Aix Marseille Univ, CNRS, ISM, Marseille, France.
Aix Marseille Univ, INSERM, INS, Inst Neurosci Syst, Marseille, France.
eNeuro. 2021 Jul 26;8(4). doi: 10.1523/ENEURO.0190-20.2021. Print 2021 Jul-Aug.
Generalization of sensorimotor adaptation across limbs, known as interlimb transfer, is a well-demonstrated phenomenon in humans, yet the underlying neural mechanisms remain unclear. Theoretical models suggest that interlimb transfer is mediated by interhemispheric transfer of information via the corpus callosum. We thus hypothesized that lesions of the corpus callosum, especially to its midbody connecting motor, supplementary motor, and premotor areas of the two cerebral hemispheres, would impair interlimb transfer of sensorimotor adaptation. To test this hypothesis, we recruited three patients: two rare stroke patients with recent, extensive callosal lesions including the midbody and one patient with complete agenesis. A prismatic adaptation paradigm involving unconstrained arm reaching movements was designed to assess interlimb transfer from the prism-exposed dominant arm (DA) to the unexposed non-dominant arm (NDA) for each participant. Baseline results showed that spatial performance of each patient did not significantly differ from controls, for both limbs. Further, each patient adapted to the prismatic perturbation, with no significant difference in error reduction compared with controls. Crucially, interlimb transfer was found in each patient. The absolute magnitude of each patient's transfer did not significantly differ from controls. These findings show that sensorimotor adaptation can transfer across limbs despite extensive lesions or complete absence of the corpus callosum. Therefore, callosal pathways connecting homologous motor, premotor, and supplementary motor areas are not necessary for interlimb transfer of prismatic reach adaptation. Such interlimb transfer could be mediated by transcallosal splenium pathways (connecting parietal, temporal and visual areas), ipsilateral cortico-spinal pathways or subcortical structures such as the cerebellum.
肢体间感觉运动适应的泛化，即肢体间转移，在人类中是一种经过充分证明的现象，但潜在的神经机制仍不清楚。理论模型表明，肢体间转移是通过胼胝体进行的大脑两半球间的信息传递介导的。因此，我们假设胼胝体，特别是其中连接两个大脑半球的运动、补充运动和运动前区的中体的损伤，会损害感觉运动适应的肢体间转移。为了验证这一假设，我们招募了三名患者：两名罕见的中风患者，近期胼胝体广泛受损，包括中体，以及一名完全无脑胼胝体的患者。设计了一个涉及无约束手臂伸展运动的棱镜适应范式，以评估每个参与者的来自暴露于棱镜的优势臂（DA）到未暴露的非优势臂（NDA）的肢体间转移。基线结果表明，每位患者的空间表现与对照组相比没有显著差异，无论是哪条手臂。此外，每位患者都适应了棱镜的干扰，与对照组相比，错误减少没有显著差异。至关重要的是，在每位患者中都发现了肢体间转移。每位患者的转移的绝对幅度与对照组没有显著差异。这些发现表明，尽管胼胝体存在广泛的损伤或完全缺失，感觉运动适应仍可以在肢体间转移。因此，连接同源运动、运动前和补充运动区的胼胝体通路对于棱镜手臂伸展适应的肢体间转移不是必需的。这种肢体间转移可能通过胼胝体压部通路（连接顶叶、颞叶和视觉区）、同侧皮质脊髓通路或小脑等皮质下结构介导。
