How important is sleep for a good memory?

Very important! In general, REM sleep (a deeper stage of sleep where we do a great deal of dreaming) is believed to be very important for procedural memory whereas Non-REM sleep is very important for declarative memory. As we learn more, certain stages of sleep may be more or may be less as important for memory, depending on the type of memory.

Sleep deprivation can cause cognitive deficits, including worsened memory. A study done at Michigan State University showed that students who slept more remembered more words and made fewer errors on a word recall task. The study has implications especially for older individuals, who have worse memory in general and are also more prone to false memories.

Another study done at the Beth Israel Deaconess Medical Center showed that students who had sufficient sleep were better able to perform procedural skills, such as learning to and remembering how to play music. Learning is also important for the acquisition of memory, and sleep deprivation has been shown to interfere with it, as shown in a later study done by the same group.

 In the study, participants were trained for an hour on a virtual maze task, where they were asked to learn the layout of a complex three-dimensional maze in order to learn the fastest route to the exit. After the training session, participants were either asked to take a 90-minute nap or to engage in quiet activities while awake.

When the subjects were re-tested five hours later, the subjects who did not nap did not improve on the second test, even if they reported thinking about the maze during the interlude. While the subjects who napped, but did not dream or think about the maze during the nap, also did not improve, those who did dream about the task improved dramatically.

This showed that sleep was necessary for the consolidation of information and that the dreams reflected that the brain had been busy working on the task. Notably, the subjects who dreamed about the maze did relatively poorly during training, suggesting that the brain focuses on tasks that are difficult for you during sleep, and that this sleeping state is necessary for this memory processing.