Age attenuates noise and increases symmetry of head movements during sleep resting-state fMRI in healthy neonates, infants, and toddlers.

Newborns produce spontaneous movements during sleep that are functionally important for their future development. This nuance has been previously studied using animal models and more recently using movement data from sleep resting-state fMRI (rs-fMRI) scans. Age-related trajectory of statistical features of spontaneous movements of the head is under-examined. This study quantitatively mapped a developmental trajectory of spontaneous head movements during an rs-fMRI scan acquired during natural sleep in 91 datasets from healthy children from ∼birth to 3 years old, using the Open Science Infancy Research upcycling protocol. The youngest participants studied, 2-3 week-old neonates, showed increased noise-to-signal levels as well as lower symmetry features of their movements; noise-to-signal levels were attenuated and symmetry was increased in the older infants and toddlers (all Spearman's rank-order correlations, P < 0.05). Thus, statistical features of spontaneous head movements become more symmetrical and less noisy from birth to ∼3 years in children. Because spontaneous movements during sleep in early life may trigger new neuronal activity in the cortex, the key outstanding question for in vivo, non-invasive neuroimaging studies in young children is not "How can we correct head movement better?" but rather: How can we represent all important sources of neuronal activity that shape functional connections in the still-developing human central nervous system?