In the Neuron article, Dr. Nader and his colleague from New York University extended this work to the part of the memory system that contributes to mediating conscious or declarative memories, called the hippocampus. They conditioned rats to fear the environment in which they were (i.e. a small box) by inducing a light electric shock on their paws.
This paradigm engaged the hippocampus to process information about the context that can be used to predict shock. The hippocampal contributions to this paradigm are thought to engage similar processes as declarative memories in humans. "According to the cellular theory of memory, new memories require new protein synthesis to be stored," explains Dr Nader.
"The hippocampus also has a second level of consolidation called systems consolidation theory. This posits that the hippocampus has a time-limited role in memory storage, after which the memory is independent of the hippocampus. This is why amnesiacs such as H.M. (the patient of neuropsychologist Brenda Milner) who have damage to their hippocampus can remember events that happened a few years ago but can't remember recent events."
Before testing cellular reconsolidation in the hippocampus, professors Nader and Ledoux showed that intra-hippocampal infusions of the protein synthesis inhibitor anisomycin caused amnesia for a consolidated hippocampal-dependant contextual fear memory, but only if the memory was reactivated prior to infusion. "This demonstrated that memories stored in the hippocampus can undergo cellular reconsolidation or restorage," said Dr. Nader. "Surprisingly, the effect occurred even if reactivation was delayed for 45 days after training, a time when declarative memory is independent of the hippocampus. In fact, we found that if you lesion the hippocampus 45 days after conditioning, there is no effect. Therefore the memory of the context has to be independent of the hippocampus. However, if the memory is now reactivated immediately prior to lesions, there is a large effect. Thus, mature old memories stored in our cortex return to being dependent on the hippocampus after they are reactivated, an instance of systems reconsolidation."
Consider the implications if this can be made to work for humans. Traumatic memories could be erased. Is that good or bad? It seems a scary prospect. But also memories of crime could be erased and a perpetrator could claim in all honesty to have no memory of having committed a particular act. Even more nefarious uses of such a technique could be imagined. A criminal or a government could force someone to recall a memory that they don't want a person to have and then erase it.
|Share |||Randall Parker, 2003 January 04 02:08 PM Brain Memory|