Magnetic resonance imaging does not reveal structural alterations in the brain of grapheme-color synesthetes

Several publications have reported structural changes in the brain of synesthetes compared to controls, either local differences or differences in connectivity. In the present study, we pursued this quest for structural brain differences that might support the subjective experience of synesthesia. In particular, for the first time in this field, we investigated brain folding in comparing 45 sulcal shapes in each hemisphere of control and grapheme-color synesthete populations. To overcome flaws relative to data interpretation based only on p-values, common in the synesthesia literature, we report confidence intervals of effect sizes. Moreover, our statistical maps are displayed without introducing the classical, but misleading, p-value level threshold. We adopt such a methodological procedure to facilitate appropriate data interpretation and promote the “New Statistics” approach. Based on structural or diffusion magnetic resonance imaging data, we did not find any strong cerebral anomaly, in sulci, tissue volume, tissue density or fiber organization that could support synesthetic color experience. Finally, by sharing our complete datasets, we strongly support the multi-center construction of a sufficient large dataset repository for detecting, if any, subtle brain differences that may help understanding how a subjective experience, such as synesthesia, is mentally constructed.已有多项研究报道，联觉者（synesthetes）的大脑结构与对照组（controls）存在差异，既包括局部结构差异，也涵盖脑连接模式差异。本研究延续这一研究脉络，旨在探寻可能支撑联觉主观体验的大脑结构差异。尤为重要的是，本领域内首次针对大脑皮层折叠模式展开研究，对比了对照组与字形-颜色联觉者（grapheme-color synesthetes）群体两侧大脑半球（hemisphere）共45种脑沟形态（sulcal shapes）的特征。为规避联觉研究领域中常见的仅依赖p值（p-value）进行数据解读的固有缺陷，本研究同时报告了效应量（effect sizes）的置信区间（confidence intervals）。此外，我们在展示统计图谱（statistical maps）时未引入经典却易引发误导的p值阈值。我们采用该实验范式以保障数据解读的严谨性，并推广"New Statistics"研究思路。基于结构磁共振成像（structural magnetic resonance imaging）与弥散磁共振成像（diffusion magnetic resonance imaging）数据，本研究未发现能够支撑联觉色彩体验的显著脑异常，涉及脑沟形态、组织体积、组织密度或纤维组织结构等多个维度。最后，通过公开完整的数据集，我们倡议多中心共建大规模数据集资源库，以期在存在此类差异的情况下精准识别细微脑结构差异，进而助力揭示联觉这类主观体验的心理建构机制。