SPATIAL DISSIMILARITY TRAJECTORIES REVEAL RAPID FUNCTIONAL NETWORK REFINEMENT DURING EARLY INFANCY

The first six months of life mark a critical window for human brain development, characterized by rapid synaptic formation, axonal growth, and network reorganization. During this period, large-scale functional networks progressively mature. Although prior infant fMRI studies have characterized temporal functional connectivity, the spatial organization and refinement of brain networks during early infancy remain underexplored. In this study, we analyzed longitudinal resting-state fMRI from 74 typically developing infants (0–6 months; 137 scans) using group independent component analysis (ICA) with group-information-guided ICA (GIG-ICA) back-reconstruction. Spatial dissimilarity between each infant’s spatial map and the group-level map was quantified using cosine dissimilarity and Euclidean distance. Generalized additive models were applied to model age-related trends. Both cosine and Euclidean dissimilarity metrics showed significant decreases with age, indicating a progressive convergence of individual network topographies toward the group-level architecture. These findings reveal increasing spatial coherence and refinement of large-scale brain networks during early infancy, suggesting that spatial maturation complements the well-established functional integration observed in temporal connectivity studies.