Researchers from Stanford and the University of Oregon have shown that the human brain is capable of voluntarily repressing unwanted memories, a concept that was introduced by Sigmund Freud more than 100 years ago.

The results were published this month in a paper titled “Neural Systems Underlying the Suppression of Unwanted Memories,” co-authored by Psychology Prof. John Gabrieli, in the journal Science. Gabrieli studies the brain basis of how human memory is made and forgotten. He researched repression as one example of voluntary, willful forgetting.

“Our research supported that view that the brain mechanisms we understand quite a bit about . . . can support an example of repression,” Gabrieli said.

The experiment — conducted at Stanford last year — not only demonstrated the human capability to repeatedly block unwanted thoughts until they can no longer remember them, but also specified which brain regions supported this practice.

The idea of repressed memories is a topic that has been debated among laymen and scientists alike for over a century. The first controlled experimental evidence that memory repression does exist was published three years ago in Nature by the recent paper’s lead author Michael Anderson, an associate professor of psychology at the University of Oregon. Anderson and Gabrieli have now built on that research by showing the brain’s capacity to repress memory and how it is implemented.

“Repression has been a vague and controversial construct for over a century,” Anderson told The Stanford Report. “The study provides a clear model for how this occurs by grounding it firmly in an essential human ability — the ability to control behavior . . . This idea is that the neurobiological mechanism that we have evolved to control overt behavior might be recruited to control internal actions such as memory retrieval as well.”

In the experiment, 24 people were given 36 pairs of nouns and were tested on their memory of them until they answered about three-fourths correctly.

They were then tested while using functional magnetic resonance imaging to scan their brains. Researchers divided the word pairs into three sets. For the first set, they asked subjects to look at the first word of the pair and recall and think of the second word, and for the second set, they asked them not to recall or think of the second word. Then, subjects were retested on all of the word pairs and researchers discovered that subjects remembered fewer of the word pairs in the set they had actively tried not to think about than in the third, baseline, set of pairs that they had not seen during the 30-minute brain scanning portion of the experiment.

“People’s memory gets worse the more they try to avoid thinking about it,” Anderson said to The Stanford Report. “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 researchers identified the systems in the brain that play a role in actively suppressing memory using the fMRI scans. Specifically, they showed a connection between increased left and right frontal cortex activation, the part of the brain used to repress memory, and the reduced activation of the hippocampus, the part of the brain used to remember experiences. Also, they showed that subjects’ increased activation of the frontal cortex led to an improved ability to suppress unwanted memory.

Memory repression has recently become a highly controversial issue in relation to childhood sexual abuse cases because of the lack of experimental or scientific evidence that they do exist and are not just false memories. Gabrieli said that their research has limited implications for the subject, though, because the experiment tested healthy volunteers using neutral words in a very different situation from sexual assault occurrences.

The research opens the field for more exploration of memory repression, according to Gabrieli. For example, researchers can now test whether these findings also apply to emotionally salient experience by using more emotionally powerful stimuli in healthy people.

Another interesting extension would be to research the capacity of memory suppression in people who want to repress memories and cannot — for example, people who are depressed and dwell too much on negative experiences or post-traumatic stress disorder patients who remember traumatic experiences all too well.