A longitudinal study of infant sleep and its effects on cognitive development

Sleep is a common behaviour in all animals and crucial for physiological, social, emotional, and cognitive functioning. Previous studies have demonstrated the importance of sleep for cognition in adults, in particular with respect to attention and memory (Maquet, 2001; Diekelmann & Born, 2010). However, the role of sleep in developing infants has hitherto been relatively neglected. For instance, we do not know exactly whether and how sleep impacts on cognitive functioning nor which aspects of sleep matter more than others during this decisive period of life. We designed a cross-sectional and longitudinal study in order to explore these questions. Forty infants were followed longitudinally, measuring their sleep patterns with actigraphy for a week at months 4, 6, 8, and 10. Additionally, parents filled in a sleep diary and monthly questionnaires on sleep, cognitive, social, and motor development, as well as infant and parent sleep problems. Furthermore, three cognitive tasks using eye-tracking were conducted at each age. Sleep patterns changed most between 4 and 6 months: older infants had longer and less fragmented sleep duration. Regarding the eye-tracking tasks, we found a non-linear response over developmental time on the short-term memory task as well as an amelioration in number processing and shorter disengagement latencies. Habitual sleep was found to relate to short-term memory performance and number processing but not to reaction time or disengagement of attention. The association of sleep to cognition was stronger with respect to sleep fragmentation than to sleep duration. In general, infants with less time awake during the night performed better on the eye-tracking tasks. The discussion proposes explanations for what drives the differential associations of cognition with sleep duration/fragmentation and examines how the limitations of this work can inform future studies