Memories stick with us for a reason. We hang onto important events and life experiences from our past, however, many of these seemingly crucial memories have also been forgotten. The act of forgetting often has a negative connotation. Many perceive forgetting as a form of memory loss. However, scientists researching forgetfulness have proposed an alternate theory. It appears as though forgetting may not result in memory loss at all, but an alteration of access to our memories.
While remembering and recalling memories may provide many benefits, forgetting memories also has a functional role in allowing our brains to operate at an optimal level. Having flexibility in recalling memories we find useful and forgetting memories that may not be relevant help us with certain functions, such as decision making. We often remember memories that are important, and forget memories that are not. This comes at a cost, however, when important information is lost.
Drs. Tomás Ryan, Associate Professor in the School of Biochemistry and Immunology at the Trinity College Institute of Neuroscience and Dr. Paul Frankland, Professor in the Department of Psychology at the University of Toronto led a study observing how forgetting involves a circuit remodeling process that changes as a result of dynamic interaction with the environment. Canadian-based research organization, CIFAR, collaborated on this project with Dr. Ryan and Dr. Frankland through its Child & Brain Development program.
The science behind forgetting and memory recall suggests that memories are stored within engram cells. These are ensembles of cells that are reactivated when successful recall takes place. In contrast, forgetting occurs when the engram cells cannot be reactivated.
While different forms of “natural forgetting” are impacted by such variables as time course and reversibility, all forms of forgetting are tied to circuit remodeling. When engram cells are in an accessible state, they can be reactivated. Similarly, the cells may also be inactivated making them inaccessible. In this scenario, the memories still exist, but cannot be accessed.
Dr. Ryan compared this to storing memories in a safe, but without remembering a code to unlock it.
“Our new theory proposes that forgetting is due to circuit remodeling that switches engram cells from an accessible to an inaccessible state,” Ryan explains in a statement. “Because the rate of forgetting is impacted by environmental conditions, we propose that forgetting is actually a form of learning that alters memory accessibility in line with the environment and how predictable it is.”
Dr. Ryan and Dr. Frankland acknowledge in healthy individuals, natural forgetting may be reversed in most circumstances. Whereas in cases with those living with neurological diseases, such as Alzheimer’s disease, natural forgetting mechanisms are hijacked and pathological memory loss occurs with a reduction of engram cells.
“There are multiple ways in which our brains forget, but all of them act to make the engram – the physical embodiment of a memory – harder to access,” says Frankland.
The findings from this study were first published in the journal Nature Reviews Neuroscience.