Brain Doesn't Always Spot False Memories

Human Brain Not Wired to Remember With 100% Accuracy

By Miranda Hitti
WebMD Medical News 

Feb. 2, 2005 - Memory isn't perfect, even for the sharpest minds & new insights are revealing memory's flaws.

A test of true & false memories indicates that the brain doesn't always spot misinformation. It's the sort of news that makes criminal lawyers sit up & take notice.

But memory's ebb & flow isn't just a matter for the courts. You've probably experienced it in your own life.

"i.e., you may have a memory of witnessing an important event such as your wedding day, or the birth of a child," write Johns Hopkins University researchers Yoko Okado & Craig Stark, PhD, in February's Learning & Memory.

"You feel you remember these events, but the memories are most likely distorted to some degree."

Those memory-storing glitches may not be huge. You might even swear they don't exist, but if you could time travel to check the facts, you might find some details don't match your memory.

It's normal for memories to fade a bit around the edges, especially over time. People just aren't wired for total recall with 100% accuracy.

Truth vs. Lies

Okado & Stark recently studied true & false memories. They showed 8 vignettes to 20 people aged 18 to 34.

Each vignette unfolded in a series of 50 slides. After a short break, participants watched the vignettes again. They didn't know it, but 12 slides were slightly different in the second viewing.

e.g., one vignette showed a man stealing a woman's wallet & hiding behind a tree. In another version, he hid behind a car.

While watching the vignettes, participants' brains were scanned with functional magnetic resonance imaging (fMRI). The scans showed active brain areas.

Two days later, participants were quizzed about what they recalled & the source of those memories - the original presentation, the second presentation, or both.

Misinformation was scored as a false memory if the participants recalled an item as being presented in either slide show.

Participants endorsed misinformation in 47% of the questions. In 27% of those cases, they said they'd seen the detail in the vignette's first (true) version. They attributed the other 20% to both vignette versions.

Brain to Blame?

Brain scans predicted if their memories were accurate or had false information. Two regions of the brain were active in encoding true & false memories. Previous studies have shown that these brain areas (hippocampus) are active during the formation of memories.

Other brain regions, including the prefrontal cortex, put the memories in context. Those areas were less active while participants watched the inaccurate second slide presentation. The weak activity in these regions during the inaccurate presentation indicates that the details of it were poorly encoded during the second presentation.

As a result they were more easily placed in the context of the first slide presentation, creating a false memory.

That set up a "vulnerable situation," says memory expert Elizabeth Loftus of the University of California, Irvine. The misinformation slipped easily into the context of the original event, "creating strong false memories," writes Loftus in a Learning & Memory commentary.

Forging False Memories

Vivid Imagination Can Trick the Brain, Study Shows

By Miranda Hitti
WebMD Medical News

 

Oct. 21, 2004 -- The power of suggestion can play games w/ memory, persuading people that false memories are real, according to Northwestern University experts.

While we might like to think that our memories are accurate logs of our lives, that's not always true.

Our memories are imperfect to begin with & forgetfulness isn't the only glitch. The brain can also be convinced that events that never took place actually did occur. That's what happened in Northwestern's recent experiment with 11 adults.

The test was conducted by researchers including Brian Gonsalves, formerly of Northwestern's psychology department & now a postdoctoral fellow at Stanford University.

First, participants lay in a magnetic resonance imaging (MRI) device, which measured brain activity during a task. The researchers showed them photos or asked them to generate visual images of objects that were not pictured; instead they were given detailed clues to build visual images.

Meanwhile, brain imaging scans were done to see which area of the brain was responding during the test.

Twenty minutes after getting out of the MRI machine, subjects heard a random sequence of words, including 175 objects they had seen in the photographs, 175 objects that they had been asked to imagine, and 175 objects that hadn't been displayed or mentioned.

Sometimes, participants were sure that they remembered seeing photos of objects that they had only visually imagined during the study phase of the experiment.

In other words, the brain persuaded itself that it had seen objects that were visually imagined. As far as the brain was concerned, those false memories were true.

Brain imaging scans showed that different areas of the brain were at work w/false & accurate memories.

The mental images left a trace in the brain that was later mistaken for the trace that would have been produced had the object actually been seen, say the researchers.

The brain activity on MRI during the study phase could predict which objects would subsequently be falsely remembered as having been seen in a photograph.

"We know we can forget quite a bit, but we're not always in touch w/the idea that our memories can sometimes be misleading," says Northwestern psychology professor Kenneth Paller, in a news release.

Paller worked on the study, which appears in the October issue of the journal Psychological Science.

By Willow Lawson

Researchers found that people who intentionally tried to forget certain words couldn't recall them later, even when they were offered cash for the right answer.

"People in these studies are, in essence, pushing unwanted memories in to the unconscious, causing them to be forgotten later on," says Michael Anderson, a University of Oregon psychology professor who began his research to find out why victims of childhood abuse have problems recalling the abuse.

Debate Continues Over Freud

The existence of repression has been controversial since Freud claimed people could consciously forget memories of traumatic experiences, like abuse, more than 100 years ago.

But in recent years, repression has been central to the turbulent debate over "recovered memory," whether it's possible to repress a memory of a traumatic experience like childhood sexual abuse & then remember it many years later.

Anderson's study mirrors the findings of another University of Oregon professor, Jennifer Freyd, author of Betrayal Trauma: The Logic of Forgetting Childhood Abuse.

"Adults who report child abuse perpetrated by a caregiver are much more likely to report memory impairment than are adults who report child abuse perpetrated by a non-caregiver," says Freyd. "Anderson's new research technique may eventually prove very important for accounting for forgetting in real-life social situations."

But Anderson admits that forgetting a word in a memorized word pair remains very different from repressing traumatic experiences.

"In the current experiments, we use simple pairs of words that are not emotionally significant to the subject & test their memory after a brief delay," says Anderson. "In amnesia for trauma, we are obviously dealing with much more distinctive, emotionally significant experiences."