Forgetting may be a crucial step to remembering later

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Forgetting may be a crucial step to remembering later

• New study challenges traditional views on human memory retention

• Brief periods of forgetfulness could be a part of the brain's normal memory formation process

• Researcher finds 'transient memory lapses' may be periods of transition between different memory phases in humans

Evanston, Ill. --- A period of forgetfulness that follows learning a new task might be a frustrating moment, but new research at Northwestern University reveals that the period of forgetfulness could just be the brain's normal process to memory formation.

It's well established that memory retention in humans follows one of three patterns after the learning period ends: it remains constant, declines or initially improves, then remains constant or declines. A groundbreaking study led by School of Communication researcher Beverly Wrightsuggests there's another pattern lesser known in humans called a transient memory lapse. Results of her study challenge conventional wisdom about human memory formation.

Wright's study builds on seminal work from 1957, when American psychologist Leon Kamin first identified a U-shaped learning-retention curve in rats trained on an avoidance-learning task. The rats were able to remember the task soon after training, as well as hours or days after training, but the retention was quite poor one hour after training, documenting a transient memory lapse. Since then, similar memory lapses have been observed across numerous non-human species, both vertebrate and invertebrate. The current prevailing theory is that these lapses mark critical transitions between different phases of memory formation.

"We reasoned that if transient memory lapses reflect fundamental processes in memory formation in animals, they should also occur in humans," Wright said.

To test this idea in her study, Wright analyzed data from several previous research projects on 192 young adults who were given a learning task related to sound localization, but who happened to be tested at various time points after training. As predicted, Wright noted memory lapses in the test subjects that occurred between one and three hours after training, similar to the memory lapses identified in Kamin's studies.

"While experiencing a transient memory lapse, it can seem that you have forgotten the learned task, but you really haven't. It's just temporarily locked in your mind," Wright said.

The role transient memory lapses could play in memory formation

In her study, published in the journal "npj | Science of Learning," Wright says transient memory lapses in humans could reflect periods of transition between different memory phases that have been identified in animals. These phases are referred to as: short-term memory, lasting for tens of minutes; intermediate-term memory, lasting tens of minutes to hours; and long-term memory, lasting hours or days and longer.

"The idea is that transient memory lapses occur when there are time gaps between the end of one memory phase and the beginning of another," she said. "One particularly exciting aspect of these results is that the molecular underpinnings for the three memory phases have been identified in animals. That means that transient lapses in humans could provide insight into the molecular underpinnings of human memory formation."

In addition, transient memory lapses could assist the nervous system as long-term memories are formed in the brain, Wright said. For example, the lapses could serve as choice points between two opposing demands: maintaining the status quo and changing in response to experience - a neural version of tapping the brakes. She also says it's possible that transient memory lapses do not serve a direct functional role in memory formation, but instead are a marker of a key memory-formation process.

Implications for Memory Research and Applications

Wright's study challenges current descriptions of human memory retention patterns, highlighting the importance of considering transient lapses when assessing memory in clinical and research settings. It also opens new avenues for investigating memory formation in humans through behavioral observation of these lapses.

"We hope these findings will spark new investigations into the phases of human memory formation," said Wright. "The applied aspects are equally exciting, as the recognition of these lapses could affect the interpretation of human memory assessments in both the lab and the clinic."

Ruijing Ning, a former PhD student in Wright's lab at Northwestern, is a co-author on this study. Ning is currently a post-doc in the Department of Behavioral Sciences and Learning, Linköping University, Linköping, Sweden.