It’s now well established that sleep plays an important role in memory and learning. Now a new study suggests that dreams also play a part in consolidating memories. The study involved 99 subjects training for an hour on a computerized maze task, and then either taking a 90-minute nap or engaging in quiet activities. Intermittently, subjects were asked to describe what was going through their minds, or what they had been dreaming about. Five hours after training, the subjects were retested on the maze task. While those who hadn’t slept showed no improvement on the second test (even if they had reported thinking about the maze during their rest period), and those nappers who reported no maze-related dreams also showed little improvement, those who dreamed about the task showed dramatic improvement. Those who dreamed about the task were not more interested or motivated, but they were more likely to have performed relatively poorly during training — suggesting that the sleeping brain is more likely to focus on areas of greatest need. The researchers believe not that dreaming causes you to remember, but that dreaming is a marker that the brain is working on a problem at many levels — perhaps reflecting the brain's attempt to find useful associations.
Dreams are the brain's way of communicating important memory functions
 Dreaming of a Learning Task Is Associated with Enhanced Sleep-Dependent Memory Consolidation. Current Biology. 20(9), 850 - 855.(2010).