For some, forgetting can be a major issue, especially for those who have experienced a traumatic event they cannot forget, while for others, it seems like a blessing as they can easily forget things very quickly, according to an article published by "Neuroscience News." The dilemmas of forgetting and how it occurs have led neuroscientists to question how forgetting actually works in the brain and whether it can be sped up or slowed down. While there are still ways to understand the process well enough to provide answers, a group of researchers at Harvard University seems to have taken a small step toward understanding the impact of forgetting on the human brain.
#### Results Contradict Previous Theories
In a new study, Harvard researchers using "C. elegans," a model organism for brain research, found that forgetting does not erase or reverse changes in the brain caused by learning, as some previous scientific theories had suggested. Instead, forgetting generates a new brain state that differs from the one that existed before learning or that exists when recalling acquired behavior. In other words, what is forgotten does not completely disappear and can be reactivated with some form of a quick start. Yun Chang, a professor of organic and evolutionary biology and a member of the Harvard Brain Science Center, stated, “After forgetting, what was learned can often be reminded, and the brain is not in a state of naivety.” To simplify this idea, Chang explained: “If we had a party and then months later, we forgot everything about it, saying, ‘Oh, when was that party? Who went to the party?’ And then maybe a friend says, ‘Remember this and that? We sang you that song,’ and suddenly, the person remembers a lot of details, right?”
#### Speeding Up or Slowing Down Forgetting
The research, published in the journal "Science Advances," sheds light on how forgetting occurs in the brain at both the systems level and the molecules that the researchers discovered can speed it up or slow it down. The foundation of this work could one day be used to understand mental health issues where forgetting goes wrong, either occurring too slowly or too quickly. The new findings, for example, could lead to keys for addressing disorders such as post-traumatic stress, where unwanted memories persist strongly. Chang said, “The mechanisms provided by this study will give entry points to think about what may have happened with those neurological diseases. It helps to formulate hypotheses about the involved molecules and engaged processes, along with neuronal activity that is considered important for forgetting, and suggests ways to understand related neurological conditions.”
#### Memories Are Not Erased
Forgetting is part of the brain's natural functions due to its limited capacity. Much research has been conducted on how memories form, but little has addressed the nature of forgetting or how it occurs in the brain. Some studies suggest that when a memory is forgotten, it is simply erased, and learning is lost. Alternatively, the possibility exists that access to memory and learning becomes more challenging during the process of forgetting, but they remain in some form, which is the possibility and hypothesis that Chang's team, along with postdoctoral researchers Tihong Wu and Li Liu, tends to adopt.
#### Reactivating What Was Learned
The researchers taught the worms to recognize a scent and avoid a strain of infectious bacteria that makes them sick. However, after an hour, the worms forgot. The researchers then analyzed the brain activity of these worms and the genes expressed in their nervous systems. By comparing them to worms that had never learned the behavior or had only just completed training, they found that the neural activity and gene expression of the worms that forgot the behavior did not return to the naive state they were in before and did not match the neural activity of the worms that had just been trained, with differences noted between each group.
#### Reactivation
The researchers studied whether it was possible to remind the worms that had forgotten the training, and indeed, the worms could be reminded in just about three minutes, while training normally took around three to four hours. Chang noted, “There are still traces of memory in the [worms'] brains that can be awakened and reactivated.”
#### A Starting Point
Chang and her colleagues Wu and Liu plan to use the study's results as a starting point to continue exploring the mechanisms of forgetting and how they could ultimately be applied to mental health issues. Chang stated, “This is just the beginning of understanding forgetting, which is a crucial brain process for daily activities.”
