Scientists have come to realize that our memories are not inert packets of data and they donÂ’t remain constant. Even though every memory feels like an honest representation, that sense of authenticity is the biggest lie of all. The very act of remembering changes the memory itself. Every time we recall an event, the structure of that memory in the brain is altered in light of the present moment, warped by our current feelings and knowledge.
Every memory begins as a changed set of connections among cells in the brain. itÂ’s because a network of neurons has been altered, woven more tightly together within a vast electrical fabric. This linkage is literal: For a memory to exist, these scattered cells must become more sensitive to the activity of the others, so that if one cell fires, the rest of the circuit lights up as well.
Several dozen rats were taught to associate a loud noise with a mild but painful electric shock. It terrified them—whenever the sound played, the rats froze in fear, anticipating the shock. After reinforcing this memory for several weeks, Nader hit the rats with the noise once again, but this time he then injected their brains with a chemical that inhibited protein synthesis. Then he played the sound again. “I couldn’t believe what happened,” Nader says. “The fear memory was gone. The rats had forgotten everything.” The absence of fear persisted even after the injection wore off.
The secret was the timing: If new proteins couldnÂ’t be created during the act of remembering, then the original memory ceased to exist. The erasure was also exceedingly specific. The rats could still learn new associations, and they remained scared of other sounds associated with a shock but that hadnÂ’t been played during the protein block. They forgot only what theyÂ’d been forced to remember while under the influence of the protein inhibitor.
The disappearance of the fear memory suggested that every time we think about the past we are delicately transforming its cellular representation in the brain, changing its underlying neural circuitry. It was a stunning discovery: Memories are not formed and then pristinely maintained, as neuroscientists thought; they are formed and then rebuilt every time they’re accessed. “The brain isn’t interested in having a perfect set of memories about the past,” LeDoux says. “Instead, memory comes with a natural updating mechanism, which is how we make sure that the information taking up valuable space inside our head is still useful. That might make our memories less accurate, but it probably also makes them more relevant to the future.”
Lewis had discovered what came to be called memory reconsolidation, the brain’s practice of re-creating memories over and over again. To be more specific: I can recall vividly the party for my eighth birthday. I can almost taste the Baskin-Robbins ice cream cake and summon the thrill of tearing wrapping paper off boxes of Legos. This memory is embedded deep in my brain as a circuit of connected cells that I will likely have forever. Yet the science of reconsolidation suggests that the memory is less stable and trustworthy than it appears. Whenever I remember the party, I re-create the memory and alter its map of neural connections. Some details are reinforced—my current hunger makes me focus on the ice cream—while others get erased, like the face of a friend whose name I can no longer conjure. The memory is less like a movie, a permanent emulsion of chemicals on celluloid, and more like a play—subtly different each time it’s performed. In my brain, a network of cells is constantly being reconsolidated, rewritten, remade. That two-letter prefix changes everything.
Consider the study of flashbulb memories, extremely vivid, detailed recollections. Shortly after the September 11 attacks, a team of psychologists led by William Hirst and Elizabeth Phelps surveyed several hundred subjects about their memories of that awful day. The scientists then repeated the surveys, tracking how the stories steadily decayed. At one year out, 37 percent of the details had changed. By 2004 that number was approaching 50 percent. Some changes were innocuous—the stories got tighter and the narratives more coherent—but other adjustments involved a wholesale retrofit. Some people even altered where they were when the towers fell. Over and over, the act of repeating the narrative seemed to corrupt its content. “What’s most troubling, of course, is that these people have no idea their memories have changed this much,” she says. “The strength of the emotion makes them convinced it’s all true, even when it’s clearly not.”
Reconsolidation provides a mechanistic explanation for these errors. ItÂ’s why eyewitness testimony shouldnÂ’t be trusted (even though itÂ’s central to our justice system), why every memoir should be classified as fiction, and why itÂ’s so disturbingly easy to implant false recollections. (The psychologist Elizabeth Loftus has repeatedly demonstrated that nearly a third of subjects can be tricked into claiming a made-up memory as their own. It takes only a single exposure to a new fiction for it to be reconsolidated as fact.)
The fact is we already tweak our memories—we just do it badly. Reconsolidation constantly alters our recollections, as we rehearse nostalgias and suppress pain. We repeat stories until they’re stale, rewrite history in favor of the winners, and tamp down our sorrows with whiskey. “Once people realize how memory actually works, a lot of these beliefs that memory shouldn’t be changed will seem a little ridiculous.
