November 4, 2004

Pinpointing formation of false memories

By Pat Vaughan Tremmel

False memories are the controversial subject of hotly contested arguments about the validity of repressed memories that can surface years after a traumatic event and about the credibility of eyewitness accounts in criminal trials.

Because memories are imperfect under ordinary circumstances — forming, storing and retrieving them, with great variations in factors influencing those processes — it is unlikely that a one-answer-fits-all will settle those controversies soon.

But a group of researchers from various disciplines at Northwestern University literally have peered into the brain to offer new evidence on the existence of false memories and how they are formed.

Published in the journal Psychological Science, the new study used MRI technology to pinpoint how people form a memory for something that didn’t actually happen.

“Our challenge was to bring people into the laboratory and set up a circumstance in which they would remember something that did not happen,” said Kenneth A. Paller, professor of psychology and co-investigator of the study. (Brian Gonsalves, who was a doctoral student of Paller’s and who now is a post-doctoral fellow at Stanford University, is the first author of the paper.)

“We measured brain activity in people who looked at pictures of objects or imagined other objects that we asked them to visualize. Later we asked them to discriminate what they actually saw from what they imagined,” Paller said.

Extending upon considerable Northwestern research on what happens in the brain when people remember versus forget, the researchers were interested in what happens differently in the brain when false memories are produced.

“We learned that the particular parts of the brain critical for generating visual images are highly activated when people imagine images such as those we presented to our study participants,” said Paller

Many of the visual images that the subjects were asked to imagine were later misremembered as actually having been seen.

“We think parts of the brain used to actually perceive an object and to imagine an object overlap,” said Paller. “Thus, a vividly imagined event can leave a memory trace in the brain that’s very similar to that of an experienced event. When memories are stored for perceived or imagined objects, some of the same brain areas are involved.”

Take a real life example in which a police interrogator asks if you saw a particular person at a crime scene. That induces putting that person in your imagination and possibly corrupts later questioning.

“Just the fact of looking back into your memory and thinking about whether an event happened is tantamount to imagining that event happening,” Paller said. “If I ask you if something happened, you imagine it happening. Later on — a day or a year later — if I ask about that event, you have the tough judgment of deciding what happened and what was imagined.”

It is important to know that memory is fallible, Paller said. “We know that we forget quite a bit, but we’re not always in touch with the idea that our memories can sometimes can be misleading.”