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Brain-Updating Machinery May Explain False Memories
http://www.nytimes.com/2000/09/19/science/19MEMO.html

September 19, 2000

By SANDRA BLAKESLEE

Scientists may have found a biological reason to explain why two
people who witness the same event will, years later, often have
different memories of what happened.

 It seems that every time an old memory is pulled into
consciousness, the brain takes it apart, updates it and then makes
new proteins in the process of putting the memory back into
long-term storage. The fact that new proteins are made means that
the memory has been transformed permanently to reflect each
person's life experiences   not the memory itself.

 The finding is based on research involving a specific kind of fear
memory in animals, but many experts predict that it may also hold
true for other kinds of memories in humans. They also say that the
discovery could lead to ways of altering or erasing people's
memories.

 The research, carried out at the Center for Neural Science at New
York University, was described in the Aug. 17 issue of the journal
Nature. This is the first good neurobiological explanation of the
way memories are updated, said Dr. Daniel Schacter, a Harvard
psychology professor and a memory expert. "It's a mistake to think
that once you record a memory, it is forever fixed," he said.

 Dr. Elizabeth Loftus, a psychologist who studies memory at the
University of Washington in Seattle, said: "This is very
interesting research. We're on the brink of being able to figure
out how you might accomplish something like memory engineering."

 It may be possible to erase traumatic memories in people who are
plagued by them, she said, and to better understand how false
memories are implanted into people's minds when they are given
suggestions that they want to believe.

 It has been known for at least 100 years that newly formed
memories are initially unstable, said Dr. Yadin Dudai, a
neurobiologist at the Weizmann Institute of Science in Rehovot,
Israel. A bump on the head, an electric shock or certain drugs can
disrupt the process that gradually turns short-term memories into
long-term memories through the production of new connections and
protein synthesis in memory circuits.

 In the 1960's, researchers showed that certain drugs could
interfere with the recall of memories, he said, but the research
did not get very far because the drugs affected the entire brain
and could not be traced to cellular mechanisms in memory networks.

 Dr. Karim Nader and Dr. Glenn Shafe, research assistant professors
at N.Y.U., carried out the new experiments on memory recall in ways
that reveal those cellular mechanisms with much greater precision.
In a process called fear conditioning, they simultaneously played a
tone and delivered an electric shock to the feet of caged rats.
Later, when the rats heard just the tone, they froze; they had
learned to be afraid.

 Researchers know exactly how and where this fear memory is
hardwired in the rat's amygdala, a part of the brain that processes
emotions.

 If the rat's amygdala is injected with a drug that blocks protein
synthesis shortly after fear conditioning, it does not acquire
long-term memory of the fear, Dr. Shafe said.

 But if the drug is injected six or more hours later, the memory is
not blocked; the brain has made new proteins to consolidate and
store the memory.

 For six hours or so the memory is what scientists term "labile"
open or sensitive to some kind of manipulation. After this period,
the memory is firmly in place.

 "I was bored with these experiments," Dr. Nader said. "I began
thinking, what happens to a memory when you remember it? It would
be so cool if it became labile again." He proposed a new
experiment: animals would be trained to associate the tone with the
electric shock. The researchers would wait a day or more for the
fear memory to consolidate. Then they would present the animal with
the tone (to retrieve the memory) and a drug that blocks protein
synthesis.

 "I said the drug would have no effect" on past learning, Dr. Shafe
said. If anything, the animal's fear memory should be stronger
because the drug could deter the animal from learning that a tone
was not necessarily associated with a shock   and that would
reinforce the original fear memory. The two scientists bet a
cocktail on the outcome. A few weeks later, Dr. Nader won a
cosmopolitan.

 "My jaw just hit the floor when I saw the result," he said.
Instead of freezing at the tone, the rats scarcely reacted. It
means memories become labile and open to revision every time they
are recalled, Dr. Nader said. And new proteins have to be made
before the memories are put back into storage.

 Both researchers emphasized that this finding was only a first
step in exploring the biology of how the brain consolidates and
manipulates memories. It is not known if much older and more
established memories are open to editing or if this mechanism is
restricted to fear memories alone.

 Why evolution would choose a strategy that permits memories to be
highly malleable is an interesting question. Memories need to be
reliable to guide behavior, but they also need to be open to new
information.

 In the long run, these findings may be used clinically to erase
traumatic memories, Dr. Loftus said. A patient would recall the
troubling event and be given a drug or other agent to disrupt the
memory from being reconsolidated.

 The research also sheds light on false memories, she said. If a
recalled memory is open to revision, incorrect as well as correct
information can be woven into the fabric of a memory. Once that
happens, a person has no way of knowing what is true or not true.
Yet people put faith in their memories to guide their decisions,
she said.
   
 

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