To Pluck a Rooted Sorrow

Karim Nader sounds giddy as he recalls the day in November 2001 when he stood before hundreds of experts in the science of memory and presented a radical theory. At 34, with one research paper on the topic to his name, Nader was a newcomer to the field. He was so nervous, he considered ditching the San Diego conference and fleeing to Mexico: "I thought, Tijuana is only 20 minutes away. I can go there and surf for the rest of my life."

 

HEALTH FOR LIFE

To Pluck a Rooted Sorrow

Claudia Kalb

Can painful, unwanted memories be altered or even eradicated? That's the provocative question being raised by the emerging science of forgetting.

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Instead, the young scientist composed himself, walked through an intriguing rat experiment and presented his stunning conclusion. Long-term memories, Nader proposed, aren't fixed in a permanent form once they're filed away in the brain, as researchers had long believed. When a memory is recalled, it returns to an unstable state, like ice melting to water. As such, it can be altered and then it is stored again. The original memory? No longer there. The notion challenged decades of dogma and rattled seasoned scientists who believed that old memories could never be changed. Nader's nerves were so fried by the end, he says, "I couldn't believe I was still alive."

Memory isn't like the heart. You can't count its vessels or hold it in your hands. Our recollections are molecular enigmas, vast and elusive. The scientists who study them have the patience to examine neurons and enzymes, talk about "intrahippocampal infusions" and spend a lot of time hanging around rats. One of their colossal endeavors is figuring out how to enhance memory—and we could all benefit from that. (Car keys? Password?) But some of the most intriguing advances involve the science of forgetting—how and why we lose memories—and now researchers are raising the stakes with a mind-boggling question: can certain memories be intentionally targeted and changed, maybe even eradicated? In their quest for an answer, scientists are transforming what we know about how our brains process the images and sounds and feelings we encounter. One day, the research might lead to innovative treatments for conditions like posttraumatic stress disorder and addiction.

Some basic facts about memory are clear. Your short-term memory is like the RAM on a computer: it records the information in front of you right now. Some of what you experience seems to evaporate—like words that go missing when you turn off your computer without hitting SAVE. But other short-term memories go through a molecular process called consolidation: they're downloaded onto the hard drive. These long-term memories, filled with past loves and losses and fears, stay dormant until you call them up. Here's where the brain is truly ingenious: when events are supercritical or meaningful or scary—a first kiss, a baby's birth, a bike accident—stress hormones alert the amygdala, the brain's emotional control center, which then ramps up the memory-processing machinery, etching that particular event more deeply. "There's a punch to it," says James McGaugh, the University of California, Irvine, scientist who discovered this. These memories are coated with emotional glue. They stick.

Thinking back on the superhappy sticky stuff is fun. We can luxuriate in years past. But the unwanted terrible memories of rapes and robberies and combat can disrupt people's lives and, in some cases, lead to lifelong struggles with PTSD. Some 8 million Americans have the disorder in a given year and the military is at even greater risk. Antidepressants help relieve the symptoms, but fearful recollections often persist. Many patients receive cognitive behavioral therapy, which encourages them to confront their experiences in a safe way. A car-accident victim will talk through the details during repeated therapy sessions, then visit the place where the crash took place. The treatment doesn't get rid of the old memory; instead, patients form a new, competing memory of the event—I can stand at this corner and not get hit—that isn't nearly as toxic. The approach has helped countless patients, but it isn't wildly successful. Overall, symptoms improve by only about 50 percent, and that drops to one third over the long run, says Dr. Roger Pitman, professor of psychiatry at Harvard Medical School. When people see a "cue"—a reminder of the event—it can all come rushing back.

Nader wasn't thinking about PTSD when he launched his research. He became fascinated by the mechanics of memory in the late 1990s after watching Dr. Eric Kandel, a Nobel Prize winner in the field, give a lecture about how the brain processes information. A spark went off in Nader's head: what if memories were consolidated not just once, as researchers believed, but every time they were recalled? What if an original memory could be changed and "reconsolidated"? Joseph LeDoux, of New York University, remembers the moment his postdoc came up with a simple rat experiment to test the idea. "That's crazy, it'll never work," he told Nader.

Using a technique called fear conditioning, Nader gave rodents a foot shock at the same time that he played a sound. The rats now formed a memory: tone equals terror. The next day, Nader prompted the rats to recall the memory by turning the sound on again; as expected, the animals froze in fear. For a memory to be consolidated from short term to long term—from unstable to stable—it must undergo a chemical process called protein synthesis. Nader believed the same might hold true when memories were reconsolidated. Under the reconsolidation theory, some memories can be modified by new information, either intentionally or naturally after they're recalled; that may be why people who witness a crime will testify about what they heard in a news report, rather than what they saw, says LeDoux.