From co-occurrence to increasingly precise temporal coordination: Development of slow oscillation-spindle coupling from infancy to toddlerhood

Abstract

The precise temporal coordination of sleep spindles and slow oscillations (SOs) is a key mechanism of memory consolidation during sleep, yet little is known about its emergence early in life. Here, we investigated the development of SO-spindle coupling in 9- to 16-month-old infants and toddlers. While morphologies of spindles and SOs were largely comparable between infants younger than one year and toddlers older than one year, their temporal coordination showed clear age-related changes. In infants, SO-spindle co-occurrence was highest over occipital cortex regions, as was to be expected by chance based on the spatial distribution of the two oscillations. Co-occurrence rates in infants already exceeded chance level, but only at central regions where the highest co-occurrence rates were observed in toddlers. Moreover, a nesting of spindles into the upstate of SOs was evident in fronto-central regions even in infants, and increased in strength and precision with age. Together, these findings suggest that coordinated SO-spindle coupling emerges in the second half of the first year of life and becomes increasingly precise across the transition into toddlerhood.