Scientists at the University of Pennsylvania have shown that memories are not as fluid as current research suggests.
Their findings challenge the prevailing notion on how memories are stored and remembered or that a recalled memory could be altered or lost as it is "re-remembered."
Previous experiments with anisomycin helped lead to the acceptance of a theory in which a learned behavior is consolidated into a stored form and that then enters a 'labile' or 'adaptable' state when it is recalled.
According to these previous studies, the act of putting a labile memory back into storage involves a reconsolidation process identical to the one used to store the memory initially.
Indeed, experiments showed that anisomycin could make a mouse forget a memory if it were given anisomycin directly after remembering an event.
In the study, however, the Penn researchers showed that disruption of a "re-remembered" memory was not permanent.
"When we looked at mice 21 days after they were treated with anisomycin to block the reconsolidation of a memory, we showed that they could, in fact, remember the original learned behavior," K Matthew Lattal, a postdoctoral researcher in Penn's
Department of Biology and a co-author of the study said.
"If you use the anisomycin, you can destroy a 'fresh' memory, but the 'forgetting' effect of anisomycin on an established memory is only temporary, at best," he added.
According to the researchers, the prominent theory of how memories are stored cannot account for the return of a supposedly forgotten memory. Accounting for the temporary loss of memories following the act of remembering will require further study.
"Whatever molecular mechanism occurs as a memory is being put back into storage, it allows the original memory to remain unaffected," said Ted Abel, an assistant professor in Penn's Department of Biology and co-author of the study. "Ultimately,
'reconsolidation' might not be an accurate portrayal of what is
Memory-related illnesses, such as post-traumatic stress disorder, would undoubtedly benefit from a more accurate understanding of the molecular events behind memory storage.