Objective: Intraindividual variability in response time (RT) provides information about attention abilities beyond accuracy and mean RT. It could be an endophenotype for a wide range of clinical disorders and a general marker of neurological health or maladaptation. The default mode network (DMN) and the central executive and the salience networks (CEN ϩ SN) support response stability in adults. The aim of this study was to explore the associations of resting-state connectivity of the DMN and the CEN ϩ SN with lapses of attention in typically developing primary schoolchildren. Method: RT variability was measured by RT standard deviation in the self-paced Stroop-like Animal Size Test in 137 children aged 6 -11 years. Electrophysiological signatures of the DMN and the CEN ϩ SN were obtained using a seed-based oscillatory power envelope correlation in conjunction with beamformer spatial filtering. Results: Statistical nonparametric mapping showed that RT variability was positively associated with connectivity between the DMN and the posterior insula and the right temporal cortex (P FWE-corr Ͻ .006), suggesting that a greater focus of self-reflective internal attention may be associated with obstructed transition to an active processing mode. RT variability was negatively associated with connectivity between the DMN and the anterior cingulate and the anterior insula (P FWE-corr ϭ .001) overlapping with the SN, which handles top-down cognitive regulation. These associations were specifically found for the anterior DMN seed in the medial prefrontal cortex, which is involved in emotion and motivational circuits. Conclusions: Default network connectivity supporting RT variability may be involved in the development of internalizing and externalizing problems in childhood. Key PointsQuestion: Does the organization of brain networks at rest support behavioral stability in typically developing primary schoolchildren? Testing via electrophysiological signatures of networks. Findings: Greater response time variability was associated with stronger default mode network connectivity with surrounding structures and weakening of cooperation between the default mode network This article was published Online First September 14, 2020.

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Intraindividual response time variability (RTV) is considered as a general marker of neurological health. In adults, the central executive and salience networks (taskpositive networks, TPN) and the default mode network (DMN) are critical for RTV.Given that RTV decreases with growing up, and that boys are likely somewhat behind girls with respect to the network development, we aimed to clarify age and sex effects.Electroencephalogram was recorded during Stroop-like test performance in 124 typically developing children aged 5-12 years. Network fluctuations were calculated as changes of current source density (CSD) in regions of interest (ROIs) from pretest to 1-s test interval. In boys, TPN activation (CSD increase in ROIs included in the TPN) was associated with lower RTV, suggesting a greater engagement of attentional control.In children younger than 9.5 years, higher response stability was associated with the predominance of TPN activation over DMN activation (CSD increase in ROIs included in the TPN > that in the DMN); this predominance increased with age, suggesting that variability among younger children may be due to network immaturity. These findings suggest that the TPN and DMN may play different roles within the network mechanisms of RTV in boys and girls and at different developmental stages.