An hour-long nap may improve associative memory performance. Associative memory is a memory of a past event or place that occurs by recalling something associated with it. Associative memory also refers to retrieval of a memory in relation to the presentation of an associated stimulus of it. Sara Studte, from Saarland University (Germany), and colleagues enrolled 41 adult students in a study in which each participant learned single words and word pairs. Once the learning phase was over, the subjects were tested to determine how much information they could remember. About half of the participants were then allowed to take a nap (90 minutes duration), while the others watched a DVD. Afterwards, all subjects were retested. The participants who took a nap were shown to have retained substantially more word pairs in memory, as compared to the subjects who watched a DVD and did not nap. Reference: Sara Studte, Emma Bridger, Axel Mecklinger. “Nap sleep preserves associative but not item memory performance.” Neurobiology of Learning and Memory, Volume 120, April 2015, Pages 84-93.