Age-related patterns in local spontaneous activity measured by fNIRS: greater unpredictability in infancy, local reorganization in childhood

The maturation of the brain is typically described at the whole-brain scale, whereas age-related changes in spontaneous activity within local brain regions have received comparatively little attention. Resting-state regional dynamics (RSRD) are defined as the temporal variability characteristics of activity within a single brain region under the resting state, and can stably reflect the intrinsic properties of spontaneous brain activity. The present study compared two age periods: infants (1-8 months of age) recorded during natural sleep and children (4-15 years of age) recorded during wakeful rest, corresponding to distinct developmental stages of rapid postnatal structural and functional brain development. The results suggested markedly different age-related feature patterns between the two groups: during infancy the predominant change was an increase in unpredictability, with RSRD activity becoming increasingly complex, whereas during childhood the dominant feature was a systematic reorganization of local waveform patterns. Age-related RSRD changes in the prefrontal cortex suggested a linear trend in infancy and a mixed linear-nonlinear trend in childhood, with inter-regional differences in the magnitude of feature changes. Vascular maturation-related indices suggested an association with RSRD feature changes during infancy, but not during childhood, suggesting that vascular factors may play a relatively more prominent role in early developmental stages. External data and exploratory internal cross-validation provided preliminary support for the age-related nature of these features, although further validation in larger, independent cohorts is needed.