Emergence of mature cortical activity in wakefulness and sleep in healthy preterm and full-term infants

Study Objectives: Cortical activity patterns develop rapidly over the equivalent of the last trimester of gestation, in parallel with the establishment of sleep architecture. However, the emergence of mature cortical activity in wakefulness compared to sleep states in healthy pre-term infants is poorly understood. Methods: To investigate whether cortical activity has a different developmental profile in each sleep-wake state, we recorded 11-channels EEG, EOG and respiratory movement for one hour from 115 infants 34-43 weeks corrected age, with 0.5-17 days of postnatal age. We characterised the trajectory of delta, theta and alpha-beta oscillations in wakefulness, REM sleep and non-REM sleep by calculating the power spectrum of the EEG, averaged across artefact-free epochs. Results: Delta oscillations in wakefulness and REM sleep decrease with corrected age, particularly in the temporal region, but not in non-REM sleep. Theta oscillations increase with corrected age in sleep, especially non-REM sleep, but not in wakefulness. On the other hand, alpha-beta oscillations decrease predominantly with postnatal age, independently of sleep-wake state, particularly in the occipital region. Conclusions: The developmental trajectory of delta and theta rhythms is state-dependent and results in changed cortical activity patterns between states with corrected age, which suggests that these frequency bands may have particular functional roles in each state. Interestingly, postnatal age is associated with a decrease in alpha-beta oscillations overlying primary visual cortex in every sleep-wake state, suggesting that postnatal experience (including the first visual input through open eyes during periods of wakefulness) is associated with resting-state visual cortical activity changes