# data[].attributes.body
The amount of forgetting increases with the number of attempts to exclude the unwanted memory. He says: "Amazingly, this type of forgetting is more likely to occur when people are continuously confronted with reminders of the memory they are trying to avoid. This is contrary to intuition, which says that seeing reminders a lot ought to make your memory better. When reminders are inescapable, people must learn to adapt their internal thought patterns whenever they confront the reminder if they are to have any hope of avoiding the unwanted memory."

# data[].attributes.attachment_link.readable_text
MORE than a century after Freud suggested the existence of a repression mechanism that pushes unwanted memories into the unconscious, scientists now have hard evidence to explain how that mechanism works.

Whether we can choose to lose memories has been a controversial question since Freud claimed that it was possible, for example after traumatic events such as child abuse. Drs Michael Anderson and Collin Green, of Oregon University, have mimicked memory repression in the laboratory. They report today that people who try to forget certain words do have trouble recalling them later - even when offered money for the right answer.

This is the clearest demonstration of a direct connection between people's efforts to control awareness of a specific unwanted memory and their later ability to recall it. Dr Anderson says in today's Nature: "I do not believe that my subjects have 'erased' their memories. I believe that they have suppressed them. That is, I believe that the memories are still there, but they are difficult to access."

He believes the work could help develop new ways to unlock suppressed memories and start understanding how selective amnesia occurs. This type of amnesia may be related to that suffered by victims of child abuse or in post-traumatic stress disorder. Dr Anderson says: "Our findings are consistent with Freud's notions of suppression and repression, but go a long way towards demystifying the process. Our work allows Freud's idea to be understood in terms of widely accepted mechanisms of cognitive control."

The amount of forgetting increases with the number of attempts to exclude the unwanted memory. He says: "Amazingly, this type of forgetting is more likely to occur when people are continuously confronted with reminders of the memory they are trying to avoid. This is contrary to intuition, which says that seeing reminders a lot ought to make your memory better. When reminders are inescapable, people must learn to adapt their internal thought patterns whenever they confront the reminder if they are to have any hope of avoiding the unwanted memory."

This conforms with the discovery that people who were sexually abused by a person of trust, such as a parent, are more likely to report having forgotten the abuse than those abused by a stranger. A child growing up in a household in which they must continuously confront the person who committed the abuse is more likely to suppress the memory.

There are many everyday examples, such as the old telephone number. "You probably don't remember this any longer even though you may have dialled it thousands of times. This is because when you changed numbers, you had to learn to not accidentally dial the old one." Dr Anderson acknowledges that there is a gap between the findings and real-life clinical cases of traumatic amnesia because he used simple pairs of words that are not emotionally significant to test subjects.

However, the research provides a promising start and also provides a useful test that can reveal the way an individual controls their attention to highlight the effects of age or disease, from schizophrenia to attention defecit disorder. Another application might be in helping people who are undergoing withdrawal from drugs to control intrusive thoughts or cravings.

# data[].attributes.attachment_link.title
Scientists unlock the secrets of selective amnesia

# data[].attributes.attachment_link.description
MORE than a century after Freud suggested the existence of a repression mechanism that pushes unwanted memories into the unconscious, scientists now have hard evidence to explain how that mechanism works. Whether we can choose to lose memories has been a controversial question since Freud claimed that it was possible, for example after traumatic events such as child abuse.

# data[].attributes.attachment_link.readable_text
The human brain is estimated to include some 86 billion neurons (or nerve cells) and as many as 150 trillion synaptic connections, making it a powerful machine for processing and storing memories. We need to retrieve these memories to help us carry out our daily tasks, whether remembering where we left the car in the supermarket car park or recalling the name of someone we meet in the street. But the sheer scale of the experiences people could store in memory over our lives creates the risk of being overwhelmed with information. When we come out of the supermarket and think about where we left the car, for example, we only need to recall where we parked the car today, rather than being distracted by recalling every single time we came to do our shopping.

Previous work by Professor Michael Anderson at the Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, showed that humans possess the ability to actively forget distracting memories, and that retrieval plays a crucial role in this process. His group has shown how intentional recall of a past memory is more than simply reawakening it; it actually leads us to forget other competing experiences that interfere with retrieval of the memory we seek.

"Quite simply, the very act of remembering is a major reason why we forget, shaping our memory according to how it is used," says Professor Anderson.

"People are used to thinking of forgetting as something passive. Our research reveals that people are more engaged than they realise in actively shaping what they remember of their lives. The idea that the very act of remembering can cause forgetting is surprising and could tell us more about people's capacity for selective amnesia."

While this process improves the efficiency of memory, it can sometimes lead to problems. If the police interview a witness to a crime, for example, their repeated questioning about selected details might lead the witness to forget information that could later prove important.

Although the ability to actively forget has been seen in humans, it is unclear whether it occurs in other species. Could this ability be unique to our species, or at least to more intelligent mammals such as monkeys and great apes?

In a study published today in the journal Nature Communications, Professor Anderson together with Pedro Bekinschtein and Noelia Weisstaub of Universidad Favaloro in Argentina, has shown that the ability to actively forget is not a peculiarly human characteristic: rats, too, share our capacity for selective forgetting and use a very similar brain mechanism, suggesting this is an ability shared among mammals.

To demonstrate this, the researchers devised an ingeniously simple task based on rats' innate sense of curiosity: when put into an environment, rats actively explore to learn more about it. When exploring an environment, rats form memories of any new objects they find and investigate.

Building on this simple observation, the researchers allowed rats to explore two previously-unseen objects (A and B) in an open arena - the objects included a ball, a cup, small toys, or a soup can. Rats first got to explore object A for five minutes, and then were removed from the arena; they were then placed back in the arena 20 minutes later with object B, which they also explored for five minutes.

To see whether rats showed retrieval-induced forgetting, like humans, rats next performed "retrieval practice" on one of the two objects (e.g. A) to see how this affected their later memory for the competitor object (B). During this retrieval practice phase, the researchers repeatedly placed the rat in the arena with the object they wanted the rat to remember (e.g. A), together with another object never seen in the context of the arena. Rats instinctively prefer exploring novel objects, and so on these "retrieval practice" trials, the rats clearly preferred to explore the new objects, implying that they indeed had remembered A and saw it as "old news".

To find out how repeatedly retrieving A affected rats' later memory for B, in a final phase conducted 30 minutes later, the researchers placed the rat into the arena with B and an entirely new object. Strikingly, on this final test, the rats explored both B and the new object equally - by selectively remembering their experience with A over and over, rats had actively trained themselves to forget B.

In contrast, in control conditions in which the researchers skipped the retrieval practice phase and replaced it with an equal amount of relaxing time in the rats' home cage, or an alternative memory storage task not involving retrieval, rats showed excellent memory for B.

Professor Anderson's team then identified an area towards the front of the rat's brain that controls this active forgetting mechanism. When a region at the front of the rat's brain known as the medial prefrontal cortex was temporarily 'switched off' using the drug muscimol, the animal entirely lost its ability to selectively forget competing memories; despite undergoing the same "retrieval practice" task as before, rats now recognised B. In humans, the ability to selectively forget in this manner involves engaging an analogous region in the prefrontal cortex.

"Rats appear to have the same active forgetting ability as humans do - they forget memories selectively when those memories cause distraction," says Professor Anderson. "And, crucially, they use a similar prefrontal control mechanism as we do. This discovery suggests that this ability to actively forget less useful memories may have evolved far back on the 'Tree of Life', perhaps as far back as our common ancestor with rodents some 100 million years ago."

Professor Anderson says that now that we know that the brain mechanisms for this process are similar in rats and humans, it should be possible to study this adaptive forgetting phenomenon at a cellular - or even molecular - level. A better understanding of the biological foundations of these mechanisms may help researchers develop improved treatments to help people forget traumatic events.

The research was funded by the Medical Research Council, the National Agency of Scientific and Technological Promotion of Argentina and the International Brain Research Organization.
Reference
Bekinschtein, B, et al.A Retrieval-Specific Mechanism of Adaptive Forgetting in the Mammalian Brain. Nature Comms; 7 Nov 2019; DOI: 10.1038/s41467-018-07128-7

# data[].attributes.attachment_link.keywords[]
medical research council (mrc) medical research council (mrc) michael anderson michael anderson memory

# data[].attributes.attachment_link.keywords[]
spotlight on neuroscience spotlight on neuroscience

# data[].attributes.attachment_link.keywords[]
memory medical research council (mrc) cognition and brain sciences unit (cbsu)

# data[].attributes.attachment_link.keywords[]
school of clinical medicine school of clinical medicine

# data[].attributes.attachment_link.keywords[]
medical research council (mrc) cognition and brain sciences unit (cbsu)

# data[].attributes.attachment_link.title
Selective amnesia: how rats and humans are able to actively forget distracting memories

# data[].attributes.attachment_link.description
Our ability to selectively forget distracting memories is shared with other mammals, suggests new research from the University of Cambridge. The discovery that rats and humans share a common active forgetting ability - and in similar brain regions - suggests that the capacity to forget plays a vital role in adapting mammalian species to their environments, and that its evolution may date back at least to the time of our common ancestor.

# data[].attributes.body
To start with, amnesia puts us in confusion. There are some common circumstances in which we get confused. Sometimes during a conversation, we suddenly get stuck because we can't tell the name of the latest movie or a person we've known for years. When taking an exam, we may find ourselves unable to spell the word we studied the other day. In these cases, we have no idea why we forget such things that we don't even put effort into memorizing. We keep thinking about what possibly leads to this, attempting to recall the moment we first got informed. In other words, we are confused.

# data[].attributes.body
Have you ever seen any tv drama character suffering from headaches and confused about his or her lost memory? It usually turned out that the character experienced a traumatic event when he was little, either a kidnap or a witness of a suicide. Notwithstanding the fear he had been through, the character forgot the event right after the startle. This is a common response to fear called selective amnesia. All people experience selective amnesia in their lives. Previous work by Professor Michael Anderson at the Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, showed that humans possess the ability to actively forget distracting memories, which improves the efficiency of the memory. However, selective amnesia, as a response to fear, can result in anxiety, false memory, and social inability

# data[].attributes.body
Selective amnesia, as a response to fear, can cause confusion, depression and social inabilities.