Institut des Neurosciences Cognitives, CNRS, 67 Blv Pinel, 69675 Bron, France.
Neuroimage. 2012 Jan 2;59(1):556-64. doi: 10.1016/j.neuroimage.2011.07.046. Epub 2011 Jul 23.
Animal and human studies have shown that the parietal and the ventral premotor cortices constitute the neural substrate of the so-called mirror system. The word "mirror" originally referred to the discovery of neurons in non-human primates whose visual response echoes their motor response. This account proposes that action understanding and imitation depend on a mechanism which activates directly our own motor system as we observe the actions of other agents (Rizzolatti and Sinigaglia, 2010). Single unit recording experiments have also demonstrated that parietal neurons have predictive activity and discharge well ahead of a planned movement. Interestingly, patients with parietal damage can show impairments in their ability to imitate or understand an observed action, but they have also difficulties in monitoring early phases of their own movement planning, be it simple reaching movements or more complex object-directed actions. The fact that both deficits may co-occur after a parietal lesion raises the question whether this reflects the impairment of a common mechanism. To address this question we examined EEG activity in patients with selective lesions in the inferior parietal lobe (N=6) who were requested to watch passively a video showing an actor grasping a colored object. The object's color cued the subject that the actor was about to move. We recorded the Readiness Potential (RP), a marker of motor preparation which also arises when preparing to observe an action (Kilner et al., 2004). Parietal patients' performance was compared to that of neurologically normal subjects (n=9) and patients with a ventral premotor cortex lesion (N=4). We show that neurologically normal subjects and premotor patients exhibit a significant RP prior to the observed action, whereas no such RP is observed in parietal patients. Our results indicate that parietal cortex injury alters the ability to monitor the early planning phases not only of one's own actions but those of other agents as well. We speculate that parietal activity during action observation does not only or essentially reflect a mirroring process, as recently proposed by mirror neurons' account, but involve instead an anticipatory process which arises through prior learning and predictive mechanisms.
动物和人类研究表明，顶叶和腹侧运动前皮质构成了所谓镜像系统的神经基础。“镜像”一词最初指的是在非人类灵长类动物中发现的神经元，其视觉反应与运动反应相呼应。这种说法提出，动作理解和模仿依赖于一种机制，即当我们观察其他主体的动作时，该机制会直接激活我们自己的运动系统（Rizzolatti 和 Sinigaglia，2010）。单细胞记录实验还表明，顶叶神经元具有预测性活动，并在计划运动之前提前放电。有趣的是，顶叶损伤的患者可能表现出模仿或理解观察到的动作的能力受损，但他们也难以监测自己运动计划的早期阶段，无论是简单的伸手动作还是更复杂的物体定向动作。顶叶损伤后这两种缺陷都可能同时出现，这就提出了一个问题，即这是否反映了一种共同机制的损伤。为了解决这个问题，我们检查了 6 名选择性顶叶下叶损伤患者的 EEG 活动，他们被要求被动观看一段显示演员抓握有色物体的视频。物体的颜色提示演员即将移动。我们记录了预备电位（RP），这是运动准备的一个标志物，当准备观察动作时也会产生（Kilner 等人，2004）。将顶叶患者的表现与神经正常的受试者（n=9）和腹侧运动前皮质损伤患者（n=4）进行比较。我们发现，神经正常的受试者和运动前皮质患者在观察到动作之前会出现显著的 RP，而顶叶患者则没有这种 RP。我们的结果表明，顶叶皮质损伤不仅改变了监测自身动作早期规划阶段的能力，也改变了监测其他主体动作早期规划阶段的能力。我们推测，在观察动作时，顶叶活动不仅不反映镜像神经元理论所提出的镜像过程，而且还涉及通过先前学习和预测机制产生的预期过程。
