Why Do Some Memories Stick, But Others Fade Away?

A typical day in a person’s life is filled with hundreds of moments, some brimming with excitement and some as mundane as getting dressed for work. While the brain holds the potential to remember many of these events, it only immortalizes certain ones and forgets the others. How does the brain select which memories to preserve?

In a new study published in Science Advances, a group of researchers from Boston University reported that emotional, surprising, or rewarding experiences can strengthen and prolong the memory of connected mundane events.¹ For instance, one might not recall the color of passing cars or what clothes others were wearing on a regular walk through the park. But pair that with a significant event, such as stumbling upon a childhood friend after eons or witnessing an accident, and many run-of-the-mill moments leading up to or away from the main event become imprinted in the mind. These findings could lead to better treatments for memory deficits and enhanced strategies for retaining tricky concepts.

“Memory isn’t just a passive recording device: Our brains decide what matters, and emotional events can reach back in time to stabilize fragile memories,” said Robert Reinhart, a cognitive neuroscientist at Boston University and coauthor of the study, in a statement. “Developing strategies to strengthen useful memories, or weaken harmful ones, is a longstanding goal in cognitive neuroscience. Our study suggests that emotional salience could be harnessed in precise ways to achieve those goals.”

A prominent model of how weak memories are enhanced is the “tag and capture” theory: A fleeting synaptic tag on an otherwise inconsequential memory seizes stabilizing proteins released in the vicinity by the strong event, thus transforming the fragile memory into a lasting one.² However, experiments aimed at proving this theory have yielded ambiguous results, leaving scientists divided on the theory’s credibility.

To definitively determine if strong memories enhance weaker ones, Reinhart and his team recruited 648 participants and tested their selective memory recall. The researchers showed the participants an array of images connected to high and low monetary reward and analyzed how well they retained each type of memory with a surprise memory test the next day. The team observed that the individuals were more likely to remember events that occurred after high reward stimuli. The tendency to remember such proactive memories—of moments occurring after the pivotal event—was dependent on the emotional impact of the preceding event. Contrastingly, participants were more likely to recall retroactive memories if they had certain features similar to the key event, such as a matching color.

“For the first time, we show clear evidence that the brain rescues weak memories in a graded fashion, guided by their high-level similarity to emotional events,” said Chenyang (Leo) Lin, a graduate student in Reinhart’s lab and coauthor of the study. “It’s not just timing that matters, but also conceptual overlap.”

These findings offer insights into how the brain retains everyday experiences. Reinhart thinks that they could lead to clinical interventions and applications in the education sector.

“The discovery has broad implications for both theory and practice,” he said. “In education, pairing emotionally engaging material with fragile concepts could improve retention. In a clinical setting, we could potentially rescue memories that are weak, way back in the recesses of our mind because of normal aging, for example. You can flip it, too, for people with trauma-related disorders—maybe you don’t want to rescue a distressing memory.”