Summary: Recent studies suggest that forgetting might not just be a mere oversight of our brains, but a dynamic response to our changing environments. Neuroscientists propose that as environments shift, forgetting irrelevant memories can foster adaptability and better decision-making.
Experiments revealed that even after certain memories in mice seemed forgotten, they could be retrieved with the right cues. This breakthrough understanding about the nature of memory could have major implications, especially for conditions like Alzheimer’s disease.
Key Facts:
- Forgetting might be a strategic feature of the brain to adapt to ever-changing environments.
- In experiments with mice, ‘lost’ memories could be revived with the right triggers or new related experiences.
- Understanding the reversible nature of “natural forgetting” might offer insights into diseases like Alzheimer’s.
Source: TCD
Neuroscientists today report the first results from experimental tests designed to explore the idea that “forgetting” might not be a bad thing, and that it may represent a form of learning—and outline results that support their core idea.
Last year the neuroscientists behind the new theory suggested that changes in our ability to access specific memories are based on environmental feedback and predictability. And that rather than being a bug, forgetting may be a functional feature of the brain, allowing it to interact dynamically with a dynamic environment.
In a changing world like the one we and many other organisms live in, forgetting some memories would be beneficial, they reasoned, as this can lead to more flexible behavior and better decision-making. If memories were gained in circumstances that are not wholly relevant to the current environment, forgetting them could be a positive change that improves our well-being.
In Cell Reports they present the first in a series of new experimental studies where the effect of natural, “every day” forgetting was investigated with respect to how normal forgetting processes affect particular memories in the brain.
The team studied a form of forgetting called retroactive interference, where different experiences occurring closely in time can cause the forgetting of recently formed memories.
In their study, mice were asked to associate a specific object with a particular context or room, and then recognize that an object that was displaced from its original context. However, mice forget these associations when competing experiences are allowed to ‘interfere’ with the first memory.
To study the result of this form of forgetting on memory itself, the neuroscientists genetically labeled a contextual “engram” (a group of brain cells that store a specific memory) in the brains of these mice, and followed the activation and functioning of these cells after forgetting had happened.
Crucially, using a technique called optogenetics they found that stimulation of the engram cells with light retrieved the apparently lost memories in more than one behavioral situation. Furthermore, when the mice were given new experiences that related to the forgotten memories, the ‘lost’ engrams could be naturally rejuvenated.
Dr. Tomás Ryan, Associate Professor in the School of Biochemistry and Immunology and the Trinity College Institute of Neuroscience at Trinity College Dublin, is lead author of the just-published journal article.
Dr. Ryan, whose research team is based in the Trinity Biomedical Sciences Institute (TBSI), said, “Memories are stored in ensembles of neurons called ‘engram cells’ and successful recall of these memories involves the reactivation of these ensembles.”
“By logical extension, forgetting occurs when engram cells cannot be reactivated. However, it is increasingly becoming clear that the memories themselves are still there, but the specific ensembles are not activated and so the memory is not recalled. It’s as if the memories are stored in a safe but you can’t remember the code to unlock it.”
Dr. Livia Autore, Irish Research Council (IRC) Postgraduate Scholar, who spearheaded this work in the Ryan Lab in Trinity, added, “Our findings here support the idea that competition between engrams affects recall and that the forgotten memory trace can be reactivated by both natural and artificial cues as well as updated with new information.
“The continuous flow of environmental changes leads to the encoding of multiple engrams that compete for their consolidation and expression.”
“So while some may persist undisturbed, some will be subjected to interference by new incoming and prevailing information. However, the interfered memories can still be reactivated by surrounding cues leading to memory expression or by misleading or novel experiences ending up in an updated behavioral outcome.”
Because we now know that “natural forgetting” is reversible in certain circumstances, this work has significant implications for disease states—such as in people living with Alzheimer’s disease for example, where these every day forgetting processes may be mistakenly activated by brain disease.
About this memory research news
Author: Tomás Ryan
Source: TCD
Contact: Tomás Ryan – TCD
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Adaptive expression of engrams by retroactive interference” by Tomás Ryan et al. Cell Reports
Abstract
Adaptive expression of engrams by retroactive interference
Highlights
- Retroactive interference causes forgetting by the competition of two memory engrams
- Forgotten engrams can be expressed or updated by reexposure to training cues
- Artificial reactivation of engram cells rescues interference-induced forgetting
- Interference is an active process that requires the activation of the suppressed engram
Summary
Long-term memories are stored as configurations of neuronal ensembles, termed engrams.
Although investigation of engram cell properties and functionality in memory recall has been extensive, less is known about how engram cells are affected by forgetting.
We describe a form of interference-based forgetting using an object memory behavioral paradigm.
By using activity-dependent cell labeling, we show that although retroactive interference results in decreased engram cell reactivation during recall trials, optogenetic stimulation of the labeled engram cells is sufficient to induce memory retrieval.
Forgotten engrams may be reinstated via the presentation of similar or related environmental information. Furthermore, we demonstrate that engram activity is necessary for interference to occur.
Taken together, these findings indicate that retroactive interference modules engram expression in a manner that is both reversible and updatable. Inference may constitute a form of adaptive forgetting where, in everyday life, new perceptual and environmental inputs modulate the natural forgetting process.
