Humans’ brains are constantly modifying their memories of the past, making the memories less accurate but better for decision-making in the future, according to new Northwestern Medicine study. 

Donna Jo Bridge, lead author of the study and a postdoctoral fellow in medical social sciences at the Feinberg School of Medicine, asked 17 men and women to recall the locations of 168 objects on a computer screen with varying backgrounds. Participants completed the experiment in an MRI scanner so their brain activity could be observed.

Scientists tracked the hippocampal region of the brain, which is involved with memory and creating an association between two arbitrary elements with which a person is not previously familiar, Bridge said.

“The hippocampus is responsible for binding or tying those two things together so you have the basis of a memory,” Bridge said. “So we showed that the same structure, the hippocampus, is also involved in modifying existing associations that we have.”

Bridge said these results indicate updating our representations of events is an adaptive mechanism that our brains must continue to do as a basic learning process.

“Memory is not just bringing up the past, it’s using the past to inform current decisions and build on current information,” Bridge said.

Bridge offered the example of a breakup with a significant other to illustrate this theory. People who are newly single might be heartbroken at first because the breakup is viewed as a loss. Later, they may project their present feelings onto the memory of the relationship and realize that the break-up was actually a good thing. An additional, simpler example, Bridge said, is recalling childhood memories of parents. They would have looked younger then, but people tend to see their parents the way they look now because their brain’s present-day view is what remains coded in memory.

Continuing with similar research, Bridge is currently working with drug-resistant epileptic patients who have had part of their brain removed. She said if the patients had the left side of their hippocampus removed instead of the right, they may lose the ability to modify memories because brain activity recorded during the study on adjusting memories always occurred on the left side. She said this could leave recollections unchanged.

“We think that changing (memories), even if it may seem like an impairment, we think, is actually adaptive and a good thing,” Bridge said.

While completing her doctoral dissertation, Bridge worked on other memory studies with Dr. Ken Paller, a psychology professor and director of the Cognitive Neuroscience Program. The study’s senior author, Prof. Joel Voss, was also a doctoral student in Paller’s lab.

Paller explained these types of studies involve re-activating memories by causing participants to retrieve the information again. Looking at the objects in Bridge’s study was a method of re-activating a memory of it and retrieving the details about where it was. Other recent research is doing the same thing, but triggering the re-activation while patients are sleeping.

“You re-activate a memory any time that you rehearse or retrieve it,” Paller said. “We think that happens also in sleep because the memories can be re-activated even though you don’t intentionally retrieve them.”

Bridge’s study was published in the Journal of Neuroscience on Feb. 5. School of Communication freshman Nicholas Hug, founder of NU’s Neuro Club, said that studies like this are what fuel his interest in the brain. 

“No matter how much we think we know about the brain, it’s still a continually evolving field,” Hug said. “For me, that’s what makes it the most fascinating field of study.”

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