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In cognitive neuroscience, measurements of "resting baseline" are often considered stable across age and used as a reference point against which to judge cognitive state. The task-based approach-comparing resting baseline to task conditions-implies that resting baseline is an equalizer across participants and-in the case of studies of developmental changes in cognition-across age groups. In contrast, network neuroscience explicitly examines the development of "resting state" networks across age, at odds with the idea of a consistent resting baseline. Little attention has been paid to how cognition during rest may shift across development, particularly in children under the age of eight. Childhood is marked by striking maturation of neural systems, including a protracted developmental period for cognitive control systems. To grow and shape these cognitive systems, children have a developmental imperative to engage their neural circuitry at every possible opportunity. Thus, periods of "rest" without specific instructions may require additional control for children as they fight against developmental expectation to move, speak, or otherwise engage. We therefore theorize that the child brain does not rest in a manner consistent with the adult brain as longer rest periods may represent increased cognitive control. To shape this theory, we first review the extant literature on neurodevelopment across early childhood within the context of cognitive development. Next, we present nascent evidence for a destabilized baseline for comparisons across age. Finally, we present recommendations for designing, analyzing, and interpreting tasks conducted with young children as well as for resting state. Future work must aim to tease apart the cognitive context under which we examine functional brain development in young children and take considerations into account unique to each age., Competing Interests: Declaration of competing interest None., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Individual differences in temperament have been theorized to be supported by differential recruitment of key neural regions, resulting in the distinct patterns of behavior observed throughout life. Although a compelling model, its rigorous and systematic testing is lacking, particularly within the heightened neuroplasticity of early childhood. The current study tested a model of the link between temperament, the brain, and behavior for cognitive flexibility in a sample of 4-5-year-old children (N = 123) using functional near-infrared spectroscopy (fNIRS) to assess prefrontal cortex (PFC) activation. Structural Equation Modeling (SEM) was used to explore the link between survey reports of temperamental effortful control, and both performance-based and neuroimaging measures of cognitive flexibility. Results indicated that greater parent-reported temperamental effortful control was associated with better performance on a cognitive flexibility task, and less activation of the DLPFC in preschoolers. These findings support the theorized model of the interrelatedness between temperamental tendencies, behavior, and brain activation and suggest that better temperamentally regulated children use the DLPFC more efficiently for cognitive flexibility., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)