The science of forgetting

As the baby boom generation ages towards retirement, attention grows over how people can remain mentally sharp. Alzheimer’s and other forms of dementia make  boomers start to worry when they lose their car keys or stumble over a name. At the same time, Internet search engines
and home data storage have made the actual need to remember less important. Add to this the rapid pace of media and the public’s seemingly relentless focus on immediacy over history, and it seems like a wholesale assault on memory is sweeping the culture. So a story like “The Forgetting Pill Erases Painful Memories” recently appearing in Wired magazine would seem to support the current culture of amnesia.

But what the Wired story does instead, to its credit, is to remind us of the relative character of memory and the problem of excess when it comes to the mind. “The Forgetting Pill Erases Painful Memories” addresses ways that neuroscience is working on the problem of traumatic memory and the difficulties of moving beyond remembrances of loss, violence, and abuse. Say what you will about America’s military adventures around the world, but big changes have been taking place in the way our culture thinks about the effects of war on those we send into combat theaters. And wartime PTSD is but a single component of the larger issue of psychological trauma. Until relatively recently, much of the treatment for such conditions took place in the context of individual or group psychotherapy, or through ways of providing suffers with tools through cognitive behavioral means. But now scientists know a lot more about the actual physiology and chemistry of the mind, with a host of emerging medicines and methodologies at their disposal.

As explained by Wired’s Jonathan Lehrer, “Once you start questioning the reality of memory, things fall apart pretty quickly. So many of our assumptions about the human mind—what it is, why it breaks, and how it can be healed—are rooted in a mistaken belief about how experience is stored in the brain. (According to a recent survey, 63 percent of Americans believe that human memory “works like a video camera, accurately recording the events we see and hear so that we can review and inspect them later.”) We want the past to persist, because the past gives us permanence. It tells us who we are and where we belong. But what if your most cherished recollections are also the most ephemeral thing in your head?

“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. The scientists aren’t sure about this mechanism, and they have yet to analyze the data from the entire 10-year survey. But Phelps expects it to reveal that many details will be make-believe. “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.”

As Lehrer continues, “Reconsolidation provides a mechanistic explanation for these errors. It’s why eyewitness testimony shouldn’t be trusted (even though it’s central to our justice system), why every memoir should be classified as fiction, and why it’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.)

“And this returns us to critical incident stress debriefing. When we experience a traumatic event, it gets remembered in two separate ways. The first memory is the event itself, that cinematic scene we can replay at will. The second memory, however, consists entirely of the emotion, the negative feelings triggered by what happened. Every memory is actually kept in many different parts of the brain. Memories of negative emotions, for instance, are stored in the amygdala, an almond-shaped area in the center of the brain. (Patients who have suffered damage to the amygdala are incapable of remembering fear.) By contrast, all the relevant details that comprise the scene are kept in various sensory areas—visual elements in the visual cortex, auditory elements in the auditory cortex, and so on. That filing system means that different aspects can be influenced independently by reconsolidation.

“The larger lesson is that because our memories are formed by the act of remembering them, controlling the conditions under which they are recalled can actually change their content. The problem with CISD is that the worst time to recall a traumatic event is when people are flush with terror and grief. They’ll still have all the bodily symptoms of fear—racing pulse, clammy hands, tremors—so the intense emotional memory is reinforced. It’s the opposite of catharsis. But when people wait a few weeks before discussing an event—as Mitchell, the inventor of CISD, did himself—they give their negative feelings a chance to fade. The volume of trauma is dialed down; the body returns to baseline. As a result, the emotion is no longer reconsolidated in such a stressed state. Subjects will still remember the terrible event, but the feelings of pain associated with it will be rewritten in light of what they feel now.”