Chelsea and Westminster NHS Foundation Trust, West Middlesex University Hospital, Isleworth, United Kingdom; Department of Brain Sciences, Faculty of Medicine, Imperial College, London, United Kingdom.
Division of Neuroscience, University Vita Salute San Raffaele and IRCCS San Raffaele, Milan, Italy.
Handb Clin Neurol. 2023;195:127-133. doi: 10.1016/B978-0-323-98818-6.00029-7.
The parietal lobe has been implicated in the sensorimotor control and integration that supports the skillful use of our hands to reach for, grasp, and manipulate objects in the environment. This area is involved in several circuits within the classic subdivisions of the dorsal stream. Recently, the dorsal stream has been further divided into a "dorso-dorsal" and a "ventro-dorsal" streams. The ventro-dorsal stream is regarded as functionally linked to object manipulation. The dorso-dorsal stream is proposed to subserve reaching and online control of actions. Affordances indicate action possibilities characterized by object properties the environment provides. Affordances are likely represented by the dorsal stream. They code structural object properties that can elicit actions. A further subdivision of affordances into "stable" and "variable" allows an understanding of the neuronal mechanisms underlying object manipulation. Whereas stable affordances emerge from slow processing of visual information based on knowledge of object properties from previous experiences and object interaction, variable affordances emerge from fast online processing of visual information during actual object interaction, within a changing environment. The relevance of the dorsal stream subdivisions in this context is that the dorso-dorsal stream is associated with coding of variable affordances, while that of the dorso-ventral stream is implicated in action representations elicited by stable affordances. A greater interaction between these and ventral stream perceptual and semantic representations allows the parietal control of hand movement. An understanding of these networks is likely to underlie recovery from complex deficits described in limb apraxias.
顶叶在感觉运动控制和整合中起作用，支持我们熟练地使用手去够、抓和操作环境中的物体。该区域涉及经典背流的几个回路。最近，背流进一步分为“背背流”和“腹背流”。腹背流被认为与物体操作功能相关。背背流被提议用于到达和在线控制动作。可供性表明了由环境提供的物体特性所具有的动作可能性。可供性可能由背流表示。它们编码可以引发动作的结构物体属性。可供性的进一步细分，分为“稳定”和“可变”，可以理解物体操作背后的神经元机制。稳定的可供性是从基于先前经验和物体相互作用中对物体属性的知识的视觉信息的缓慢处理中产生的，而可变的可供性是在实际的物体相互作用中从视觉信息的快速在线处理中产生的，在变化的环境中。在这种情况下，背流细分的相关性在于，背背流与可变可供性的编码有关，而背腹流则与稳定可供性引起的动作表示有关。这些与腹侧流感知和语义表示之间的更大交互作用允许顶叶对手部运动的控制。对这些网络的理解可能是理解肢体失用症中描述的复杂缺陷恢复的基础。
