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Thursday, Jan. 22, 2004

NATURAL SELECTIONS

Out of thought, out of mind


Sigmund Freud was well aware that his theories were controversial. "What progress we are making," he commented in 1933. "In the Middle Ages they would have burned me. Now they are content with burning my books."

As it happened, four years later the new authorities in Vienna weren't content with just burning his books and Freud had to flee into exile in London. The Nazis had annexed Austria and as a Jew there was a very real threat to his life.

Freud's books might not be burned anymore, but his work has remained controversial. However, research published in Science earlier this month suggests for the first time that there is a biological basis for one of Freud's central ideas. Could we have a Freudian renaissance in the 21st century?

Psychotherapy would welcome it: It's had a rough time recently. Particularly troubling were scandals in the United States and Britain concerning the recovery of repressed memories. In the 1990s, thousands of people in therapy -- mostly young women -- suddenly recovered memories of childhood sexual abuse.

After the initial shock, people started asking whether these "memories" might be false. A new term for the phenomenon was quickly coined: "false memory syndrome," but irreparable damage had been done to thousands of family relationships. Lawyers were the only beneficiaries.

But then researchers, like Michael Anderson, a psychology professor at the University of Oregon, started wondering whether memories can be suppressed at all. And if so, can it be shown scientifically?

The way Freud saw it, the mind has defense mechanisms, the most important of which is repression, which banishes unwanted memories and feelings into the unconscious. For example, according to Freud, the mind represses a child's sexual feelings toward the parent of the opposite sex.

Whether or not one believes that a child has such feelings in the first place, one reason Freud's theory of repression has been controversial is because it has lacked a scientific basis. What Anderson and colleagues have now done is determine that the brain does have a way to block unwanted memories. The results have astounded neurologists because it seems that the unwanted memories are suppressed using brain areas similar to those used when we try to stop overt physical actions.

Like so many new discoveries about the brain, the breakthrough has been made possible by functional magnetic resonance imaging (fMRI). This remarkable process produces images of the brain which allow researchers to determine which parts of the brain are in use for different tasks.

Twenty-four people, ages 19 to 31, were scanned for the experiment. Participants were given 36 pairs of nouns, such as "ordeal-roach," "steam-train" and "jaw-gum," and asked to remember them at 5-second intervals.

Then, while laying down inside the fMRI scanner the subjects were given the first member of a word pair and asked either to think of the second word, or to suppress awareness of the second word. Some of the word pairs -- called baseline pairs -- weren't given while the subjects were in the scanner.

After the experiment, the subjects' memories were tested. 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 half an hour.

And the fMRI images 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 the frontal cortex was activated during the experiment, the better the subject was at repressing unwanted memories.

Anderson likened the brain's ability to control memory to an individual's reflexive ability to halt an unwanted action. For example, he recalled once noticing a potted plant starting to fall from a windowsill. He moved to catch the plant until he realized it was a cactus and withdrew his hand at the last moment. "Our ability to stop action is so ubiquitous we don't know we're doing it," Anderson said. "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."

So the brain systems that permit one to stop an arm motion midway can be recruited to inhibit or stop an unwanted memory retrieval. Instead of inhibiting activity in brain regions having to do with physical action, however, these control processes reduce brain activation in the hippocampus, a structure known to be involved in conscious memories of the past. Crucially, this reduction in hippocampal activity led the subjects to forget the rejected experiences.

"It's amazing to think that we've broken new ground on this -- that there is a clear neurobiological basis for motivated forgetting," Anderson said. "Repression has been a vague and controversial construct for over a century, in part because it has been unclear how such a mechanism could be implemented in the brain. The study provides a clear model for how this occurs by grounding it firmly in an essential human ability -- the ability to control behavior."

Coauthor John Gabrieli, psychology professor at Stanford University, Calif., acknowledged the Freudian nature of the new work. Freud argued that even if people can repress unwanted memories, they can still exert an influence. "It's lurking in them somewhere," Gabrieli said, "and it has consequences even though they don't know why in terms of their attitudes and relationships."

Rowan Hooper is a researcher at Trinity College Dublin. He welcomes comments at rowan.hooper@tcd.ie


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