Tracing infant sleep neurophysiology longitudinally from 3 to 6 months: EEG insights into brain development

Sleep is critical for brain plasticity during early development, yet individual maturation of sleep neurophysiology in infancy remains poorly characterized. Slow wave activity (SWA) is a key marker of cortical maturation and experience-dependent plasticity, making early regional sleep dynamics highly relevant for neurodevelopmental health. We conducted a longitudinal high-density EEG study in 11 healthy infants, of whom 9 contributed analyzable EEG data at both 3 and 6 months. We assessed non-rapid eye movement (NREM) sleep and analyzed the maturation of SWA (0.75-4.25 Hz), theta power (4.5-7.5 Hz), and sigma power (9.75-14.75 Hz) across scalp regions and their associations with behavioral development. From 3 to 6 months, SWA increased maximally in occipital regions, while theta power exhibited a global increase. Sigma power, initially concentrated centrally, dispersed towards frontal regions. Greater frontal power increases correlated with higher motor (theta) and personal-social skill scores (sigma) at 6 months. These findings establish a framework for typical infant sleep EEG maturation, highlighting frequency-specific and regionally distinct developmental patterns. This study provides the first longitudinal evidence that early changes in sleep EEG topography reflect individual developmental trajectories, supporting its utility as a non-invasive and yet precise biomarker for early identification of atypical neurodevelopment at preverbal ages.