Most stroke victims experience motor deficits, usually referred to collectively as hemiparesis. While hemiparesis is one of the most common and clinically recognizable motor abnormalities, it remains under-characterized in terms of its behavioral subcomponents and their interactions. Hemiparesis is comprised of both negative and positive motor signs. Negative signs consist of weakness and loss of motor control (dexterity), whereas positive signs consist of spasticity, abnormal resting posture, and intrusive movement synergies (abnormal muscle co-activations during voluntary movement). How positive and negative signs interact, and whether a common mechanism generates them, remains poorly understood. Here we employed a planar, arm-supported reaching task to assess post-stroke arm dexterity loss, which we compared to the Fugl-Meyer stroke scale; a measure primarily reflecting abnormal synergies. We examined 53 patients with hemiparesis after a first-time ischemic stroke. Reaching kinematics were markedly more impaired in patients with subacute (<3 months) compared to chronic (>6 months) stroke even when matched for Fugl-Meyer score. This suggests a dissociation between abnormal synergies (reflected in the Fugl-Meyer scale) and loss of dexterity, which in turn suggests different underlying mechanisms. Moreover, dynamometry suggested that Fugl-Meyer scores capture weakness as well as abnormal synergies, in line with these two deficits sharing a neural substrate. These findings have two important implications: First, clinical studies that test for efficacy of rehabilitation interventions should specify which component of hemiparesis they are targeting and how they propose to measure it. Second, there may be an opportunity to design rehabilitation interventions to address specific subcomponents of hemiparesis.

中文翻译：

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重新审视中风的阳性和阴性体征：协同作用、虚弱和无法达到灵巧性之间的分离

大多数中风患者会出现运动障碍，通常统称为偏瘫。虽然偏瘫是最常见和临床上可识别的运动异常之一，但在其行为子成分及其相互作用方面仍然缺乏特征。偏瘫由阴性和阳性运动征象组成。阴性体征包括无力和失去运动控制（灵巧），而阳性体征包括痉挛、异常休息姿势和侵入性运动协同作用（随意运动期间异常的肌肉共同激活）。积极和消极的迹象如何相互作用，以及是否有共同的机制产生它们，仍然知之甚少。在这里，我们采用了一个平面的、手臂支撑的伸手任务来评估中风后手臂灵活性的损失，我们将其与 Fugl-Meyer 中风量表进行了比较；一项主要反映异常协同效应的措施。我们检查了 53 名首次缺血性卒中后偏瘫的患者。与慢性（> 6 个月）中风患者相比，即使与 Fugl-Meyer 评分相匹配，亚急性（<3 个月）患者的运动学受损程度也明显更高。这表明异常协同作用（反映在 Fugl-Meyer 量表中）与灵巧性丧失之间存在分离，这反过来又表明了不同的潜在机制。此外，测力法表明 Fugl-Meyer 分数捕捉弱点以及异常协同作用，与这两个共享神经基质的缺陷一致。这些发现有两个重要意义：第一，测试康复干预有效性的临床研究应明确他们针对的是偏瘫的哪个部分以及他们建议如何测量它。其次，可能有机会设计康复干预措施来解决偏瘫的特定子成分。