This 2014 human study involved the subjects replaying hippocampal memories in the limbic system while in a restful state.

The researchers found that intentional replaying made memories stronger, and improved understanding of future related material.

However, the researchers excluded emotional memories from this study. See the human Emotional memories and out-of-body–induced hippocampal amnesia study as an example of why emotional memories are necessary in order to properly study the hippocampus. Also see Problematic research on memory for why excluding emotional memories yields questionable findings.

http://www.pnas.org/content/111/44/15845.full “Memory reactivation during rest supports upcoming learning of related content”