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September 20, 2012

Memory Of Events Changes With Retelling

Connie K. Ho for — Your Universe Online

Researchers from the Feinberg School of Medicine at Northwestern University recently discovered that a memory of an event can change with each retelling.

The team of scientists found that the modification of the memory of an event is due to an adjustment in brain networks that changes the placement of the memory. As a result, when an individual remembers a particular situation, it may not be exactly the same as remembered before. The study by Northwestern is the first to examine this interaction in the brain. The findings were recently published in the Journal of Neuroscience.

“A memory is not simply an image produced by time traveling back to the original event -- it can be an image that is somewhat distorted because of the prior times you remembered it,” explained lead author Donna Bridge, a postdoctoral fellow at Northwestern University Feinberg School of Medicine, in a prepared statement. “Your memory of an event can grow less precise even to the point of being totally false with each retrieval.”

The results of the study may pinpoint some of the issues that witnesses may have when giving a testimony for a trial.

“Maybe a witness remembers something fairly accurately the first time because his memories aren´t that distorted,” noted Bridge in the statement. “After that it keeps going downhill.”

It also shows that human memories have a way of adapting through time.

“When someone tells me they are sure they remember exactly the way something happened, I just laugh,” commented Bridge in the statement.

In the study, a group of participants were given the task of recalling the placement of objects on a grid over a three-day period of three separate sessions. In the first session, participants studied the placement of 180 object-location associations on a computer screen. In the next session, they took a recall test where they had to place the objects in the original location. The last session was a final recall exam. Researchers discovered that the recall of the individuals was never exactly perfect and, during the second recall test, they placed the objects closer to the incorrect location than the first recall test.

“Memories aren´t static,” remarked Bridge in the statement. “If you remember something in the context of a new environment and time, or if you are even in a different mood, your memories might integrate the new information.”

The researchers also looked at the neural signals in the brain to better understand the electrical activity in the brain. In particular, the scientists wanted to know if the neural signals in the second test correlated to the results of the first recall test. They found that there was a stronger neural signal during the first recall test as opposed to during the second recall test.

“The strong signal seems to indicate that a new memory was being laid down,” mentioned Bridge in the statement. “And the new memory caused a bias to make the same mistake again.”

The study was funded by the National Science Foundation, National Institute of Neurological Disorders, and the National Institutes of Health.

“This study shows how memories normally change over time, sometimes becoming distorted,” proposed Ken Paller, a professor of Brain, Behavior, and Cognition at Northwestern, in the statement. “When you think back to an event that happened to you long ago -- say your first day at school -- you actually may be recalling information you retrieved about that event at some later time, not the original event.”