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Memories are stored in a region of the brain called the hippocampus, shown in red in this computer illustration. (Photo Researchers, Inc.)

How Our Brains Make Memories

Surprising new research about the act of remembering may help people with post-traumatic stress disorder

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(Continued from page 3)

To Nader and his colleagues, the experiment supports the idea that a memory is re-formed in the process of calling it up. “From our perspective, this looks a lot like memory reconsolidation,” says Oliver Hardt, a postdoctoral researcher in Nader’s lab.

Hardt and Nader say something similar might happen with flashbulb memories. People tend to have accurate memories for the basic facts of a momentous event—for example, that a total of four planes were hijacked in the September 11 attacks—but often misremember personal details such as where they were and what they were doing at the time. Hardt says this could be because these are two different types of memories that get reactivated in different situations. Television and other media coverage reinforce the central facts. But recalling the experience to other people may allow distortions to creep in. “When you retell it, the memory becomes plastic, and whatever is present around you in the environment can interfere with the original content of the memory,” Hardt says. In the days following September 11, for example, people likely repeatedly rehashed their own personal stories—“where were you when you heard the news?”—in conversations with friends and family, perhaps allowing details of other people’s stories to mix with their own.

Since Nader’s original experiment, dozens of studies with rats, worms, chicks, honeybees and college students have suggested that even long-standing memories can be disrupted when recalled. Nader’s goal is to tie the animal research, and the clues it yields about the bustling molecular machinery of the synapse, to the everyday human experience of remembering.

Some experts think he is getting ahead of himself, especially when he makes connections between human memory and these findings in rats and other animals. “He oversells it a little bit,” says Kandel.

Daniel Schacter, a psychologist at Harvard University who studies memory, agrees with Nader that distortions can occur when people reactivate memories. The question is whether reconsolidation—which he thinks Nader has demonstrated compellingly in rat experiments—is the reason for the distortions. “The direct evidence isn’t there yet to show that the two things are related,” Schacter says. “It’s an intriguing possibility that people will now have to follow up on.”

A real-world test of Nader’s theory of memory reconsolidation is taking place a few miles from his Montreal office, at the Douglas Mental Health University Institute. Alain Brunet, a psychologist, is running a clinical trial involving people with post-traumatic stress disorder (PTSD). The hope is that caregivers might be able to weaken the hold of traumatic memories that haunt patients during the day and invade their dreams at night.

Brunet knows how powerful traumatic memories can be. In 1989, when he was studying for a master’s degree in psychology at the University of Montreal, a man armed with a semiautomatic rifle walked into an engineering classroom on campus, separated the men from the women and shot the women. The gunman continued the massacre in other classrooms and hallways of the university’s École Polytechnique, shooting 27 people and killing 14 women before killing himself. It was Canada’s worst mass shooting.

Brunet, who was on the other side of campus that day, says, “this was a very powerful experience for me.” He says he was surprised to discover how little was known at the time about the psychological impact of such events and how to help people who’ve lived through them. He decided to study traumatic stress and how to treat it.

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