Beneficial effects of sleep for memory consolidation

Offline consolidation of memory varies with time in slow wave sleep and can be accelerated by cuing memory reactivations.
Diekelmann S, Biggel S, Rasch B, Born J.
Neurobiology of Learning and Memory Volume 98, Issue 2, September 2012, Pages 103–111

Memory representations are reactivated during slow-wave sleep (SWS) after learning, and these reactivations cause a beneficial effect of sleep for memory consolidation. Memory reactivations can also be externally triggered during sleep by associated cues which enhance the sleep-dependent memory consolidation process. Here, we compared in humans the influence of sleep periods (i) of 40min and (ii) of 90min without externally triggered reactivations and (iii) of externally triggered reactivations by an associated odor cue during a 40-min sleep period on the consolidation of previously learned hippocampus-dependent visuo-spatial memories. We show that external reactivation by an odor cue during the 40-min sleep period enhanced memory stability to the same extent as 90min of sleep without odor reactivation. In contrast, 40min of sleep without external reactivations were not sufficient to benefit memory. In the 90-min sleep condition, memory enhancements were associated with time spent in SWS and were independent of the presence or absence of REM sleep. These results suggest that the efficacy of hippocampus-dependent memory consolidation depends on the duration of sleep and particularly SWS. External reactivation cues can accelerate the consolidation process even during shorter sleep episodes.

Spatial and contextual memories

Sleep modulates the neural substrates of both spatial and contextual memory consolidation.
Geraldine Rauchs, Pierre Orban, Christina Schmidt, Genevieve Albouy, Evelyne Balteau, Christian Degueldre, Caroline Schnackers, Virginie Sterpenich, Gilberte Tinguely, Andre Luxen, Pierre Maquet, Philippe Peigneux
PLoS ONE 2008;3(8):e2949.

Background: It is known that sleep reshapes the neural representations that subtend the memories acquired while navigating in a virtual environment. However, navigation is not process-pure, as manifold learning components contribute to performance, notably the spatial and contextual memory constituents. In this context, it remains unclear whether post-training sleep globally promotes consolidation of all of the memory components embedded in virtual navigation, or rather favors the development of specific representations.

Methods: Here, we investigated the effect of post-training sleep on the neural substrates of the consolidation of spatial and contextual memories acquired while navigating in a complex 3D, naturalistic virtual town. Using fMRI, we mapped regional cerebral activity during various tasks designed to tap either the spatial or the contextual memory component, or both, 72 h after encoding with or without sleep deprivation during the first post-training night.

Results: Behavioral performance was not dependent upon post-training sleep deprivation, neither in a natural setting that engages both spatial and contextual memory processes nor when looking more specifically at each of these memory
representations. At the neuronal level however, analyses that focused on contextual memory revealed distinct correlations between performance and neuronal activity in frontal areas associated with recollection processes after post-training sleep,
and in the parahippocampal gyrus associated with familiarity processes in sleep-deprived participants. Likewise, efficient spatial memory was associated with posterior cortical activity after sleep whereas it correlated with parahippocampal/
medial temporal activity after sleep deprivation. Finally, variations in place-finding efficiency in a natural setting encompassing spatial and contextual elements were associated with caudate activity after post-training sleep, suggesting
the automation of navigation.

Conclusion: These data indicate that post-training sleep modulates the neural substrates of the consolidation of both the spatial and contextual memories acquired during virtual navigation.