Experiment supports Freud's theory of repression


Wednesday, March 14th 2001, 12:00 am
By: News On 6


An experiment found that people can push an unwanted memory out of their minds, lending credence to Sigmund Freud's theory of repression.

In the study, college students who had memorized pairs of words were later shown half of the pair and were asked to either say the corresponding word or try to forget the second word.

The more the participants were asked to put words out of their minds, the less likely they were to recall the word later, even when paid to remember the word.

The University of Oregon study is one of two on memory appearing in Thursday's issue of the journal Nature. In the second study, which was conducted on rats, researchers found that the growth of new neurons in a part of the brains known as the hippocampus is necessary to form memories relating two events separated over time.

Martin Conway, a psychologist at the University of Bristol in England, said in an accompanying commentary that the Oregon research supports Freud's theory about the mind's ability to repress thoughts, especially painful or disturbing ones.

``Even more surprising is that this occurs for unrelated pairs of words,'' Conway said. ``How much stronger must this inhibition be for objects central to our thoughts and emotions.''

Michael Anderson, who led the study of 32 students, said the participants were about 10 percent less likely to remember the second word after 16 attempts to repress the memory, a figure he said he expected would climb if repression continued.

The work supports the findings of a colleague who found that children were less likely to remember abuse at the hands of a parent or guardian than a stranger, possibly because they had to forget in order to be able to cope with their daily routine, Anderson said.

However, the researcher admitted that memorizing word pairs is far from the type of memory associated with painful events such as child abuse.

``What we really need to do is see if the same effect occurs for emotionally more significant material,'' Anderson said. ``That's a very important step we have to take. I wouldn't really say we've solved the repression problem here. It's just a good start.''

In the rat study, Tracey Shors of Rutgers University said rats were not as likely remember the connection between two events separated by time if given a drug that cuts the production of neurons in the hippocampus, an area of the brain used in the formation of some types of memory.

Eighteen rats were given the drug.

The brains of both rats and humans have a hippocampus, and the study is the first to show in mammals that new neurons are used in memory formation, though previous work has shown the connection in birds, Shors said.

Shors said previous work has shown that the learning of certain tasks made cells in the hippocampus live longer. The current work found that these cells are needed for some types of memory.

Jeffrey Mackliss, a neurobiologist at Harvard Medical School, said the experiment supports both the concept that the production of neurons is necessary for some types of memory formation and the idea that it may one day be possible to treat some diseases of the nervous system with neurons.