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Large scale neuronal networks integrating several cortical areas mediate the complex functions of the brain such as sensorimotor integration. Little is known about the functional development of these networks and the maturational processes by which distant networks become functionally connected. We addressed this question in the postnatal rat sensorimotor system. Using epicranial multielectrode grids that span most of the cortical surface and intracortical electrodes we show that sensory evoked cortical responses continuously maturate throughout the first 3 weeks with the strongest developmental changes occurring in a very short time around postnatal day 13 (P13). Before P13 whisker stimulation evokes slow initially surface negative activity restricted mostly to the lateral parietal area of the contralateral hemisphere. In a narrow time window of approximately 48 h around P13 a new early sharp surface positive component emerges that coincides with subsequent propagation of activity to sensory and motor areas of both hemispheres. Our data show that this new component developing at the end of the second week corresponds principally to functional maturation of the supragranular cortical layers and appears to be crucial for the functional associations in the large scale sensorimotor cortical network. It goes along with the onset of whisking behavior as well as major synaptic and functional changes within the S1 cortex that are known to develop during this period.

Sleep-wake patterns and the electroencephalogram (EEG) during sleep undergo fundamental changes during adolescence. Scientific evidence indicates that these changes represent components of an extensive maturational brain remodeling process. Sleep during periods of brain maturation appears to be particularly important for health and behavior. Adolescents' sleep problems affect their cognitive and psychobehavioral functioning, making insufficient sleep during this developmental stage a significant international health concern. In this review, we summarize some key data concerning developmental changes in sleep behavior and regulation, and the association between sleep EEG changes and brain maturation. This review extends our understanding of adolescent sleep and highlights its significance for healthy development. We discuss the possibility to follow brain maturation and to detect errors in this maturational process by monitoring the developmental sleep EEG changes.