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Neuroscientists have discovered that long-term memories are not etched in a "clay tablet"-like stable form as once thought. The process is much more dynamic, involving a miniature molecular machine that must run constantly to keep memories going, and jamming this machine briefly can erase long-term memories.

The findings by Prof. Yadin Dudai, Head of the Weizmann Institute’s Neurobiology Department, which appeared today in the journal Science, may pave way for memory altering drugs in the future.

Dudai and his team trained rats to avoid certain tastes and then injected a drug to block a specific protein into the taste cortex – an area of the brain associated with taste memory.

They hypothesized, that this protein, an enzyme located in the synapses called PKMzeta, acts as a miniature memory “machine” that keeps memory up and running by changing some facets of the structure of synaptic contacts.

But it must be persistently active to maintain this change, which is brought about by learning.

Silencing PKMzeta, reasoned the scientists, should reverse the change in the synapse.

They proved their hypothesis by showing that regardless of the taste the rats were trained to avoid, they forget their learned aversion after a single application of the drug.

The technique worked as successfully a month after the memories were formed, which is analogous to years in humans, and all signs so far indicate that the affected unpleasant memories of the taste had indeed disappeared.

This is the first time that memories in the brain were shown to be capable of erasure so long after their formation.

“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 and these findings raise the possibility of developing a "memory eraser".