I don't remember what Freud said about memory, except that both Freud and Plato talk about memories being repressed. Freud thought that people repressed memories of their childhood because they were traumatized. It was possible to remember these repressed memories through therapy, but essentially, although the memories were repressed, they can still affect behavior, as if some essence of them was still remembered.
This is really much different than Plato. Plato believed that all knowedge reside in the brain, but that it was forgotten through the process of childbirth. This information can be recaled if people used a method for retrieving the information, usually through rationalization. His Dialogue in Timaeus demonstrated his thought. This kind of thinking was reworked by Jung in his theory of Archetypes.