MySpace Lab, Department of Clinical Neurosciences, University Hospital of Lausanne, University of Lausanne, Lausanne, CH-1011, Switzerland
C'MoN, Cognition, Motion and Neuroscience Unit, Fondazione Istituto Italiano di Tecnologia, Genova, 16163, Italy.
J Neurosci. 2023 Mar 1;43(9):1572-1589. doi: 10.1523/JNEUROSCI.1976-21.2022. Epub 2023 Jan 30.
Despite the tight coupling between sensory and motor processing for fine manipulation in humans, it is not yet totally clear which specific properties of the fingers are mapped in the precentral and postcentral gyrus. We used fMRI to compare the morphology, connectivity, and encoding of the motor and tactile finger representations (FRs) in the precentral and postcentral gyrus of 25 5-fingered participants (8 females). Multivoxel pattern and structural and functional connectivity analyses demonstrated the existence of distinct motor and tactile FRs within both the precentral and postcentral gyrus, integrating finger-specific motor and tactile information. Using representational similarity analysis, we found that the motor and tactile FRs in the sensorimotor cortex were described by the perceived structure of the hand better than by the actual hand anatomy or other functional models (finger kinematics, muscles synergies). We then studied a polydactyly individual (i.e., with a congenital 6-fingered hand) showing superior manipulation abilities and divergent anatomic-functional hand properties. The perceived hand model was still the best model for tactile representations in the precentral and postcentral gyrus, while finger kinematics better described motor representations in the precentral gyrus. We suggest that, under normal conditions (i.e., in subjects with a standard hand anatomy), the sensorimotor representations of the 5 fingers in humans converge toward a model of perceived hand anatomy, deviating from the real hand structure, as the best synthesis between functional and structural features of the hand. Distinct motor and tactile finger representations exist in both the precentral and postcentral gyrus, supported by a finger-specific pattern of anatomic and functional connectivity across modalities. At the representational level, finger representations reflect the perceived structure of the hand, which might result from an adapting process harmonizing (i.e., uniformizing) the encoding of hand function and structure in the precentral and postcentral gyrus. The same analyses performed in an extremely rare polydactyly subject showed that the emergence of such representational geometry is also found in neuromechanical variants with different hand anatomy and function. However, the harmonization process across the precentral and postcentral gyrus might not be possible because of divergent functional-structural properties of the hand and associated superior manipulation abilities.
尽管人类在精细操作中感觉和运动处理之间紧密耦合，但手指的哪些特定属性映射到大脑中央前回和中央后回仍然不完全清楚。我们使用 fMRI 比较了 25 名 5 指参与者（8 名女性）的中央前回和中央后回中运动和触觉手指代表区（FR）的形态、连接和编码。多体素模式以及结构和功能连接分析表明，中央前回和中央后回中都存在明显的运动和触觉 FR，整合了手指特定的运动和触觉信息。使用代表性相似性分析，我们发现感觉运动皮层中的运动和触觉 FR 可以更好地由感知到手的结构来描述，而不是由实际手的解剖结构或其他功能模型（手指运动学、肌肉协同作用）来描述。然后，我们研究了一位多指个体（即，先天性 6 指手），该个体具有出色的操作能力和不同的解剖-功能手特征。感知到手的模型仍然是中央前回和中央后回中触觉代表的最佳模型，而手指运动学更好地描述了中央前回中的运动代表。我们认为，在正常情况下（即，在具有标准手解剖结构的受试者中），人类 5 个手指的感觉运动代表会向感知到手的解剖结构的模型收敛，偏离真实的手结构，因为这是手的功能和结构特征之间的最佳综合。在中央前回和中央后回中都存在明显的运动和触觉手指代表，这是由模态之间特定手指的解剖和功能连接模式支持的。在表示水平上，手指表示反映了到手的感知结构，这可能是由于协调（即统一）中央前回和中央后回中手功能和结构编码的适应过程的结果。在一位极其罕见的多指个体中进行的相同分析表明，这种表示几何形状的出现也存在于具有不同手解剖结构和功能的神经机械变体中。然而，由于手的功能结构特性的发散以及相关的出色操作能力，中央前回和中央后回之间的协调过程可能是不可能的。
