Memories of experiences are strengthened when we are frequently reminded of them, a key process known as memory reactivation. Although this phenomenon helps stabilize and update memories, it can also introduce errors, leading to false memories. Using brain scans, researchers now find that the way in which reactivation occurs influences whether true or false memories arise. The findinds are detailed in the Proceedings of the National Academy of Sciences.
Past research suggests that memories are not static records of past experiences. Instead, memory is dynamic and flexible, capable of getting updated with new details. One problem of this feature is that it leaves memory vulnerable to errors and distortions, even rendering people capable of remembering events that never happened. This can lead to major problems in everyday life, such as mistaken eyewitness testimony leading to wrongful convictions.
To learn more about how memory reactivation can enhance or distort memories, cognitive neuroscientist Peggy St. Jacques at Harvard University and her colleagues Christopher Olm and Daniel Schacter had 35 volunteers take four-to-five-hour-long museum tours while wearing cameras that automatically took photos. Two days afterward, the participants had their brains scanned with functional magnetic resonance imaging (fMRI) while they looked at pictures — first photos they actually took, then images from the museum that were not part of the tour. Two days later, they were asked whether these images were from their museum tours, to see if they remembered true or false memories.
“We used the museum tour so that we could better control the characteristics of the real-world memories that people recalled while in the MRI scanner,” St. Jacques says. “Luckily for us, Harvard University has some wonderful museums, the Harvard Museum of Natural History and Peabody Museum of Archaeology and Ethnology, that are located conveniently near our lab. The museum tour was ideal because it included a sufficient number of interesting activities that people could learn about prior to the MRI scan.”
Both true and false memories were associated with activity in the left posterior parahippocampal, bilateral retrosplenial, and bilateral posterior inferior parietal cortices, areas of the brain linked with memory retrieval. However, false memories were associated with equal amounts of activity in these brain regions when people looked at both the wrong and right photos; in contrast, true memories were associated with more activity in these brain regions when looking at the right photos as opposed to wrong photos.
Moreover, compared with true memories, false memories involved greater activity in the ventromedial prefrontal cortex and hippocampus. Those brain regions are linked with flexible memory processes that allow for updating of existing memories with novel information, which unfortunately might involve false details.
“Our study provides evidence consistent with the general idea that some kinds of memory errors — in this case, falsely remembering that a ‘lure photo’ was encountered during the museum tour — can result from the operation of functional or adaptive memory processes that are otherwise beneficial,” St. Jacques says. “For example, if you couldn’t update your memory with new information you may have difficulty remembering where you parked your car today versus yesterday.”
Future research can investigate what situations might support modification of memories.
“We can retrieve memories with different goals,” St. Jacques says. “For example, accuracy: when reporting a crime to a police officer; or entertainment: when relating a funny memory to a friend.” Also, “the way that we talk or think about our personal past may result in differences in how reactivation will affect memory.”