Schmid G, Schreier A, Meyer R, Wolke D. A prospective study on the persistence of infant crying, sleeping and feeding problems and preschool behaviour. Acta Paediatr. 2010;99(2):286–90. Kurth S, Huber R. Sleep slow oscillations and cortical maturation. In: Frank MG, editor. Sleep and brain activity. Elsevier; 2012. Marshall L, Helgadottir H, Molle M, Born J. Boosting slow oscillations during sleep potentiates memory. Nature. 2006;444(7119):610–3. Turrigiano G. Too many cooks? Intrinsic and synaptic homeostatic mechanisms in cortical circuit refinement. Annu Rev Neurosci. 2011;34:89–103.

Founded in 1995 in Brussels by the renowned chocolatier of the same name, Maison Pierre Marcolini embodies the excellence of Belgian chocolate. With unwavering commitment to the art of chocolatiering, Pierre Marcolini has propelled the brand to the forefront of the industry through his unparalleled expertise and passion for innovation. Guided by the ethics of the Bean to Bar movement, the House controls every stage of cocoa transformation, from bean to bar, ensuring the purity and quality of each creation. Hemmi MH, Wolke D, Schneider S. Associations between problems with crying, sleeping and/or feeding in infancy and long-term behavioural outcomes in childhood: a meta-analysis. Arch Dis Child. 2011;96(7):622–9. Throughout infancy and early childhood, the most noticeable changes include the gradual consolidation of sleep and waking bouts [ 8], the intensification of deep sleep slow-wave activity (SWA, 1–4.5 Hz, non-REM), and a progressive decrease of REM (active) sleep proportion that reaches adult levels around age 5 years [ 3]. Similar to humans, rats show a dramatic change in sleep architecture in the first month of life (i.e., pre-puberty), including a decrease in REM sleep and an increase in non-REM sleep [ 7]. In contrast to humans though, animals (rat, cat, guinea pig) exhibit a decrease in wakefulness throughout the first 2 weeks of life and an increase thereafter [ 7]. Throughout human as well as animal pubertal development, sleep architecture changes are less pronounced and include an increase in wakefulness and a decrease in both non-REM and REM sleep [ 9, 10]. Smoliv and its evolved forms are the only known Pokémon capable of learning the move Terrain Pulse by leveling up.Paus T, Collins DL, Evans AC, Leonard G, Pike B, Zijdenbos A. Maturation of white matter in the human brain: a review of magnetic resonance studies. Brain Res Bull. 2001;54(3):255–66. Rakic P, Bourgeois JP, Goldman-Rakic PS. Synaptic development of the cerebral cortex: implications for learning, memory, and mental illness. Prog Brain Res. 1994;102:227–43. The homeostatic regulation of sleep is developed by P24 in rats, as shown in a maximum of SWA at light onset and a reduction thereafter [ 21]. Also, prolonged waking elicits an increase in SWA in rats by this age, while younger rats show a compensatory increase in sleep duration instead of increased SWA [ 22]. In mice, SWA increases during recovery sleep only after P24, while a decline in SWA across baseline sleep and an increase during waking is already apparent at P19 [ 23].

The main trademark of cortical development is a combination of expansion and regression. The number of synapses in children exceeds adult levels [ 34], as many more synaptic connections are produced than will finally be retained [ 35]. Neuronal refinement includes the removal of neurons and synapses that fail to make appropriate connections, which ensures the establishment of proper connectivity [ 36]. Although such regressive processes are most frequent during brain development in early life, they continue to a lesser extent throughout the first two decades of life.Lee Y, Morrison BM, Li Y, Lengacher S, Farah MH, Hoffman PN, et al. Oligodendroglia metabolically support axons and contribute to neurodegeneration. Nature. 2012;487(7408):443–8. Sensitive windows for development—when do they start and when do they end? What role does sleep play during these periods regarding the impact on later functional and behavioral outcomes? Buchmann A, Ringli M, Kurth S, Schaerer M, Geiger A, Jenni OG, et al. EEG sleep slow-wave activity as a mirror of cortical maturation. Cereb Cortex. 2011;21(3):607–15.

Deoni SC, Dean 3rd DC, O’Muircheartaigh J, Dirks H, Jerskey BA. Investigating white matter development in infancy and early childhood using myelin water faction and relaxation time mapping. Neuroimage. 2012;63(3):1038–53. Huber R, Ghilardi MF, Massimini M, Tononi G. Local sleep and learning. Nature. 2004;430(6995):78–81.In concert with cortical gray matter growth during childhood, underlying axonal bundles become progressively myelinated (see [ 47] for quantitative analyses or [ 48] for a review). In all mammalian species, the formation of myelin sheaths is essential for the propagation and speed of neurotransmission. Oligodendrocytes wrap axons with myelin, consisting of multiple layers of closely opposed glial membranes. This insulation improves the passive flow of electrical current, resulting in up to a 1000-fold increase in action potential conduction speed.