January 09, 2004
Stanford Researchers Find Evidence Of Memory Supression Mechanism

Using functional magnetic resonance imaging (fMRI) researchers at Stanford University have found additional evidence that the brain has biological mechanisms for making specific memories harder to access.

Anderson first revealed the existence of such a suppression mechanism in the brain in a 2001 paper published in Nature titled "Suppressing Unwanted Memories by Executive Control." He took the research a step further at Stanford by using brain imaging scans to identify the neural systems involved in actively suppressing memory. The core findings showed that controlling unwanted memories was associated with increased activation of the left and right frontal cortex (the part of the brain used to repress memory), which in turn led to reduced activation of the hippocampus (the part of the brain used to remember experiences). In addition, the researchers found that the more subjects activated their frontal cortex during the experiment, the better they were at suppressing unwanted memories.

"For the first time we see some mechanism that could play a role in active forgetting," Gabrieli said. "That's where the greatest interest is in terms of practical applications regarding emotionally disturbing and traumatic experiences, and the toxic effect of repressing memory." The Freudian idea is that even though someone is able to block an unpleasant memory, Gabrieli said, "it's lurking in them somewhere, and it has consequences even though they don't know why in terms of their attitudes and relationships."

The experiment

Twenty-four people, aged 19 to 31, volunteered for the experiment. Participants were given 36 pairs of unrelated nouns, such as "ordeal-roach," "steam-train" and "jaw-gum," and asked to remember them at 5-second intervals. The subjects were tested on memorizing the word pairs until they got about three-quarters of them right -- a process that took one or two tries, Anderson said.

The participants then were tested while having their brains scanned using functional magnetic resonance imaging (fMRI) at Stanford's Lucas Center for Magnetic Resonance Spectroscopy. The researchers randomly divided the 36 word pairs into three sets of 12. In the first set, volunteers were asked to look at the first word in the pair (presented by itself) and recall and think about the second word. In the second set, volunteers were asked to look at the first word of the pair and not recall or think of the second word. The third set of 12 word pairs served as a baseline and was not used during the brain scanning part of the experiment. The subjects were given four seconds to look at the first word of each pair 16 times during a 30-minute period.

After the scanning finished, the subjects were retested on all 36 word pairs. The researchers found that the participants remembered fewer of the word pairs they had actively tried to not think of than the baseline pairs, even though they had not been exposed to the baseline group for a half-hour.

"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."

While the unlocking of repressed memories has been viewed by Freudians as a worthwhile goal of therapy it is not obvious that this should be the case. If someone can clearly recall a painful memory then the recall is bound to cause many of the same painful emotional reactions that the original incident caused. Well, why put oneself through the same experience again? Isn't there a lot of advantage to making painful memories hard to access in order to reduce the likelihood of being reminded of them?

Debriefing after a traumatic event has been called into question as a useful method for counseling the victims of traumatic experiences. It may well be that debriefing doesn't work because it causes the mind to go over the traumatic events and therefore it may strengthen memory formation and later painful recall.

Perhaps what is needed is the ability to place removable blocks on memories. I'm thinking of something along the line of the ability to recall past memories when it becomes critical to do so. If any of you have read Roger Zelazny's Today We Choose Faces then imagine the ability to recall past memories of past clones without having to die in order to do so. One could even place tags on memories explaining why one might want to peer into them. For instance, a person thinking of remarrying might want to gain better access to memories of what went wrong in a previous marriage. Or on an anniversary date of the death of a loved one one might want to make the memories of time spent with that person more accessible.

The Stanford researchers were working with very new memories. But in rats the protein synthesis inhibitor anisomycin has been successfully used to erase 45 day old memories See the previous post Consolidated Memories Are Erasable In Rats.

Share |      Randall Parker, 2004 January 09 04:58 PM  Brain Memory

sal said at August 30, 2005 11:45 PM:

I wonder why some people can't remember nearly all of their childhood, I have come across such people in the past.They hardly remember anything.Just small pieces of memories, broken memories.

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