Mirroring emotional faces: Functional connectivity of the Mirror Neuron System in young children and adults

Abstract The Mirror Neuron System (MNS) underlies important neurocognitive functions, such as imitation learning, social cognition and empathy, and may facilitate the recognition of emotional expressions via motor simulation. However, its development remains poorly understood. This study investigated functional connectivity maturation of MNS-related areas between early childhood and adulthood during an emotional faces task. Using the innovative magnetoencephalography approach of optically pumped magnetometers (OPMs), we assessed whole-brain connectivity with 8 bilateral regions of interest (ROIs), representing the MNS, in 57 typically developing children aged 3-to-5 years and 27 adults. We applied both classical network-based statistic (NBS) and its more recent approach incorporating machine learning, NBS-Predict. We observed networks of increased connectivity after face presentation in both adults and children in broadband, as well as in the alpha and beta bands; only adults recruited a theta band network. The networks included connections between MNS ROIs and key limbic, prefrontal, parietal and occipital areas. Notably, adults exhibited a network of increased connectivity in broadband and theta band, with a trend towards right-lateralisation compared to children. Results were validated with NBS-Predict, with a comparable subnetwork exhibiting predictive features for classification between children and adults. Our findings suggest that the network involving MNS ROIs during observation of facial expressions evolves between early childhood and adulthood, consistent with right-hemisphere specialisation in emotional processing.