New research from the University of Surrey has found that infants’ activity during sleep is rhythmic. The findings provide important insight into infant sleep cycles during the first year of life.
In the largest study of its kind, Surrey scientists led by Dr Eva Winnebeck looked at the development of sleep cycles in 152 infants aged 3, 6 and 12 months.
To learn more, the infants’ motor levels were closely monitored for 10 days at each age using an actigraphy device, a non-invasive wearable technology placed on the infant’s ankle. Parents were also provided with a wrist actigraphy device to measure movement during sleep.
During the first year of life, sleep undergoes remarkable development. Much to the relief of parents, infants’ sleep consisted of multiple short sleep cycles roughly evenly spaced over a 24-hour day, gradually transitioning into the night and consolidating into longer sleep periods.
Despite its importance to neurological and physical development, infant sleep is understudied in science. To learn more, we’re going back to basics and examining how infants move during sleep. This was the basis of sleep research before the discovery of REM and NREM sleep, and provides a useful means of examining infant sleep outside of the sleep laboratory. The more we learn, the more we can identify healthy sleep from unhealthy sleep, allowing parents and doctors to spot problems early and support optimal infant development. ”
Dr Eva Winnebeck, Lecturer in Chronobiology, University of Surrey
Scientists used a combination of signal processing techniques and analysis of more than 35,000 hours of infant sleep data to identify the existence of rhythmic patterns of inactivity in infants from the age of three months. Cycles of inactivity typically lasted 60 minutes and increased in 10 minute increments up to 12 months. Not surprisingly, infants had shorter cycles than their parents, whose cycles of inactivity lasted an average of 81 minutes. These findings are consistent with smaller studies examining REM and NREM sleep cycles, which confirm that sleep cycles gradually lengthen with development.
Limb inactivity was also found to be high at sleep onset and decrease over time, again reflecting REM and NREM dynamics.
Scientists also found that infants who were still breastfed at 12 months of age had longer cycles of inactivity than infants who were not breastfed. It was also found that mothers who were still breastfeeding their infants at this age had approximately 6.7 minutes longer menstrual cycles.
Scientists hypothesize that breastfeeding, due to its hormonal content (increased cortisol during the day and increased melatonin at night), could potentially cause circadian entrainment in infants and contribute to the maturation of the circadian system. However, further research is needed in this area.
Dr Gregory Hamad, visiting researcher at the University of Surrey and lead author of the study, said:
“When infants are asleep, they are less likely to move their bodies, so it is clear that inactivity levels correlate with sleep onset. However, what we found is that limb inactivity itself is rhythmic during sleep, with periodic alternations of non-REM and REM sleep during the night. The cycle of inactivity lengthens as the child ages and is a good indicator of what kind of sleep cycle an infant is in. Our findings help to advance our understanding of the complex relationship between sleep and development. ”
This research was published in the journal SLEEP.
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Reference magazines:
Hamad, G. others. (2026) Graphing infant sleep cycle development using actigraphy: Longitudinal evidence of extended ultradian cycles within the first year of life from 35,000 hours of sleep; sleep. DOI: 10.1093/sleep/zsag161. https://academic.oup.com/sleep/advance-article/doi/10.1093/sleep/zsag161/8707366
