Despite a vast literature examining semantic impairment in Alzheimer's disease (AD), consensus regarding the nature of the deficit remains elusive. We re-considered this issue in the context of a framework that assumes semantic cognition can break down in two ways: (1) core semantic representations can degrade or (2) cognitive control mechanisms can become impaired [1]. We hypothesised and confirmed that the nature of semantic impairment in AD changes with disease severity. Patients at mild or severe stages of the disorder exhibited impairment across various semantic tasks but the nature of those deficits differed qualitatively for the two groups. Commensurate with early dysfunction of the cognitive control, temporoparietal-frontal-cingulate network, characteristics of deregulated semantic cognition were exhibited by the mild AD cases. In contrast, the severe AD group reproduced features of additional degradation of core semantic representations. These results suggest that spread of pathology into lateral anterior temporal lobes in later stage AD produces degradation of semantic representations, exacerbating the already deregulated system. Moreover, the dual nature of severe patients’ impairment was highlighted by disproportionately poor performance on tasks placing high demand on both conceptual knowledge and control processes–e.g., category fluency.

中文翻译：

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解开阿尔茨海默病的语义障碍：随着疾病严重程度的质变。

尽管有大量文献研究阿尔茨海默病 (AD) 的语义障碍，但关于缺陷性质的共识仍然难以达成。我们在一个框架的背景下重新考虑了这个问题，该框架假设语义认知可以通过两种方式分解：（1）核心语义表示可能会降级或（2）认知控制机制可能会受到损害 [1]。我们假设并证实 AD 中语义障碍的性质随疾病严重程度而变化。处于轻度或重度障碍阶段的患者在各种语义任务中表现出障碍，但两组的这些缺陷的性质在性质上有所不同。与早期认知控制、颞顶-额-扣带回网络功能障碍相称，轻度 AD 病例表现出语义认知失调的特征。相比之下，严重的 AD 组再现了核心语义表示额外退化的特征。这些结果表明，在 AD 后期，病理扩散到外侧前颞叶会导致语义表征的退化，从而加剧已经放松管制的系统。此外，严重患者损伤的双重性质因在对概念知识和控制过程（例如类别流畅性）提出高要求的任务中表现不佳而突出。