A new study at Israel’s Weizmann Institute reveals the mechanism by which the brain stores memories, and may have found a way to erase unwanted memories as well.
Prof. Yadin Dudai, Head of the Weizmann Institute’s Neurobiology Department, and his colleagues are challenging the prevalent view that memories are recorded in a static, semi-permanent manner. They recently discovered that the process of storing long-term memories is much more dynamic, involving a miniature molecular “machine” that must run constantly to keep memories going. They also found that jamming said “machine” briefly can erase long-term memories. Their findings, which appeared Thursday in the journal Science, may pave the way to future treatments for memory problems.
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 (protein kinas M zeta), acts as the miniature memory “machine” that keeps memory up and running.
PKMzeta is located in the synapses – the functional contact points between nerve cells – and changes some facets of the structure of synaptic contacts.
Since the PKMzeta must be persistently active to maintain the change in synaptic contact brought about by learning, the researchers posited that silencing PKMzeta should reverse the change in the synapse.
“That is exactly what happened,” they reported. “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 (in terms of life span, more or less 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.”
Dr. Dudai says that the experiment proves that memories are not engraved, but are constantly maintained. “This drug is a molecular version of jamming the operation of the machine,” he said. “When the machine stops, the memories stop as well. Our results show that memories require continuous activity of an enzyme, and the minute that enzyme is blocked, memory may collapse. What we do with our inhibitor resembles placing a stick in the wheels of a miniature molecular machine; when the machine stops running, the taste associations that rat has learned quickly disappear.
“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…New items in memory do not consolidate into an amnesia-resistant form within hours or days after their encoding, as was thought so far, but remain sensitive to an amnesic agents long time after learning…These findings raise the possibility of developing future, drug-based approaches for boosting and stabilizing memory.”
The researchers say that the future applications of the technology may also be able to help erase memories associated with post-traumatic stress disorder.