Twitching in sleeping premature infants provides a sensitive behavioral assay of early motor control

Limb twitching is among the earliest observable behaviors in human development and a hallmark of active (REM) sleep. Systematic assessments in full-term infants have revealed functional features that informal observation cannot capture. Because preterm infants spend even more time asleep and are at heightened risk for neurodevelopmental disorders, we provide the first systematic characterization of twitching at 34-35 weeks postmenstrual age. Preterm infants exhibit an immense quantity of twitching across the body, underscoring its developmental significance. The spatiotemporal structure of twitching also changes with age, including a selective increase in finger and toe twitching. Unexpectedly, during periods of tracé alternant, a precursor to quiet sleep, twitching appears in brief bouts that are almost exclusively restricted to the legs. These findings show how this abundant but overlooked sleep behavior provides a sensitive assay of the developing neural control of movement, with implications for understanding typical and atypical development.