Abstract
In adults, the synchronised interplay of sleep spindles (SP) and slow oscillations (SO) supports memory consolidation. Given tremendous developmental changes in SP and SO morphology, it remains elusive whether across childhood the same mechanisms as identified in adults are functional. Based on topography and frequency, we characterise slow and fast SPs and their temporal coupling to SOs in 24 pre-school children. Further, we ask whether slow and fast SPs and their modulation during SOs are associated with behavioural indicators of declarative memory consolidation as suggested by the literature on adults. Employing an individually tailored approach, we reliably identify an inherent, development-specific fast centro-parietal SP type, nested in the adult-like slow SP frequency range, along with a dominant slow frontal SP type. Further, we provide evidence that the modulation of fast centro-parietal SPs during SOs is already present in pre-school children. However, the temporal coordination between fast centro-parietal SPs and SOs is weaker and less precise than expected from research on adults. While we do not find evidence for a critical contribution of SP–SO coupling for memory consolidation, crucially, slow frontal and fast centro-parietal SPs are each differentially related to sleep-associated consolidation of items of varying quality. While a higher number of slow frontal SPs is associated with stronger maintenance of medium-quality memories, a higher number of fast centro-parietal SPs is linked to a greater gain of low-quality items. Our results demonstrate two functionally relevant inherent SP types in pre-school children although SP–SO coupling is not yet fully mature.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Conflict of Interest Disclosure: The authors declare no competing interests.
Data Availability: The custom code and data necessary to reproduce the results in this manuscript will be made available after acceptance of the manuscript on OSF https://osf.io/7mf9v/. During review, data and code are available from the corresponding authors upon request.
Author Notes: This research was conducted within the project “Lifespan Rhythms of Memory and Cognition (RHYME)” at the Max Planck Institute for Human Development. A-KJ is a fellow of the International Max Planck Research School on the Life Course (LIFE; http://www.imprs-life.mpg.de). MW-B received support from the German Research Foundation (DFG, WE 4269/5-1) and the Jacobs Foundation (Early Career Research Fellowship 2017–2019).
We would like to thank B. E. Muehlroth for constant advice and for providing us with her analysis pipeline and Julia Delius for editorial assistance. We are grateful to the members of the RHYME and LIME projects for helpful feedback on the analyses. We further thank all the children and their families who participated in this study.
Ethics Approval Statement: The study was designed in agreement with the Declaration of Helsinki and was approved by the local ethics committee of the Max Planck Institute for Human Development.
Permission to Reproduce Material from Other Sources: Not applicable.