Understanding Action Selection in the Tool Use Network

项目总结： 熟练地使用工具是人类认知的决定性成就，并通过存储特定于工具的动作记忆来实现。许多工具与多个操作相关联，并且大多数日常任务与多个工具相关联。肢体失用症是一种常见的、致残的、令人费解的左半球疾病，其特征是在激活和选择任务适当的工具动作方面存在明显的缺陷。对于在神经完好的大脑中进行这种选择的认知机制和大脑区域，或者这些过程在失用症中是如何出错的，人们知之甚少。在其他几个认知领域，有人提出，适当的反应选择是通过有偏见的竞争发生的--即，对相互竞争的传入信息进行优先排序，以实现适当的反应选择。利用这些框架的前景，我们开发了一个新的功能神经解剖学模型，该模型描述了特定左半球工具使用网络中的偏向竞争。该模型被称为“两个行动系统+”(2AS+)，产生了关于决定工具行动选择的主要原则及其在失用症中的缺陷的可检验的假设。具体地说，我们假设1)工具动作之间的竞争受到工具动作表征的分级相似性的影响，主要由左侧后颞叶(PTC)实现；2)竞争过程的结果受工具动作表征的激活强度和时间的影响，并取决于左侧PTC和顶叶的动态相互作用；3)结果进一步受到偏向于适合于目标和背景的工具动作的竞争机制的影响，如左额下回(IFG)及其与边缘上回(SMG)的联系，4)失用症有两种亚型，一种是前向亚型，表现为不能正确解决工具动作竞争，另一种是后方亚型，反映竞争减弱。这些假说将使用一些互补的方法在健康和有脑损伤的参与者中进行测试，包括基于体素的病变症状映射、静息功能连接、具有多体素模式分析的功能磁共振成像以及眼睛跟踪。通过明确视觉运动信息何时以及如何在工具表征中发挥作用，拟议的实验有望批判性地约束声称工具自动唤起他们的行动的“具体化”认知理论。这项研究还将通过在认知-神经解剖学模型中锚定相关结构来推进对工具动作的理论理解，阐明动作表征是如何组织和激活的，并提高我们对影响失用错误和再学习的机制的理解，这对康复具有启示意义。

Project Summary: Skilled use of tools is a defining achievement of human cognition, and is enabled by the storage of tool-specific action memories. Many tools are associated with more than one action, and most everyday tasks are associated with more than one tool. Limb apraxia is a common, disabling, and puzzling left-hemisphere disorder characterized by prominent deficits in activating and selecting task-appropriate tool actions. Little is known about the cognitive mechanisms and brain regions enabling such selection in the neurologically intact brain, or how these processes go awry in apraxia. In several other cognitive domains, it has been suggested that appropriate response selection occurs via biased competition—that is, the prioritization of competing incoming information to enable appropriate response selection. Capitalizing on the promise of such frameworks, we have developed a new functional-neuroanatomic model of biased competition in a specific left hemisphere Tool Use network. Called “Two Action Systems Plus” (2AS+), the model generates testable hypotheses about the major principles determining tool action selection, and their deficiencies in apraxia. Specifically, we hypothesize that 1) Competition between tool actions is influenced by the graded similarity of tool action representations, as implemented primarily by the left posterior temporal cortex (pTC), 2) The outcome of the competitive process is affected by the strength and timing of activation of tool action representations, and depends on the dynamic interplay of left pTC and the parietal lobes, 3) Outcome is further influenced by a mechanism that biases competition towards the tool action that is appropriate to goals and context, as implemented by the left inferior frontal gyrus (IFG) and its connections with the supramarginal gyrus (SMG), and 4) There are two subtypes of apraxia characterized by distinct failures in the competitive selection process: an anterior subtype characterized by inability to appropriately resolve tool action competition, and a posterior subtype reflecting weakened competition. These hypotheses will be tested using a number of complementary methods with healthy and brain-lesioned participants, including voxel-based lesion symptom mapping, resting functional connectivity, fMRI with multi-voxel pattern analyses, and eyetracking. By specifying when and how visuomotor information plays a role in tool representations, the proposed experiments promise to critically constrain “embodied” cognition theories claiming that tools automatically evoke their actions. The proposed research will also advance the theoretical understanding of tool action by anchoring relevant constructs in a cognitive-neuroanatomic model, clarify how action representations are organized and activated, and improve our understanding of the mechanisms affecting errors and re-learning in apraxia, with implications for rehabilitation.