When my late lab partner Xu Liu and I first illuminated the brain cells that stored a particular memory, I felt like I was seeing a thought come to life. We stimulated a constellation of neurons inside the hippocampus of a mouse and hypothesized that these same neurons constituted the physical basis of memory, or the engram. Little did we know that we were crossing one of the most exciting frontiers in neuroscience: the ability to modify memory itself.
The phrase “memory manipulation” sounds sinister, evoking dystopian visions of erased histories or implanted lies. But in the laboratory, the reality is gentler and much more encouraging. The same discoveries that allow us to turn memories on and off in mice teach us how to heal the brain from the inside out, including how to weaken traumatic memories, strengthen fading ones, and rebalance the emotions our memories carry.
Over the past decade, this work has revealed three main principles. First, memories are malleable when stored, recalled, and restored. Second, they are distributed throughout the brain rather than in a single region. And third, they can be artificially etched into the brain. Each principle reframes what “editing memory” actually means.
When we form a memory, brain cells fire together and strengthen their connections. This process can be enhanced or impaired by different stimulation patterns. Brain stimulation with implanted electrodes or magnetic pulses can improve navigation in virtual environments. Medications, hormones, or even a little sugar can improve the brain’s ability to stabilize new experiences. And exercise stimulates the growth of new neurons and improves the health of our hippocampus, the rest of the brain and the body. The same idea works in reverse. Overstimulate the memory circuits and the strength of a memory diminishes; block the molecules that cement these connections and it weakens further.
Memories can also be altered when recalled, temporarily destabilizing a memory and opening a window of opportunity before it is stored again. Therapists already use this “reconsolidation window” when helping people living with phobias or trauma. In our animal studies, repeated reactivation of negative memories is enough to attenuate their emotional charge. Additionally, reactivating positive memories during a time of distress can completely overwhelm the negative tone. In mice, a week of “positive memory reactivation” reversed depression-like behaviors for more than a month.
Because memories are distributed throughout the brain, they are also remarkably resilient. Damage to one region rarely removes an entire experience. Instead, the brain may redirect access through alternative pathways and call upon multiple “drafts” of the memory. This redundancy offers hope for the treatment of Alzheimer’s disease: if we can strengthen still-intact pathways to memory, we can repair pieces of identity previously thought lost. The manipulation of memory therefore does not consist of rewriting who we are, but of giving the brain new paths towards itself.
The idea raises ethical concerns, as every major medical advance once did, from pacemakers to transplants. The goal of our work is to reduce suffering and thus improve our collective well-being: helping a veteran loosen the grip of a flashback, a person in recovery to decouple a craving from its trigger, or a person with Alzheimer’s disease to preserve the names of their loved ones.
Learning to reshape memory responsibly can help us heal, and the brain already edits memories every time we revisit them. Science today is simply about learning the rules. And when I think of the flickering memories with Xu, I don’t see science fiction. I see a scientific reality and a future in which memory becomes medicine for the mind.
Steve Ramirez is the author of How to Change a Memory: A Neuroscientist’s Quest to Alter the Past
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