Professor uncovers the nature of memories

Associate Professor Michael Anderson recently published a new study of what the brain does when a person forgets

Oregon Daily Emerald/January 14, 2004
By Caron Alarab

A University researcher is receiving international attention this week for a recent experiment exploring why people forget. With a team of Stanford researchers, Associate Professor of psychology Michael Anderson found people can use certain brain regions to block memories just as they do to control physical actions.

"It's no longer possible to say that human beings can't actively forget," said Anderson, one of the nation's leading memory researchers. "Our research demystifies the idea of memory suppression."

The findings, which were published in the Jan. 9 issue of Science magazine, support Sigmund Freud's controversial century-old theory about the existence of voluntary memory suppression.

For the experiment, Anderson recruited Stanford researcher John Gabrieli and the two co-wrote the Science article "Neural Systems Underlying the Suppression of Unwanted Memories."

The report details the steps and results of the experiment, which some experts say could help psychiatrists aid people scarred by traumatic experiences.

Although the process could be applied to both pleasant and unpleasant experiences, Anderson said he doesn't want to get ahead of himself.

"We don't know yet if this can apply to emotional memories, but we also don't know that it can't apply," he said.

Word play

Twenty-four people between 19 and 31 years old volunteered for the experiment, during which they learned unrelated noun pairs, such as "ordeal-roach" and "jaw-gum." Anderson and Gabrieli randomly divided the 36 word pairs into three sets of 12. The first two groups were asked to remember the first word of each pair and then asked to either remember or forget the second word, hence repressing memory.

For the purposes of the third group, the researchers had to determine a measurement for "simple forgetting over time." By not asking the group to either remember or to forget their pairs, the researchers left the subjects to rely on their natural memories without interference.

"People forget things over time, but not on purpose, and we had to demonstrate that," Gabrieli said. "(Anderson) had shown he could create those conditions in prior experiments."

In the second part of the experiment, the first two groups worked on their word pairs while being scanned in a functional magnetic resonance imaging machine, which produces computer images of brain tissue and function. From these images, researchers determined which parts of the brain are used for different tasks.

After completing this phase, Anderson tested the students' memory for all of the word pairs and confirmed a previous finding -- the more often people avoid thinking about the second word, the harder it became to remember it.

"People's memory gets worse the more they try to avoid thinking about it," Anderson said. "If you consistently expose people to a reminder of a memory that they don't want to think about, and they try not to think about it, they actually don't remember it as well as memories where they were not presented with any reminders at all."

The fMRI images of the subjects' brain activity revealed strong neurobiological evidence for the key concept of the experiment: People can mentally suppress unwanted memories with brain mechanisms similar to those used when stopping overt physical actions.

In other words, the brain systems -- including the prefrontal cortex -- that allow one to stop an arm motion midstream can be used to halt the retrieval of an unwanted memory.

And instead of stopping activity in brain regions linked with physical action, however, these control processes reduce brain activation in the hippocampus, a structure known to be involved in storing conscious memories of the past. It was this reduction in hippocampal activity that led the subjects to forget the rejected experiences.

"The people who suppressed their memories the best had the most activation in the prefrontal cortex," Gabrieli said. "Hence, the hippocampus and the act of suppression had an opposite connection."

Freud and beyond

Anderson and Gabrieli's latest findings provide strong evidence that Freud was on to something 100 years ago when he proposed the existence of a "voluntary repression mechanism" that erases unwanted memories.

Although he has studied Freud's research and theories about the brain, Anderson said his main interest is in how people actively control their memories and what parts of the brain are involved.

Matthew Erdelyi, a researcher at Brooklyn College in New York, has an extensive background in experimental psychology and Freudian theory. Erdelyi said Freud was first a neuroscientist, one who understood that the brain's subsystems could work against each other. Anderson's findings, Erdelyi added, show how modern technology can take century-old science a step further.

"This is very much the kind of picture Freud would feel at home with," Erdelyi said.

Since Freud, the idea of memory repression has been a vague and highly controversial idea, in part because it has been difficult to imagine how such a process could occur in the brain.

Elizabeth Loftus, a distinguished professor of social ecology at the University of California-Irvine, has been a leading voice in the debate of false-memory theory, which states that people are susceptible to suggestion, or false memories. This theory conflicts with the relevance of Anderson's experiment to traumatic cases because people might be able to fabricate their memories.

"This seems like very carefully done work, but it has little to do with traumatic experiences," she said. "People are simply misinterpreting the results of this study."

Erdelyi, who has been interviewed about Anderson's findings by European media, agreed.

"I think this is groundbreaking as a first step," he said. "But I don't think it's going to be the last."

Traumatic potential

By providing a way to map and investigate cognitive and brain processes in the laboratory, Anderson has encouraged a better understanding of neural mechanisms by which people deal with traumatic memories.

For more than a decade, University psychology Professor Jennifer Freyd has studied the process of forgetting traumatic episodes. Through her studies of people's childhood experiences, Freyd said she has found her own evidence of memory suppression in those who were abused at home.

"If the abuser was a caregiver, the abused was much more likely to forget the experience," she said. "It's actually helpful at times to forget so they can stay close to the abuser."

Although Anderson's experiment did not address traumatic memories, Freyd said the connection with brain mechanisms is extremely important.

"My best guess is there are different ways people can forget, and Michael Anderson's is one way," she said.

Considering his study focused on the suppression of relatively neutral events, Anderson stressed that future research is needed to examine the suppression of emotional experiences.

"I hope this sets off a new wave of research on how people actively forget and cope with obtrusive memories," he said. "This is really just the beginning."