Reactivating a specific memory does not affect associated or related memories

Feb 16 2006

Researchers at a trio of universities have found that reactivating a specific memory does not affect associated or related memories, adding to our understanding of how memories are stored and influenced. The study appears in the latest issue of the Proceedings of the National Academy of Sciences.

The study's authors are Jacek Debiec and Joseph LeDoux of New York University's Center for Neural Science, Valirie Doyhre of NYU and Universiti Paris-Sud, and Karim Nader, a psychology professor at McGill University.

Memories are made in stages. These initial stages involve learning followed by consolidation--a process during which the memory trace is formed. Unconsolidated memories are susceptible to disruption. Therefore, various pharmacological agents or interfering tasks applied before consolidation occurs prevent a memory from persisting. However, once consolidation occurs, memories may be long lasting--one experience may create memories that last a lifetime.

For years it had been believed that consolidated memories were resistant to drug manipulations, which are effective in the early stages of memory formation. However, increasing number of data indicate that reactivation of consolidated memories renders them susceptible to treatments, which may result in either impairment or enhancement of the reactivated memory. This process is often referred to as reconsolidation, which has been proposed as a possible way of treating traumatic memories. Yet, several concerns have been raised that reactivating and disrupting a single memory may also affect other associated memories. Debiec and colleagues found that only directly but not associatively reactivated memories are vulnerable to disruption.

The researchers investigated this process by testing laboratory rats. After demonstrating the presence of associated memories in the rats, the researchers tested how the reactivation of a single memory--in this case, the rats' response to a mild electric shock that followed an audio tone--affected associated memories. They found that while the reactivated memory became subject to disruption, associated memories were not affected.

Experimental studies showing that reactivation of existing memories makes them susceptible to pharmacologic interventions raised hopes that reconsolidation may be used to treat debilitating traumatic memories, such as those that occur in post-traumatic stress disorder. However, several concerns have been raised. One of the most common worries is that manipulating with the reactivated memory may also affect other associated memories. The current study demonstrates that in animal models only directly reactivated but not associated memories are vulnerable to disruption. If confirmed in humans these results may the pave the way to developing novel treatments of intrusive traumatic memories.