Sleep and memory go hand in hand. Memory is a skill for surviving, and while we use it during the awaken states, we file and store during sleep.
Tabula rasa can be a paradox if we are considering developed creatures, for that implies one has no memory of anything. Ed Parkins's documentary Tell Me Who I Am touches on the idea that memory loss can be the loss of everyting you have learned up until the event preceeding the loss and that one can become tabula rasa as an adult. What is striking is that the lost memory will never be available to you again, sort of a hardware damage that is actually an organic damage to the brain.