A new study suggests the process of memory rewrites what is stored to bring it in line with new experiences. Writing in The Journal of Neuroscience, researchers describe how they pinpointed the hippocampus as the place where this editing occurs.
Lead author Dr. Donna Jo Bridge, of Chicago's Northwestern University Feinberg School of Medicine, where she is a a postdoctoral fellow in Medical Social Sciences, says even people's recollections of love at first sight could just be tricks of memory:
"When you think back to when you met your current partner, you may recall this feeling of love and euphoria," she says. "But you may be projecting your current feelings back to the original encounter with this person."
Memory is a continual editing process
Dr. Bridge says memories are continually adapting to constantly changing environments to help us survive and deal with what is important right now.
She explains that memory reframes and edits events to create a story to fit the present world. "It's built to be current," she adds.
The authors believe this is the first study to show how memory inserts things from the present into recollections of the past when they are retrieved. In their study, they demonstrate the exact point when that new information is implanted.
They found that the editing happens in the hippocampus, the area of the brain responsible for memory function.
Senior author Dr. Joel Voss, assistant professor of Medical Social Sciences and of Neurology at Feinberg, says, "the information that is relevant right now can overwrite what was there to begin with," adding:
"Everyone likes to think of memory as this thing that lets us vividly remember our childhoods or what we did last week. But memory is designed to help us make good decisions in the moment and, therefore, memory has to stay up-to-date."
Participants' memories of object locations changed to reflect new information
For their study, they recruited 17 men and women and invited them to carry out a three-part experiment involving looking at and moving objects around a computer screen.
The participants undertook the tests while in an MRI scanner so the researchers could monitor their brain activity.
In the first part of the experiment, the participants were invited to study various objects presented to them on a computer screen. Each object appeared on a different background, such as an ocean scene, or an aerial view of farmland.
In the next part of the experiment, the participants were presented with the objects again, but with a different background. The researchers asked them to put the objects in their correct locations, as presented to them in the first part of the experiment.
The participants always put the objects in the wrong place on the screen.
Then in the final stage of the experiment, the participants were presented with each object again, on its original background, but in three positions on the screen: the original one, the one they placed it in when doing the second part of the experiment, and a brand new position not used before. They were asked to select the position that the object had first appeared in when they first saw it.
But participants kept choosing the position they picked in the second part of the experiment, says Dr. Bridge, adding that:
"This shows their original memory of the location has changed to reflect the location they recalled on the new background screen. Their memory has updated the information by inserting the new information into the old memory."
While they were carrying out the experiments, the researchers also tracked participants' eye movements. They say this showed if there was any conflict in their choices, and it sometimes revealed more about the content of their memories than the position they eventually placed objects in.
Study may have implications for use of eyewitness testimony
Dr. Bridge says the findings could have implications for the reliability of eyewitness testimony in court cases:
"Our memory is built to change, not regurgitate facts, so we are not very reliable witnesses."
The authors acknowledge that their study was carried out as a controlled experiment, so all they can say is what they found is limited to those conditions. But they suggest it would be reasonable to assume memory behaves the same way in everyday life.
Grants from the National Institute of Neurological Disorders and Stroke and the National Institute on Aging, both of the National Institutes of Health, financed the study.
Medical News Today recently reported a study from another group of US researchers who found young adults recall memories in high definition.