One morning every spring, for exactly two minutes, Israel comes to a stop. Pedestrians stand in place, drivers pull over to the side of the road, and nobody speaks, sings, eats, or drinks as the nation pays respect to the victims of the Nazi genocide. From the Mediterranean to the Dead Sea, the only sounds one hears are sirens. “To ignore those sirens is a complete violation of the norms of our country,” Daniela Schiller told me recently. Schiller, who directs the laboratory of affective neuroscience at the Mount Sinai School of Medicine, has lived in New York for nine years, but she was brought up in Rishon LeZion, a few miles south of Tel Aviv. “My father doesn’t care about the sirens,” she says. “The day doesn’t exist for him. He moves about as if he hears nothing.”

Sigmund Schiller’s disregard for Holocaust Remembrance Day is perhaps understandable; he spent the first two years of the Second World War in the Horodenka ghetto (at the time in Poland, but now in Ukraine) and the next two hiding in bunkers scattered across the forests of Galicia. In 1942, at the age of fifteen, he was captured by the Germans and sent to a labor camp near Tluste, where he managed to survive the war. Trauma victims frequently attempt to cordon off their most painful memories. But Sigmund Schiller never seemed to speak about his time in the camp, not even to his wife.

“In sixth grade, our teacher asked us to interview someone who survived the Holocaust,” Daniela Schiller said. “So I went home after school. My father was at the kitchen table reading a newspaper, and I asked him to tell me about his memories. He said nothing. I have done this many times since. Always nothing.” A wan smile crossed her face. We were sitting in her office, not far from the laboratory she runs at Mount Sinai, on Manhattan’s Upper East Side. It was an exceptionally bright winter morning, and the sun streaming through the window made her hard to see even from a few feet away. “I long ago concluded that his silence would last forever,” she said. “I grew up wondering which of all the horrifying things we learned about at school the Germans did to him.”

Slowly, over the years, that silence closed in on her. “It wasn’t so much a conscious thing,” she said. “But I grew up with that fear in the background. What was he hiding? Why? How do people even do that?” The last question has, to a large degree, become the focus of her career: Schiller studies the intricate biology of how emotional memories are formed in the brain. Now forty-one, and an assistant professor of neuroscience and psychiatry at Mount Sinai, she specializes in the connection between memory and fear. “We need fear memories to survive,” she said. “How else would you know not to touch that burner again? But fear takes over the lives of so many people. And there is not enough that we can do about it.”

More than five per cent of Americans have experienced some form of post-traumatic stress disorder; for combat veterans, like those returning from Afghanistan and Iraq, the figure is even higher. Millions of others suffer from profound anxiety, debilitating phobias, and the cravings of addiction; those emotions appear to be formed in the same neural pathways, which means that a successful treatment for one condition might also work for others. Behavioral therapies, even those which work initially, often fail. Relapses are common, and the need for more successful treatments has never been so acute. New approaches are hard to develop, though, because most of what is known about the human brain has come from studying the neurons of other animals. One can’t simply stick a needle into somebody’s brain, grab a few neurons, drop them in a nutrient bath, and see what happens. PET scans and functional-magnetic-resonance-imaging machines have helped address the problem; they permit neuroscientists to monitor metabolic changes and blood flow in the human brain. But neither of them can measure the activity of neurons directly.

Even so, Schiller entered her field at a fortunate moment. After decades of struggle, scientists had begun to tease out the complex molecular interactions that permit us to form, store, and recall many different types of memories. In 2004, the year Schiller received her doctorate in cognitive neuroscience, from Tel Aviv University, she was awarded a Fulbright fellowship and joined the laboratory of Elizabeth Phelps, at New York University. Phelps and her colleague Joseph LeDoux are among the nation’s leading investigators of the neural systems involved in learning, emotion, and memory. By coincidence, that was also the year that the film “Eternal Sunshine of the Spotless Mind” was released; it explores what happens when two people choose to have all their memories of each other erased. In real life, it’s not possible to pluck a single recollection from our brains without destroying others, and Schiller has no desire to do that. She and a growing number of her colleagues have a more ambitious goal: to find a way to rewrite our darkest memories.

“I want to disentangle painful emotion from the memory it is associated with,” she said. “Then somebody could recall a terrible trauma, like those my father obviously endured, without the terror that makes it so disabling. You would still have the memory, but not the overwhelming fear attached to it. That would be far more exciting than anything that happens in a movie.” Before coming to New York, Schiller had heard—incorrectly, as it turned out—that the idea for “Eternal Sunshine” originated in LeDoux’s lab. It seemed like science fiction and, for the most part, it was. As many neuroscientists were aware, though, the plot also contained more than a hint of truth.

Concepts of memory tend to reflect the technology of the times. Plato and Aristotle saw memories as thoughts inscribed on wax tablets that could be erased easily and used again. These days, we tend to think of memory as a camera or a video recorder, filming, storing, and recycling the vast troves of data we accumulate throughout our lives. In practice, though, every memory we retain depends upon a chain of chemical interactions that connect millions of neurons to one another. Those neurons never touch; instead, they communicate through tiny gaps, or synapses, that surround each of them. Every neuron has branching filaments, called dendrites, that receive chemical signals from other nerve cells and send the information across the synapse to the body of the next cell. The typical human brain has trillions of these connections. When we learn something, chemicals in the brain strengthen the synapses that connect neurons. Long-term memories, built from new proteins, change those synaptic networks constantly; inevitably, some grow weaker and others, as they absorb new information, grow more powerful.

Memories come in many forms. Implicit, procedural memories—how we ride a bike, tie our shoes, make an omelette—are distributed throughout the brain. Emotional memories, like fear and love, are stored in the amygdala, an almond-shaped set of neurons situated deep in the temporal lobe, behind the eyes. Conscious, visual memories—the date of a doctor’s appointment, the names of the Presidents—reside in the hippocampus, which also processes information about context. It takes effort to bring those memories to the surface of awareness. Each of us has memories that we wish we could erase, and memories that we cannot summon no matter how hard we try. At N.Y.U. and other institutions, scientists have begun to identify genes that appear to make proteins that enhance memory, and genes that clearly interfere with it. Both kinds of discovery raise the tantalizing, if preliminary, hope of a new generation of drugs, some of which could help people remember and some that might help them forget.