When you think back on your first crush, do you remember everything about that person perfectly? At the time, you probably knew the hair color down to the exact tint and the skin tone, the sound of the voice, and precisely what was said the first time you met. Now your brain recalls it all perfectly, right? Wrong. Recent findings published in the Journal of Neuroscience reveal that what you’re experiencing today affects—and alters—what you remember about yesterday.

“New circumstances change old memories and then the brain relies on the new memory going forward, even if that memory is erroneous.” At Northwestern University, a research team led by a cognitive neuroscientist wanted to explore how memory is either consolidated or altered. The team devised a complex experiment in which participants were asked to remember the placement of images on a computer screen as the background changed and the images were relocated either by the program or manually by participants. What scientists discovered was pretty startling in terms of how the mind retrieves and uses memory:

New circumstances change old memories and then the brain relies on the new memory going forward, even if that memory is erroneous. In the experiment, when the background changed, subjects could accurately remember the image—but couldn’t accurately recall its original location on the screen. Furthermore, in subsequent phases of the experiment, the first inaccurate location recall led to future inaccurate memory retrievals…until subjects had a new experience that helped them retrieve the original memory of the object’s location.

To explain the findings, Joel Voss, an assistant professor of neuroscience at Northwestern and co-author of the study, said that in the experiment the “memory [of the object’s]…original location [had] been overwritten.” During every part of the experiment, scientists measured brain activity by MRI scans. This enabled them to see that the hippocampus (the part of the brain that directs the consolidation of individual memories) was highly active in both maintaining the “correct” recollection over time and confirming the accuracy of the newer “incorrect” memory going forward. Recall inaccuracies occurred only when subjects were asked to move the objects, indicating that the brain changes memories due to subsequent experiences. Voss’s findings indicate that during memorization, the hippocampus willingly associates two new things. Hence alterations in memory occur.

The implications of the new findings (and our continued understanding of how memory operates) reach beyond simple recollection processes and into the memory deficits associated with conditions such as Alzheimer’s and post-traumatic stress disorder (PSTD). The results suggest that problems can occur in people with Alzheimer’s due to memories “freezing”—an inability to update to the present moment. In PTSD, which is known to disrupt the memory process (and particularly the functionality of the hippocampus), problems arise because memories become stuck and don’t fully consolidate.

“Looking at an old memory from a more current perspective can reveal new, unremembered bits of information while at the same time infusing updated present-day feelings, perspectives, and beliefs.” While the research highlights the point at which memories become unreliable, there are compelling reasons why your brain constantly updates the past with information from the present. At its base this can be seen as a solid, evolution-oriented survival strategy. Updating memories with recent information makes them more relevant to the situation in which you find yourself today. This can help you do many things, from adapting to a changing environment to maintaining personal safety to predicting or recognizing threat or danger. Voss’s co-author, Donna J. Bridge, suggests that “it seems like a basic function of memory is that it is built to change [and] adapt to what is currently important to us….As you encounter new situations, new environments, it’s good to use your past to inform the future and present; sometimes that means updating your past.”

Perhaps the most relevant aspect of the research is that it underscores the fluidity of memory for all of us and how possible it is to change how you feel by allowing the present to inform the past. Voss explains, “Every time you retrieve [a memory], you have the ability to modify it.” So you are hard-wired with an easy and effective way to heal yourself of bad feelings: Looking at an old memory from a more current perspective can reveal new, unremembered bits of information while at the same time infusing updated present-day feelings, perspectives, and beliefs. So remembering that old crush who rejected you might hurt much less when you look back on it from the updated perspective of who and where you are today. That unnatural hair color? That terrible pickup line? When you recall it now, doesn’t it just seem, oh, so high school?

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