The courtroom tales were lurid and, in hindsight, difficult to believe. Satanic sacrifices of babies, forced sex with animals, torture and sexual abuse of infants and young children. Victims came forward as adults, saying they had recovered forgotten memories of terrible events that had occurred in their childhood.
When the first criminal cases involving repressed memories made headlines in the United States in the 1980s and early '90s, the shocking recollections were accepted as legitimate.
But many scientists were skeptical, and soon established the fallibility of recovered memories, which can be brought on by suggestions from a therapist. The idea that all recovered memories were real memories was discredited, and the notion that many are false or pseudo-memories gained wide acceptance.
Some have argued that there is no such thing as a repressed memory.
That's going too far, says Michael Anderson, a neuroscientist at the University of Oregon. This week, he reported on what happens in the brain when people try not the think about something, what he describes as the biological mechanism for repression.
"Repression has been a vague and controversial construct for over a hundred years, in part because people can't imagine how it would work in the brain," he says.
Dr. Anderson expects his findings, published this week in the journal Science, will spark criticism and debate because they provide physical evidence that repressed memories may be real. "This is an intensely polarized debate and there are people who are going to be unhappy with any evidence that suggest repression exists," he says.
"My motive is to try to understand a model and a set of tools by which people can achieve an understanding of the act of forgetting," he says. "Can we develop rigorous scientific techniques to look at active forgetting. Might it exist? What properties does it have? What are its limits?"
The idea that we can repress memories has been controversial since it was first proposed by Sigmund Freud a century ago. Dr. Anderson believes that his findings support the psychoanalyst's theory that a person can voluntarily suppress memories. He says he is not talking about unconscious repression, where something horrible happens to you, and zap, suddenly you don't remember it any more.
Dr. Anderson's work is on the deliberate act of forgetting, something he says occurs almost daily in all of our lives. For example, you are trying to fall asleep, but are upset about a fight you had with a neighbour. You force it out of your mind, and eventually forget it.
Repressing a memory doesn't have to involve something traumatic: You change the security code on your voice-mail. For a few weeks, you punch in the old one by mistake. Then, gradually, you forget the old code. If someone asks you for it months later, you probably will be unable to recall it.
Many neuroscientists are obsessed with figuring out how memories are formed, believing memory is the key to understanding the human brain. A handful, including Dr. Anderson, are fascinated by how we forget, how the brain erases memories of what you ate for lunch every day last year or more traumatic memories of an accident or a violent crime.
Dr. Anderson's earlier work found that people are more likely to forget a series of words they have memorized if they make a deliberate attempt not to think about them.
In those experiments, volunteers were asked to memorize 50 pairs of words that were loosely connected to each other, such as jaw and gum. Then, researchers showed participants some of the words, and requested that they not think about their matches. With other words, the researchers asked the participants to think about the matching word.
Later, tests showed that the volunteers could not remember a significant number of the words they had tried not to think about, even when they were given clues or offered money to do so. They did much better remembering the words they had thought about.
Dr. Anderson recently performed the same experiment, but used sophisticated imaging equipment to take pictures of participants' brains as they tried not to think about words.
He found that when the volunteers were trying not to think of a particular word, there was less activity in their hippocampus, a part of the brain that is essential for forming new memories.
More intriguingly, he found that part of their prefrontal cortex used to inhibit physical movements was activated. That's the same part of the brain at work when you reach for a pot on the stove, but stop seconds before you touch it because it might be hot. It makes sense, he argues, that the part of the brain that inhibits physical movements would also inhibit thoughts.
His study looked at a specific phenomenon: how deliberately not thinking about a particular word leads to difficulty remembering it. But he believes that the brain activity he observed in his experiment may also be involved in suppressing traumatic memories of early-childhood abuse.
Others disagree, and say Dr. Anderson is not studying repression as Freud described it.
Elizabeth Loftus is a researcher at the University of California who has done experiments showing that recovered memories may be false, and in some cases are due to suggestions from therapists working with patients to dredge up memories.
A leader in the false-memory field, Dr. Loftus says it is not clear if Dr. Anderson is studying the suppression of memory, or a different type of effort. Perhaps the volunteers were distracting themselves so they wouldn't think of the word, she says.
Her studies have shown that memories can be distorted by suggestions, and that entirely false memories can be planted in people's mind. She has been an expert witness or consultant in hundreds of trials, including the famous McMartin preschool molestation case, one of the longest and most-publicized trials in U.S. history. Children at a daycare centre in California told of strange sex rituals such as "naked movie star," and "horsy" during which ponies and parakeets were killed. There were no convictions in the case.
In her experiments, Dr. Loftus has got people to believe that they were lost for an extended period as a child or witnessed a demonic possession.
When Alan Alda, the star of the television series M*A*S*H, visited the University of California for a science show he was hosting, she convinced him that he hated eggs because he had been sickened by them as a child. (She asked him questions about his lifelong history with foods, then told him that a computer had concluded he had got sick on eggs. Later, at a picnic, he refused to eat a hard-boiled egg.)
Ira Hyman, a psychology professor at Western Washington University in Bellingham, has also done work on how false childhood memories are created. He says Dr. Anderson appears to be studying the process of inhibiting a thought, which may be different than repressing a troubling memory.
Still, he says the idea that the same parts of the brain light up when we inhibit physical actions as when we inhibit thoughts is fascinating, and worth further probing.
Dr. Hyman describes himself as a moderate in the debate over repressed memories. There are compelling case studies that people can forget a traumatic event for a long time, he says. There is also is strong evidence that shows it is very easy for people to create false memories. "Both things happen," he says. "I know of no reliable way to tell the difference."
Dr. Anderson concedes that there is no proof that the phenomenon he has been studying is what happens when people push disturbing memories out of their conscious thoughts.
But he says there is some evidence that points in that direction. There are studies that show children who were abused by a trusted caregiver are far more likely to forget the experience -- at least for a period of time -- than children who were abused by a total stranger. The children are dependent on that caregiver, and maintaining a relationship with them is essential to their survival, he says.
What intrigued Dr. Anderson, and prompted his research on repression, is that they forget the abuse even though they faced daily reminders of it -- the presence of the perpetrator. He sees this as a sign that they may have deliberately repressed the memories of abuse, perhaps in the same way the participants in his study pushed the word they had just memorized out of their minds.
He hopes that his work will provide a new tool for investigating repressed memories. But he says it might also prove useful for patients with post-traumatic stress disorder, experiencing disturbing flashbacks of violent or stressful occurrences.
Dr. Anderson is now planning a study to see if the network he has mapped out for everyday forgetting is somehow defective or disabled in the brains of people who have difficulty controlling their most troubling memories.