The discovery opens up the possibility of memories being blocked or altered using the beta-blocker propranolol, which is already being used to treat migraines, anxiety and heart conditions.
Scientists in New York have had some success with the beta-blocker in 2004 when they were teaching lab rats how to forget a learned trauma.
However, the results have been difficult to reproduce.
Lead researcher Amy Milton and her team have now found if the shank protein is degraded, memories may become modifiable.
But if the protein is present, then chances are the memories are not degradable, which could explain why the propranolol did not work.