Reposted From Ingenious Monkey:

Whether it be language acquisition, motor skill learning, or spatial association: Sleep is an integral part of memory consolidation and how our brain processes newly acquired information.
The effect of sleep is generally one of improved memory, however there are slight differences in the relationship between sleep and memory depending on whether we are dealing with so called procedural memory (i.e. memory of a process, or of how to do something), or whether we are looking at declarative memory (basically memorization of facts). One such difference is the relative in-/sensitivity to the time frame in which sleep occurs. For procedural memory, for example, it appears that sleep will have an improving effect regardless of whether we sleep immediately after practicing a skill, or whether we catch our nap some ten hours later. Declarative memory, in contrast, seems to benefit much stronger from sleep occurring soon after acquisition of some declarative set of information. One explanation for this difference, which gets to the root of the mechanisms behind the sleep memory link, is that

"during waking, the newly formed memories are susceptible to interference by competing memory traces.[...] Interference by stimuli competing with declarative memories is thought to arise more frequently during a waking day than interference by stimuli competing with a specific new motor skill, which would provide a possible explanation for the need for sleep to occur soon after learning declarative material, but not procedural material"

What a new study in PNAS has now found is that the enhancing effect of sleep on the memory of movement, when learning by observation, is similarly dependent on an early occurrence of sleep as was usually only thought for declarative memory.
In a session of experiments involving motor skill memory, the researchers first had participants watch videos of a hand performing a finger-tapping task. Some 12 to 24 hours later - either after having slept soon after, a long time after, or not at all - participants were then made to repeat another finger tapping task which was either identical to the one in the video, or, as means of statistical control, some alternative tapping sequence.
As indicated in the below graph, participants who slept soon after viewing the video, performed substantially better at repeating the previously viewed tapping sequence, while performing identically on the alternative tapping task. Improvement occurred along the dimension of speed (22% improvement) as well as accuracy (42% lower error rate).

Proceedings of the National Academy of Sciences

In contrast, subjects who did not sleep until at least 12 hours after viewing the video showed no detectable improvement in the finger tapping task.

"In conclusion, performance enhancement through observation depends critically on subsequent sleep and is sensitive to time spent awake between learning and sleep. The effects of sleep are as pronounced as previously reported for skill learning by practice and for explicit learning paradigms. The strong dependence on immediate sleep of the enhancement of skill learning by observation suggests that it provides a valuable paradigm to elucidate the brain processes involved in the role of sleep in consolidation and enhancement of prior learning.."

The paper features three modifications of the experiment, which are meant to shed light on a number of hypotheses regarding the mechanism behind the performance benefit of relatively immediate sleep. It also offers some speculation as to linkages between their findings and the activity of mirror neurons; so you might enjoy taking a closer look at the originial also.
The study, of course, is highly relevant for situations that involve

"(re)learning movements in cases where practice is difficult or impossible, as in children, during rehabilitation following stroke or fractures, or in complex skill acquisition in, for example, sports or surgical techniques."

The studies original authors declare no conflict of interest, but I - as the author of this post - admit that I do enjoy napping after watching basketball games on tv...

Main References:

Van Der Werf YD, Van Der Helm E, Schoonheim MM, Ridderikhoff A, & Van Someren EJ (2009). Learning by observation requires an early sleep window. Proceedings of the National Academy of Sciences of the United States of America, 106 (45), 18926-18930 PMID: 19884499

About the Authors

Kimberlee D’Ardenne, Ph.D.

Kimberlee D’Ardenne, Ph.D. is a neuroscientist by training, science writer by choice.

Rachael Grazioplene

Rachael Grazioplene is a graduate student in Psychology at the University of Minnesota. Her research is focused on individual differences and behavioral genetics.

Daniel Hawes

Daniel R. Hawes is a social psychologist stuck in an applied economist's body.

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