
Another method uses optogenetics. In 2012 Ramirez, Xu Liu and colleagues identified hippocampal neurons that responded to shock and later activated those same cells with light delivered through an optical fiber in a different context. The mice froze in fear even though there was no shock or conditioned cue — it looked like the researchers had switched the memory on by stimulating neurons. Later experiments implanted false memories in mice and showed that scientists can change a memory’s emotional tone — for example, making a negative memory less negative by activating a positive memory at the same time.
In 2022 Ramirez and his team demonstrated that if researchers activate a positive memory during reconsolidation, they can permanently blunt a negative one — and the effect lasted for months.
Does this work in people?
So far, most interventions in people are noninvasive and far less extreme than the methods used in animals. Professor Emily Holmes at Uppsala University considers the mouse work valuable because it explains basic memory mechanics, such as the timing window for reconsolidation.
A few approaches already see use or testing in humans:
- Cognitive behavioral therapy (CBT) — helps people reframe negative memories so they feel less threatening. That approach mirrors mouse experiments where activating a positive memory reduced a negative one.
- EMDR (eye movement desensitization and reprocessing) — asks people to recall a memory while performing an external task (sounds, tapping, or tracking a moving object) that disrupts normal reconsolidation and makes the memory less distressing.
- Pharmacological approaches — some drugs can interfere with forming new memories (benzodiazepines, propofol) or might weaken memories during reconsolidation (propranolol, metyrapone). Results so far are mixed.
The ‘Tetris’ trick and fewer flashbacks
Holmes proposed an unexpectedly simple tactic to reduce intrusive visual flashbacks. She noticed that flashbacks tend to be visual, and playing Tetris activates the same visual brain regions. So if someone plays a focused game of Tetris for 20 minutes right after a flashback, they can hijack visual processing and reduce how often those intrusive images recur.
In a randomized trial of ICU nurses during the COVID pandemic, that brief intervention cut flashbacks from about 14 per week to one per week after a month. Holmes and Ramirez see promise in these noninvasive strategies.
What happens if we erase memories
Even if scientists develop a safe way to erase memories in people, that capability raises many thorny questions. Holmes warns about legal risks: if someone loses memory of a crime, how can they testify in court? How would society preserve records of events? Seeking justice often plays a central role in recovering from trauma.
There are psychological risks too. People who lost memory because of drug-induced blackout — for example, after Rohypnol use — don’t always recover more easily. Even without explicit recall, the body and mind can remain traumatized, and an incomplete memory can complicate healing.
Painful memories also teach lessons and shape identity. Imagine removing a memory of a failed relationship or a workplace mistake: how would someone learn to make better choices without that experience? Many artistic, cultural, and charitable responses have sprung from suffering. Temporarily dulling a memory can help in some cases, but permanently erasing it might remove opportunities for growth.
Surveys show up to 80% of people would not want any of their memories erased forever. That makes sense: memories help define who we are. For others, whose traumatic memories destroy daily life, memory manipulation could be life-changing. Ramirez himself says he would not want his memories of his friend Xu erased.
“I always knew I did not want those memories to disappear. Solutions shouldn’t be instant — sometimes answers come decades later. I’d like to believe life is long enough for turning points that give the past deeper meaning,” Ramirez said.
Science already shows memory is not a fixed thing: researchers can weaken it, change its emotional tone, or, in animals, switch it off completely. But the right path for people will likely be complicated. The most realistic and balanced options today focus on reducing suffering safely — therapies, behavioral techniques (like the Tetris trick) and cautious drug interventions. Ethical and legal dilemmas remain, so the question of whether we should erase memories must involve society, not just science.
Based on material from BBC Science Focus
Photo: pixabay.com
