Every time you remember an event from the past, your brain networks change in ways that can alter the later recall of the event. So the next time you remember it, you might recall not the original event, but what you remembered the previous time.

“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,” said Donna Bridge, a postdoctoral fellow at Northwestern University Feinberg School of Medicine and lead author of the paper on the study recently published in the Journal of Neuroscience.

The findings have implications for witnesses giving testimony in criminal trials, Bridge noted. “Maybe a witness remembers something fairly accurately the first time because his memories aren’t that distorted,” she said. “After that it keeps going downhill.”

The reason for the distortion, Bridge said, is the fact that human memories are always adapting. “Memories aren’t static,” she noted. “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.”