Sleep serves disparate functions, most notably neural repair, metabolite clearance and circuit reorganization. Yet the relative importance remains hotly debated. Here, we create a novel mechanistic framework for understanding and predicting how sleep changes during ontogeny and across phylogeny. We use this theory to quantitatively distinguish between sleep used for neural reorganization versus repair. Our findings reveal an abrupt transition, between 2 and 3 years of age in humans. Specifically, our results show that differences in sleep across phylogeny and during late ontogeny (after 2 or 3 years in humans) are primarily due to sleep functioning for repair or clearance, while changes in sleep during early ontogeny (before 2 or 3 years) primarily support neural reorganization and learning. Moreover, our analysis shows that neuroplastic reorganization occurs primarily in REM sleep but not in NREM. This developmental transition suggests a complex interplay between developmental and evolutionary constraints on sleep.
Bibliographical noteFunding Information:
V.M.S. acknowledges funding from an NSF DBI CAREER Award (1254159), and G.B.W. would like to thank the NSF under the grant PHY1838420, the Eugene and Clare Thaw Charitable Trust, and Toby Shannan and CAF Canada for their generous support. Author contributions: G.B.W. and V.M.S. conceived and designed the research. J.C. performed the research, compiled the data, performed the computations, and analyzed the data. J.C., A.B.H., G.B.W., and V.M.S. developed the theory. J.C., G.B.W., and V.M.S. wrote the paper. A.B.H. helped conceive and guide neuroscience and scaling aspects of research and edited the paper. G.P. helped guide neuroscience and sleep aspects of research and edited paper. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. All data used and associated units are available at https://github.com/jycao9/Sleep.