Notre Dame psychologist Jessica Payne and colleagues studied 207 students who habitually slept for at least six hours per night. Participants were randomly assigned to study declarative, semantically related or unrelated word pairs at 9 a.m. or 9 p.m., and returned for testing 30 minutes, 12 hours or 24 hours later. Declarative memory refers to the ability to consciously remember facts and events, and can be broken down into episodic memory (memory for events) and semantic memory (memory for facts about the world). People routinely use both types of memory every day — recalling where we parked today or learning how a colleague prefers to be addressed.

“Our study confirms that sleeping directly after learning something new is beneficial for memory. What’s novel about this study is that we tried to shine light on sleep’s influence on both types of declarative memory by studying semantically unrelated and related word pairs,” Payne says.

“Since we found that sleeping soon after learning benefited both types of memory, this means that it would be a good thing to rehearse any information you need to remember just prior to going to bed. In some sense, you may be ‘telling’ the sleeping brain what to consolidate.