How do you research forgetting? Did I forget something? 😊
Forgotten does not seem to mean permanently erased. It can be retrieved later depending on stimulus etc.
"... 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 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. ...
"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. ..."
"Memories are stored in ensembles of neurons called 'engram cells' and successful recall of these memories involves the reactivation of these ensembles."
From the highlights and abstract:
"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."
Graphical abstract
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