Long term memories are believed to be represented in the brain using synapses. Synapse is a connection between two neurons. When two neurons are connected with a synapse electrical activity of the first neuron will affect the other neuron's electrical activity. Using complicated wiring of neurons the synapses in our brain link visual images, sounds and any other input data to a specific learned knowledge. For instance, when we learn to recognize new face we create new synapse between neurons in our brain. The Weizmann research tried to determine whether the synapses are stable once created or should be maintained constantly. 

The research shows that by blocking the enzyme PKMzeta long term memories of a rat are erased. The researchers, headed by Professor Yadin Dudai, trained rats to avoid a certain taste and after a week (or a month in a different group) treated the rats with ZIP, a PKMzeta inhibitor. The rats treated with ZIP forgot what they learned and ate the food while rats in the control group kept avoiding it. According to the scientists, this proves that PKMzeta has a role in keeping long term memories viable. 

What makes inhibition of the PKMzeta erase memories is not yet known. However, the conclusion from the experiment is that the synapses are constantly maintained and by stopping this maintenance the synapse weakens. This research opens new paths for further researches involving learning and memory; it puts the science one step ahead in understanding and finding a cure to dementia and other memory related diseases.

More information can be found on the on Weizmann institute website, and in Science magazine (subscription required).