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Weizmann Institute scientists have discovered a new rule in the brain's memory operation

The discovery may contribute to the development of methods to treat mental traumas

Avi Blizovsky

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Is it possible to intentionally forget only certain memories, without harming other memories? Many of us would surely be happy to discover that unpleasant memories can be erased. Such an ability may have a special meaning when it comes to traumatic memories, which disrupt the life of the rememberer. It is possible that in the future we will be able to erase or at least dim certain types of memories in a controlled manner. A new rule in the functioning of the brain, recently discovered by Weizmann Institute of Science scientists led by Prof. Yadin Dodai from the Department of Neurobiology, may take us an important step forward on the way to achieving this goal.

Every memory we acquire immediately after its acquisition undergoes a process of maturation ("consolidation"), in which it becomes resistant to external stimuli and various drugs that can erase it. Until recently, it was accepted that this ripening process occurs only once in the life of the memory, and when the time window of sensitivity to these "memory erasers" closes (usually about an hour or two after the memory was acquired), the durability remains the same for the duration of the memory's existence. Recently, however, evidence has begun to be found that a memory may become susceptible to interference again for a short time after it has been retrieved (that is, immediately after it has been used). If indeed this is the face of things, then this means that if the brain remembers something, immediately after the recollection it will be possible to reactivate the "memory erasing" factors and erase the memory, even though a long time has passed, even years, since it was acquired.

The problem was that experiments on this innovative topic, in leading laboratories in the world, showed that in some cases it is possible to delete an old memory when it is retrieved, but in other cases no evidence of this was found. Prof. Duday's group has now identified a new rule in the operation of memory systems in the brain, which, apart from shedding light on the way the brain works and the stability of memories, is also able to explain the discrepancy between the various studies. The discovered rule determines under what conditions the extracted memory becomes re-sensitive to the possible activity of the "memory erasers". To understand this rule, it is worth remembering that many pieces of information found in our memory have many connections, some of which contradict each other (conflicting). For example, a certain food can be remembered in a tasty or unpleasant context, a certain person can be remembered in a pleasant or unpleasant context, and more. When we taste the same food or see the same acquaintance, in the blink of an eye all these contexts are pulled from our memory together, or some of them, but in the end, only one of them dictates the behavior more than others (ie becomes dominant). It is this memory that will determine, for example, whether we will eat the food or reject it, or whether we will smile at our acquaintance or whether we will ignore him.
Prof. Dodai's group discovered that only that memory that "won the competition", came to the surface following the retrieval and took over the behavior, was re-exposed to a window of time of sensitivity, and it must mature again before it returns and is established as a long-term memory. In other words, the "victorious" memory may under certain conditions, as a result of its victory, lose its future. In a more concise language, it can be said that the stability of a removable memory is inversely proportional to its dominance. This discovery may help in the future to develop methods for erasing unwanted memories, and as a result maybe even to treat mental traumas.

Studies dealing with the physical basis of the basic properties and mechanisms of memory, and especially those that require chemical and other interventions, are done in animals. Prof. Dudai and the members of his research group performed their experiments on rats and fish, which are particularly suitable for the purpose of the research: the rats learned to remember tastes, the fish learned to remember flashes of light, and in both cases, the animals were trained to remember conflicting memories, that is, a taste is sometimes good and sometimes bad, The light signal heralds danger or it does not herald it. In both sexes, it was possible to show that the dominant context, the one that prevailed and dictated the behavior after retrieval, was the only one that could be erased by administering appropriate drugs within a few minutes of its retrieval. The fact that as far as the "basic hardware" of the memory systems in the brain is concerned, there is a great deal of similarity between the different species of animals, including humans, opens the door to the hope that non-toxic drugs that are found to be effective in erasing memory in this way in animals will have a similar effect in humans as well. A person. So far, however, the way to carry out the process in humans has not yet been tested.

The results of the research were published last Thursday, 21/8/03 in the scientific journal "Science". In addition to Prof. Dodai, the research students Mark Eisenberg, Tali Cubillo and Diego Berman participated in the research team.

Yuval Dror's version, Haaretz

erasing memories? According to Israeli researchers - this is not science fiction

By Yuval Dror

Researchers from the Weizmann Institute believe they have found a rule that determines which memories become "sensitive to erasure" after being retrieved; succeeded in erasing memories in rats

Everyone has at least one memory they'd be happy to forget. Until recently, researchers assumed that memories cannot be erased - especially if they are "long-term". However, a new rule in the functioning of the brain, discovered by scientists from the Weizmann Institute led by Prof. Yadin Dodai from the Department of Neurobiology, may in the future make it possible to erase certain memories.

"Memory can be found in two states," explains Prof. Dudai, "active - when the brain makes use of the memory - or dormant, when it is in the brain's internal network but has not yet been retrieved. When we pull out a memory from the place where it is stored, it becomes active." According to Dudai, in the first hour or two after its acquisition, each memory goes through a process of maturation ("consolidation"), in which it becomes resistant to external stimuli and drugs that can erase it. "In this window of opportunity, the memory is unstable and it can be erased," says Dudai.
Until recently, the prevailing assumption was that the maturation process occurs only once in the life of the memory, and that when the time window of sensitivity to the "memory erasers" closes, the memory becomes durable and can no longer be erased. However, evidence has recently been found that whenever a memory is retrieved, it becomes susceptible to interference again for a short time, immediately after it is used. However, the results of the experiments were inconclusive.
Prof. Dudai believes that in a series of experiments he performed together with his students on rats and fish - the results of which were published yesterday in Science magazine - he found the rule according to which the brain determines which memory becomes "sensitive to erasure".

"Memory is largely related to associations. 'It's hot at the beach'. It's an association," says Dodai, "every memory usually has a collection of associations, but only one emerges distinctly and takes over. Let's say that I remember that in a certain restaurant it was pleasant, quiet but not tasty. All the memories are pulled together, with one being dominant. If, for example, the memory that states that the restaurant was not tasty is the dominant one - it will take over my behavior and determine it. What we found is that the dominant memory, even if it is long-standing, becomes susceptible to erasure immediately after it is retrieved."

To prove this claim, experiments were carried out on rats and fish. Teach the animals something (for example: a certain food is tasty or not tasty) and then, after the animal has retrieved the memory from the brain, use a special drug to erase it. Indeed, it turned out that what the animal remembered, disappeared as if it had not been. "The period of time for deletion is short, less than an hour," says Dudai. "The principle we uncovered is that precisely the memory that 'won the competition' exposes itself to the danger of erasure."

According to Dudai, clear rules are rarely discovered in the brain's behavior. "From the moment the rule is revealed, it is possible to develop practical directions that will help us help people who suffer from trauma." However, while drugs capable of erasing the active memory have been developed for rats and fish, human experiments are much more problematic. "You must be sure that you delete only a certain memory and not another memory, and of course make sure that there are no side effects", explains Dodai. For this reason, he is trying to develop behavioral methods to help erase the retrieved memories. "If I tell you that some toy was invented in 1900 and now I ask you to count back in threes from 627, you will find that after a minute you will have trouble remembering what I told you earlier. Such methods are harmless, and may be effective in erasing the desired memory."

The brain savant

One response

  1. How to erase the memory of a surprise party that I accidentally knew was being thrown and I want it to be a surprise? Waiting for a quick answer please! Mala and Noa

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