When you make memories, you open them up to change
12/10/2000
By Sandra Blaxley
Scientists may have found a biological reason why two people often have different memories of an event they witnessed years ago. It seems that every time an old memory is brought up to the conscious mind, the brain breaks it down, updates it and creates new proteins in the process of its repeated long-term storage.
The formation of the new proteins means that the memory has undergone a process of change, so that now it reflects the person's life experiences - and not the memory itself.
The finding is based on a study in which a certain type of fear memory was tested in animals, but many experts believe that it is possible to apply it to other types of memories in humans as well. According to them, the discovery may lead to the development of ways to change or erase memory in humans.
The study, which was done at the Center for Brain Research at New York University, was reported in August by the journal "Nature." This is the first satisfactory neurobiological explanation of the way in which memories are updated, said Dr. Daniel Schechter, professor of psychology at Harvard University and a memory expert.
"It is a mistake to think that once you record a memory, it is fixed forever," he added.
It has been known for at least 100 years that newly formed memories are still unstable, said Dr. Yadin Dodai, a neurobiologist at the Weizmann Institute in Rehovot. A blow to the head, an electric shock, or certain drugs may disrupt the process by which short-term memories are gradually transformed into long-term memories.
long, when new connections and protein syntheses are formed in the memory circuits. In the 60s, researchers showed that certain drugs could disrupt the retrieval of memories, he said, but that research didn't go far because the drugs damaged the entire brain.
In the current study, Dr. Karim Nader and Dr. Glen Shaif, research assistants at New York University, conducted experiments on rats in which a process called fear conditioning was carried out. The researchers played a certain sound to caged rats while at the same time giving them an electric shock to their legs. Later, when the rats were given the sound, they froze in place - the rats learned to be afraid.
The researchers know exactly how and where this fear memory is structured in the rat's amygdala, an area of the brain that processes emotions. According to Dr. Shaif, if a drug that blocks protein synthesis is injected into the rat's amygdala shortly after fear conditioning, it does not acquire a long-term memory of it. But if the drug is injected six hours or more later the memory is not
blocked; The brain has already created new proteins to consolidate and store the memory.
For about six hours the memory is what the scientists define as "loose" - open or susceptible to manipulation. After this period the memory stabilizes.
But according to Dr. Nader these experiments bored him. "I asked myself what happens to the memory while you remember it, does it loosen up again?"
Nader therefore proposed a new experiment: teaching animals to associate the sound with the electric shock. After a day or more, when the memory of fear solidifies in them, they will be played the sound again (to trigger the memory) and they will be injected with a drug that blocks protein synthesis.
"I argued that the drug would have no effect" on prior learning, Dr. Shaif said. If anything, the animal's fear memory should be stronger, because the drug can prevent it from learning that a sound does not necessarily connect to an electric shock - something that would strengthen the original fear memory. The two scientists argued among themselves about the result; The defeated was supposed to invite the winner for a drink. A few weeks later, Dr. Nader enjoyed a cosmopolitan cocktail.
"My jaw almost hit the floor when I saw the result," he says. Instead of freezing at the sound, the rats barely reacted. This means that memories become loose and open to change when they are retrieved, and new proteins must be made before they are stored again.
The two scientists emphasized that this finding is only a first step in the study of the way the brain consolidates memories and manipulates them. It is not known if older and more consolidated memories can also be changed or if this mechanism is limited to fear memories only.
An interesting question that arises as a result of the research is why evolution would choose a strategy that allows reshaping memories. It seems that memories need to be reliable in order to be able to guide behavior, but at the same time they must also be open to new information.
In the long run, it may be possible to use these findings clinically to erase traumatic memories, said Dr. Elizabeth Loftus, a psychologist and memory researcher at the University of Washington in Seattle. A patient will recall the disturbing event and receive a drug or other means that will disrupt the reconsolidation of the memory.
According to her, the research also clarifies the issue of false memories. If a memory that is brought up is open to changes, she said, then in the fabric of the memory, wrong information can be woven just as much as correct information. Once this happens a person has no way of knowing which of the memories is true and which is not.
Appeared in Haaretz newspaper, 12/10/2000
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