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Why do we forget? New theory says that “forgetting” is actually a form of learning


We create countless memories while living our lives, but many of these we forget. Why? Contrary to many people's beliefs, 'memories' simply do not fade with time, 'forgetting' may not be a bad thing - it is, according to scientists, that it can represent a form of learning.

The researchers behind the new theory - outlined today in leading international journal Natural Reviews Neuroscience - suggests that changes in our ability to access specific memories are based on environmental feedback and predictability. Instead of being a mistake, forgetting can be a functional feature of the brain that allows it to interact dynamically with the environment.

In a changing world like the one we and many other organisms live in, it can be beneficial to forget some memories as this can lead to more flexible behavior and better decision making. If the memories were obtained in circumstances that are not entirely relevant to the current environment, forgetting them can be a positive change that improves our well-being.

The oblivion is due to rebuilding of circuits

The new theory suggests that forgetfulness is due to circulatory remodeling that shifts engram cells from an accessible to an inaccessible state. Credit: Dr. Nora Raschle

So in reality, scientists believe that we learn to forget some memories while preserving others that are important. Forgetting, of course, comes at the expense of lost information, but a growing body of research indicates that, at least in some cases, forgetfulness is due to altered memory access rather than memory loss.

The new theory has been proposed by Dr. Tomás Ryan, Associate Professor at the School of Biochemistry and Immunology and the Trinity College Institute of Neuroscience at Trinity College Dublin, and Dr. Paul Frankland, Professor of the Department of Psychology at the University of Toronto and the Hospital for Sick Children in Toronto.

Both Dr. Ryan and Dr. Frankland is a fellowship of the Canadian global research organization CIFAR, which enabled this collaboration through its Child & Brain Development program, which pursues interdisciplinary work in this field.

Engram cell

An engram cell. Credit: Dr. Clara Ortega-de San Luis, Ryan Lab, Trinity College Dublin

Dr. Ryan, whose research team is based at the Trinity Biomedical Sciences Institute (TBSI), said:

"Memories are stored in ensembles of neurons called 'engram cells', and successful recall of these memories involves reactivation of these ensembles. The logical extension of this is that oblivion occurs when engram cells can not be reactivated. The memories themselves are still there, but if the specific ensembles can not be activated, they can not be recalled.It's as if the memories are stored in a safe, but you can not remember the code to unlock it.

"Our new theory suggests that forgetfulness is due to circulatory remodeling that shifts engram cells from an accessible to an inaccessible state. Because the rate of forgetfulness is affected by environmental conditions, we suggest that forgetfulness is actually a form of learning that alters memory availability in in accordance with the environment and how predictable it is. "

Dr. Frankland added:

"There are several ways our brains forget, but they all act to make the engram - the physical embodiment of a memory - harder to access."

Dr. Ryan and Dr. Frankland talks about the case of pathological forgetfulness in disease:

"It is important that we believe that this 'natural forgetfulness' is reversible in certain circumstances, and that in disease states - such as in people living with Alzheimer's disease, for example - these natural mechanisms of forgetfulness are hijacked, resulting in greatly reduced engram cell availability and pathological memory loss. ”

Reference: "Forgetting as a form of adaptive engram cell plasticity" by Tomás J. Ryan and Paul W. Frankland, January 13, 2022, Nature Reviews Neuroscience.
DOI: 10.1038 / s41583-021-00548-3

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