Background: Brain lateralization, the hemispheric specialization of functional networks, is essential for motor and cognitive functions. However, how intensive athletic training shapes hemispheric organization remains poorly understood. This study investigated the formation of functional lateralization in elite athletes through long-term intensive training and its potential alteration by external factors, specifically sport-related concussions. Methods: Resting-state functional magnetic resonance imaging data were collected from 13 world class gymnasts (WCGs) and 14 nonathletic controls. Longitudinal data were collected from 18 soccer players and eight golfers before and after one season, with concussions monitored in the soccer players. Laterality indices of hemispheric integration and segregation (LIint and LIseg) were calculated to quantify hemispheric differences in information processing for each brain region, and the standard laterality index (LI) was employed to measure hemispheric asymmetry. Associations between laterality indices and neurotransmitter receptor/transporter densities were examined. Postseason changes in these indices were assessed to evaluate the effects of concussion on brain lateralization. Results: The WCGs showed significantly increased LIint in several left-hemispheric regions, including the precentral gyrus, cingulate gyrus, thalamus, superior parietal lobule, and lateral occipital cortex compared with the healthy controls, although no significant differences were found in LIseg. Furthermore, the LI analysis revealed that the WCGs showed higher hemispheric asymmetry in the left precentral gyrus, cingulate gyrus, and thalamus. These laterality indices also were positively correlated with certain neurotransmitters. Similar patterns of enhanced lateralization and neurotransmitter associations were observed in soccer players and golfers. However, no significant changes in laterality indices were observed as a result of concussions sustained during the season. Conclusions: Long-term intensive training enhances functional integration in the left hemisphere, leading to stable brain lateralization patterns resilient to sport-related concussions.
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