From Science Daily -
"Are memories recorded in a stable physical change, like writing an inscription permanently on a clay tablet?"
"Dudai and research student Reut Shema, together with Todd Sacktor of the SUNY Downstate Medical Center, trained rats to avoid certain tastes. They then injected a drug to block a specific protein into the taste cortex -- an area of the brain associated with taste memory. They hypothesized, on the basis of earlier research by Sacktor, that this protein, an enzyme called PKMzeta, acts as a miniature memory "machine" that keeps memory up and running. An enzyme causes structural and functional changes in other proteins: PKMzeta, located in the synapses -- the functional contact points between nerve cells -- changes some facets of the structure of synaptic contacts.
It must be persistently active, however, to maintain this change, which is brought about by learning. Silencing PKMzeta, reasoned the scientists, should reverse the change in the synapse. And this is exactly what happened: Regardless of the taste the rats were trained to avoid, they forget their learned aversion after a single application of the drug."
("This drug is a molecular version of jamming the operation of the machine," says Dudai. "When the machine stops, the memories stop as well." In other words, long-term memory is not a one-time inscription on the nerve network, but an ongoing process which the brain must continuously fuel and maintain. These findings raise the possibility of developing future, drug-based approaches for boosting and stabilizing memory.)