A daytime nap does not increase pattern separation ability

Introduction

A large body of studies has showed that the ability to learn new information is impaired when we are sleep deprived. Pattern separation (PS), the ability to form distinct memories for events that are highly similar and share overlapping features, has also previously been found to be impaired by sleep deprivation. In the present study, we examined if a daytime nap would increase PS performance.

Methods

108 young healthy participants came to the lab in the morning and completed the Mnemonic Similarity Task (MST). This task starts with an encoding phase where participants view images of common everyday objects and are asked to classify them as indoor or outdoor objects. During a subsequent memory test, participants view three different kinds of objects; ‘old’ objects that were also present during the encoding phase, ‘new’ objects that have not been seen before, and ‘lure’ objects that are similar to, but not exactly the same as, objects viewed during encoding. The task of the participants during the re-test is to say if the objects presented are ‘old’, ‘new’ or ‘similar’. This test gives two different outcome measures: General Recognition (GR) - the ability to separate old objects from new ones, and PS - the ability to separate similar objects from old ones. After this task, participants were randomly allocated to either a sleep or a wake group. The sleep group had a two-hour nap opportunity and the wake group spent an equal amount of time resting. After this delay interval, participants completed the MST for a second time with a new set of images.

Results

Results revealed no support for sleep in increasing either GR or PS ability. Within the sleep group, there were no correlations between changes in PS ability and time spent in any sleep stage.

Conclusion

Previous studies that have found a role of sleep for PS ability has done so using larger manipulation of sleep. Based on the present study however, just a short daytime nap does not seem to have any effect on PS ability.