Department of Biological Sciences, University of Bergen, Postboks 7803, 5020 Bergen, Norway.
Department of Biological and Medical Psychology, University of Bergen, Postboks 7807, 5020 Bergen, Norway.
Cereb Cortex. 2023 Dec 9;33(24):11623-11633. doi: 10.1093/cercor/bhad396.
Brain asymmetry is a cornerstone in the development of higher-level cognition, but it is unclear whether and how it differs in males and females. Asymmetry has been investigated using the laterality index, which compares homologous regions as pairwise weighted differences between the left and the right hemisphere. However, if asymmetry differences between males and females are global instead of pairwise, involving proportions between multiple brain areas, novel methodological tools are needed to evaluate them. Here, we used the Amsterdam Open MRI collection to investigate sexual dimorphism in brain asymmetry by comparing laterality index with the distance index, which is a global measure of differences within and across hemispheres, and with the subtraction index, which compares pairwise raw values in the left and right hemisphere. Machine learning models, robustness tests, and group analyses of cortical volume, area, thickness, and mean curvature revealed that, of the three indices, distance index was the most successful biomarker of sexual dimorphism. These findings suggest that left-right asymmetry in males and females involves global coherence rather than pairwise contrasts. Further studies are needed to investigate the biological basis of local and global asymmetry based on growth patterns under genetic, hormonal, and environmental factors.
大脑不对称性是高级认知发展的基石，但目前尚不清楚男性和女性之间是否存在差异，以及差异的程度如何。人们使用侧性指数来研究不对称性，该指数通过比较左右半球之间的左、右半脑的成对加权差异来评估不对称性。然而，如果男性和女性之间的不对称性差异是全局性的，而不是成对的，涉及多个脑区之间的比例，则需要新的方法学工具来评估这些差异。在这里，我们使用阿姆斯特丹开放 MRI 集合，通过比较侧性指数与距离指数（一种评估左右半球内和跨半球差异的全局指标）和减法指数（比较左右半球的原始值的成对差异）来研究大脑不对称性的性别二态性。机器学习模型、稳健性测试以及皮质体积、面积、厚度和平均曲率的组分析表明，在这三个指数中，距离指数是性别二态性的最佳生物标志物。这些发现表明，男性和女性的左右不对称性涉及全局一致性，而不是成对对比。需要进一步的研究来探讨基于遗传、激素和环境因素下的生长模式的局部和全局不对称的生物学基础。
