An alien limb is a debilitating disorder of volitional control. The core feature of alien limb is the performance of simple or complex semi-purposeful movements which the patient reports to be unintentional or unwanted, or occasionally in opposition to their intentions. Theories of the mechanism of alien limb phenomena have emphasised the role of disinhibition in the brain, and exaggerated action 'affordances'. However, despite advances in cognitive neuroscience research and a large public and media interest, there has been no unifying computational and anatomical account of the cause of alien limb movements. Here, we extend Bayesian brain principles to propose that alien limb is a disorder of 'predictive processing' in hierarchical sensorimotor brain networks. Specifically, we suggest that alien limb results from predictions about action outcomes that are afforded unduly high precision. The principal mechanism for this abnormally high precision is an impairment in the relay of input from medial regions, predominantly the supplementary motor area (SMA), which modulate the precision of lateral brain regions encoding the predicted action outcomes. We discuss potential implications of this model for future research and treatment of alien limb.

中文翻译：

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外来肢体综合症：对不想要的行为的贝叶斯描述。

异形肢体是一种意志控制的衰弱障碍。异形肢体的核心特征是表现出简单或复杂的半目的性运动，患者报告这些运动是无意的或不希望的，或者偶尔与他们的意图相反。外来肢体现象的机制理论强调了去抑制在大脑中的作用，并夸大了动作“可供性”。然而，尽管认知神经科学研究取得了进展，公众和媒体也对此产生了浓厚的兴趣，但对于外星肢体运动的原因，还没有统一的计算和解剖学解释。在这里，我们扩展了贝叶斯大脑原理，提出外来肢体是分层感觉运动大脑网络中的“预测处理”障碍。具体来说，我们建议外来肢体来自对动作结果的预测，这些预测被提供了过高的精度。这种异常高精度的主要机制是对来自内侧区域（主要是辅助运动区（SMA））的输入中继的损害，它调节编码预测动作结果的侧脑区域的精度。我们讨论了该模型对未来外来肢体研究和治疗的潜在影响。