The functional topography of the human primary somatosensory cortex hand area is a widely studied model system to understand sensory organization and plasticity. It is so far unclear whether the underlying 3D structural architecture also shows a topographic organization. We used 7 Tesla (7T) magnetic resonance imaging (MRI) data to quantify layer-specific myelin, iron, and mineralization in relation to population receptive field maps of individual finger representations in Brodman area 3b (BA 3b) of human S1 in female and male younger adults. This 3D description allowed us to identify a characteristic profile of layer-specific myelin and iron deposition in the BA 3b hand area, but revealed an absence of structural differences, an absence of low-myelin borders, and high similarity of 3D microstructure profiles between individual fingers. However, structural differences and borders were detected between the hand and face areas. We conclude that the 3D structural architecture of the human hand area is nontopographic, unlike in some monkey species, which suggests a high degree of flexibility for functional finger organization and a new perspective on human topographic plasticity.

SIGNIFICANCE STATEMENT Using ultra-high-field MRI, we provide the first comprehensive in vivo description of the 3D structural architecture of the human BA 3b hand area in relation to functional population receptive field maps. High similarity of precise finger-specific 3D profiles, together with an absence of structural differences and an absence of low-myelin borders between individual fingers, reveals the 3D structural architecture of the human hand area to be nontopographic. This suggests reduced structural limitations to cortical plasticity and reorganization and allows for shared representational features across fingers.

人类初级体感皮层手部区域的功能地形是一个被广泛研究的模型系统，用于了解感觉组织和可塑性。目前还不清楚底层的 3D 结构架构是否也显示了地形组织。我们使用 7 特斯拉 (7T) 磁共振成像 (MRI) 数据来量化与女性和人类 S1 的 Brodman 区域 3b (BA 3b) 中个体手指表征的群体感受野图相关的层特异性髓磷脂、铁和矿化情况。男性年轻人。这种 3D 描述使我们能够识别 BA 3b 手部区域的层特异性髓磷脂和铁沉积的特征轮廓，但揭示了个体之间不存在结构差异、不存在低髓磷脂边界以及 3D 微观结构轮廓的高度相似性。手指。然而，检测到手部和面部区域之间的结构差异和边界。我们得出的结论是，与某些猴子物种不同，人类手部区域的 3D 结构体系是非地形的，这表明功能性手指组织具有高度的灵活性，并为人类地形可塑性提供了新的视角。

意义声明使用超高场 MRI，我们首次对人类 BA 3b 手部区域与功能群体感受野图相关的 3D 结构体系进行了全面的体内描述。精确的手指特定 3D 轮廓的高度相似性，加上各个手指之间不存在结构差异和低髓磷脂边界，揭示了人类手部区域的 3D 结构体系是非地形的。这表明减少了皮质可塑性和重组的结构限制，并允许跨手指共享表征特征。