Development of slow oscillation–spindle coupling from infancy to toddlerhood

Abstract

Sleep has been demonstrated to support memory formation from early life on. The precise temporal coupling of slow oscillations with spindles has been suggested as a mechanism facilitating this consolidation process in thalamocortical networks. Here, we investigated the development of sleep spindles and slow oscillations and their coordinate interplay comparing frontal, central and parietal electroencephalogram recordings during a nap between infants aged 2–3 months (n = 31) and toddlers aged 14–17 months (n = 49). Spindles and slow oscillations showed quite different maturational patterns between age groups, as to topography, amplitude, and density. Notably, spindle-slow oscillation co-occurrence in the infants did not exceed chance levels, and was increased to significant levels only in the toddlers. In the infants, the slow oscillation upstate over frontocortical regions was even associated with a significant decrease in spindles, contrasting with the adult-like increase in spindles seen in toddlers. These results point to an immature processing in thalamo-cortical networks during sleep in early infancy, possibly diminishing efficacy of sleep-dependent memory formation at this age.