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The human cerebral cortex contains groups of areas that support sensory, motor, cognitive, and affective functions, often categorized into functional networks. These networks show stronger internal and weaker external functional connectivity (FC), with FC profiles more similar within the same network. Previous studies have shown these networks develop from nascent forms before birth to their mature, adult-like structures in childhood. However, these analyses often rely on adult functional network definitions. This study assesses the potential misidentification of infant functional networks when using adult models and explores the consequences and possible solutions to this problem. Our findings suggest that although adult networks only marginally describe infant FC organization better than chance, misidentification is primarily driven by specific areas. Restricting functional networks to areas with adult-like network clustering revealed consistent within-network FC across scans and throughout development. These areas are also near locations with low network identity variability. Our results highlight the implications of using adult networks for infants and offer guidance for selecting and utilizing functional network models based on research questions and scenarios.

The cerebral cortex consists of distinct areas that develop through intrinsic embryonic patterning and postnatal experiences. Accurate parcellation of these areas in neuroimaging studies improves statistical power and cross-study comparability. Given significant brain changes in volume, microstructure, and connectivity during early life, we hypothesized that cortical areas in 1- to 3-year-olds would differ markedly from neonates and increasingly resemble adult patterns as development progresses. Here, we parcellated the cerebral cortex into putative areas using local functional connectivity gradients in 92 toddlers at 2 years old. We demonstrate high reproducibility of these cortical regions across 1- to 3-year-olds in two independent datasets. The area boundaries in 1- to 3-year-olds were more similar to those in adults than those in neonates. While the age-specific group area parcellation better fit the underlying functional connectivity in individuals during the first 3 years, adult area parcellations might still have some utility in developmental studies, especially in children older than 6 years. Additionally, we provide connectivity-based community assignments of the parcels, showing fragmented anterior and posterior components based on the strongest connectivity, yet alignment with adult systems when weaker connectivity was included.

Background: While autism spectrum disorder (ASD) is defined by deficits in social communication with restricted interests and repetitive behaviors, autistic individuals often show early impairments in motor imitation that persist through childhood and into adulthood. High-density diffuse optical tomography (HD-DOT) overcomes logistical challenges of functional magnetic resonance imaging (fMRI) to provide an open scanning environment conducive to neuroimaging during naturalistic motor imitation. Additionally, the mirror neuron system (MNS) is crucial for understanding and imitating actions, and its dysfunction is hypothesized to underlie key ASD features. Objective: We aim to investigate brain function underlying motor observation and motor imitation in adult autistic and non-autistic individuals (NAI). We hypothesize that HD-DOT will reveal greater MNS activity during motor imitation than motor observation, and that MNS activity will exhibit a negative correlation with autistic traits. Methods: We imaged brain function using HD-DOT in N=100 participants as they passively observed videos of an actor completing sequences of meaningless arm movements. Additionally, while being simultaneously recorded with both HD-DOT and Kinect 3D cameras for computer-vision-based assessment of motor imitation (CAMI), participants imitated different videos of an actor completing similar arm movements. Responses to the tasks were estimated using general linear models, and multiple regression was used to investigate brain-behavior associations with autistic traits, using the Social Responsiveness Scale, and imitation fidelity as measured with CAMI. Results: Both motor observation and imitation tasks elicited significant activations in visual, temporal, and MNS areas, with imitation showing stronger activation in motor regions. Notably, MNS regions exhibited greater activation during observation than imitation. Additionally, activity during observation in the right parietal lobe correlated with autistic traits assessed with the SRS. Conclusions: Our findings provide robust evidence of shared and task-specific neural mechanisms underlying motor observation and imitation, emphasizing the differential engagement of MNS regions during motor observation and imitation.Competing Interest StatementThe authors have declared no competing interest.

The cerebral cortex comprises discrete cortical areas that form during development. Accurate area parcellation in neuroimaging studies enhances statistical power and comparability across studies. The formation of cortical areas is influenced by intrinsic embryonic patterning as well as extrinsic inputs, particularly through postnatal exposure. Given the substantial changes in brain volume, microstructure, and functional connectivity during the first years of life, we hypothesized that cortical areas in 1-to-3-year-olds would exhibit major differences from those in neonates and progressively resemble adults as development progresses. Here, we parcellated the cerebral cortex into putative areas using local functional connectivity gradients in 92 toddlers at 2 years old. We demonstrated high reproducibility of these cortical regions across 1-to-3-year-olds in two independent datasets. The area boundaries in 1-to-3-year-olds were more similar to adults than neonates. While the age-specific group parcellation fitted better to the underlying functional connectivity in individuals during the first 3 years, adult area parcellations might still have some utility in developmental studies, especially in children older than 6 years. Additionally, we provided connectivity-based community assignments of the parcels, showing fragmented anterior and posterior components based on the strongest connectivity, yet alignment with adult systems when weaker connectivity was included.