Humans are able to interact with objects with extreme flexibility. To achieve this ability, the brain does not only control specific muscular patterns, but it also needs to represent the abstract goal of an action, irrespective of its implementation. It is debated, however, how abstract action goals are implemented in the brain. To address this question, we used multivariate pattern analysis of functional magnetic resonance imaging data. Human participants performed grasping actions (precision grip, whole hand grip) with two different wrist orientations (canonical, rotated), using either the left or right hand. This design permitted to investigate a hierarchical organization consisting of three levels of abstraction: 1) "concrete action" encoding; 2) "effector-dependent goal" encoding (invariant to wrist orientation); and 3) "effector-independent goal" encoding (invariant to effector and wrist orientation). We found that motor cortices hosted joint encoding of concrete actions and of effector-dependent goals, while the parietal lobe housed a convergence of all three representations, comprising action goals within and across effectors. The left lateral occipito-temporal cortex showed effector-independent goal encoding, but no convergence across the three levels of representation. Our results support a hierarchical organization of action encoding, shedding light on the neural substrates supporting the extraordinary flexibility of human hand behavior.

中文翻译：

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人脑内的分层动作编码。

人类能够以极大的灵活性与物体进行交互。为了实现这种能力，大脑不仅控制特定的肌肉模式，而且还需要代表一个动作的抽象目标，而不管它的执行情况。然而，抽象的行动目标是如何在大脑中实现的，这一点存在争议。为了解决这个问题，我们使用了功能磁共振成像数据的多变量模式分析。人类参与者使用左手或右手以两种不同的手腕方向（规范的、旋转的）执行抓握动作（精确抓握、全手抓握）。这种设计允许研究由三个抽象级别组成的分层组织：1）“具体动作”编码；2）“效应器相关目标”编码（手腕方向不变）；和 3）“效应器独立目标”编码（效应器和手腕方向不变）。我们发现运动皮层承载了具体动作和效应器依赖目标的联合编码，而顶叶则容纳了所有三种表示的融合，包括效应器内和效应器之间的动作目标。左侧枕颞皮层显示出独立于效应器的目标编码，但在三个表示级别上没有收敛。我们的结果支持动作编码的分层组织，揭示了支持人类手部行为非凡灵活性的神经基质。而顶叶则容纳了所有三种表示的融合，包括效应器内部和效应器之间的行动目标。左侧枕颞皮层显示出独立于效应器的目标编码，但在三个表示级别上没有收敛。我们的结果支持动作编码的分层组织，揭示了支持人类手部行为非凡灵活性的神经基质。而顶叶则容纳了所有三种表示的融合，包括效应器内部和效应器之间的行动目标。左侧枕颞皮层显示出独立于效应器的目标编码，但在三个表示级别上没有收敛。我们的结果支持动作编码的分层组织，揭示了支持人类手部行为非凡灵活性的神经基质。