It's not clear humans could do the same, researchers say
FRIDAY, Sept. 4 (HealthDay News) -- New Swiss research suggests that young animals may have a mechanism that allows them to jettison traumatic memories, but experts say it's unclear whether humans of any age can do the same.
In fact, scientists are still debating whether human memories truly disappear or simply go into deep storage.
"It's fair to say that most of the researchers in human memory now believe that it's very unlikely memories are really erased," said Mark McDaniel, a psychology professor and memory specialist at Washington University in St. Louis. "What happens probably is that the memories are still stored."
In animals, however, there's evidence that traumatic memories that involve fear are actually erased in the young, said study co-author Cyril Herry, a researcher with the Friedrich Miescher Institute in Basel, Switzerland.
In adults, however, it seems that such memories can be blocked but still be retrieved later.
In the study, which appears in the Sept. 4 issue of Science, Herry and colleagues gave a slight shock to rats when they heard a tone. If their memory worked properly, they'd later link the two events and be afraid after hearing the tone.
In adult rats, researchers targeted what they called an extracellular matrix or "net" that seems to protects some neurons involved in memory from destruction. These cells, which are found in the brain area known as the amygdala, appear to form in the adult but not the juvenile rat.
When the researchers selectively destroyed this protective net, adult rats more rapidly forgot about the link between the tone and the sock, and completely forgot about it seven and 28 days later, suggesting that the memory had been erased, not just blocked.
But McDaniel noted that memories in humans do seem to stick around, although in some cases it may take special "cues" to bring them back into focus.
And he added that the rat research is looking at a special kind of memory called conditioning. This may work differently in humans than other kinds of memory, said McDaniel.
And what about young children? Do they erase memories like the rats? Memory research hasn't focused much on them, McDaniel said.
Herry said his findings do have possible implications for humans. According to him, more understanding about how to prevent memories from forming and sticking around in rats could help scientists figure out how to prevent unstoppable fear and anxiety in people.
Paul Sanberg, director of the University of South Florida College of Medicine's Center of Excellence for Aging and Brain Repair, agreed that's possible. "If they understand the molecular mechanism [of traumatic memories], they could maybe develop drugs to reduce symptoms in people who have pathological fear," he speculated.
Sanberg said he remains curious about one issue in all this: Why would evolution -- which preserves traits that help creatures survive -- give young animals the ability to forget traumatic events, but not older ones?
Learn more about memory from McGill University.
SOURCES: Mark McDaniel, Ph.D., psychology professor, Washington University, St. Louis; Cyril Herry, Ph.D., researcher, Friedrich Miescher Institute, Basel, Switzerland; and Paul Sanberg, Ph.D., director, University of South Florida College of Medicine's Center of Excellence for Aging and Brain Repair, Tampa; Sept. 4, 2009, Science
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