Department of Psychology, University of York, York, UK.
Cortex. 2013 Mar;49(3):611-25. doi: 10.1016/j.cortex.2012.10.008. Epub 2012 Nov 13.
Recent studies suggest that a complex, distributed neural network underpins semantic cognition. This article reviews our contribution to this emerging picture and traces the putative roles of each region within this network. Neuropsychological studies indicate that semantic cognition draws on at least two interacting components: semantic representations [degraded in semantic dementia (SD)] and control processes [deficient in patients with multimodal semantic impairment following stroke aphasia (SA)]. To explore the first component, we employed distortion-corrected functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) in healthy volunteers: these studies convergently indicated that the anterior temporal lobes (ATLs; atrophied in SD) combine information from different modalities within an amodal semantic "hub". Regions of cortex that code specific semantic features ("spokes") also make a critical contribution to knowledge within particular categories. This network of brain regions interacts with semantic control processes reliant on left inferior frontal gyrus (LIFG), posterior middle temporal gyrus (pMTG) and inferior parietal cortices. SA patients with damage to these regions have difficulty focussing on aspects of knowledge that are relevant to the current goal or context, in both verbal and non-verbal tasks. SA patients with LIFG and temporoparietal lesions show similar deficits of semantic control, suggesting that a large-scale distributed cortical network underpins semantic control. Convergent evidence is again provided by fMRI and TMS. We separately manipulated the representational and control demands of a semantic task in fMRI, and found a dissociation within the temporal lobe: ATL was sensitive to the number of meanings retrieved, while pMTG and LIFG showed effects of semantic selection. Moreover, TMS to LIFG and pMTG produced equal disruption of tasks tapping semantic control. The next challenges are to delineate the specific roles of each region within the semantic control network and to specify the way in which control processes interact with semantic representations to focus processing on relevant features of concepts.
最近的研究表明，语义认知是由一个复杂的分布式神经网络支撑的。本文回顾了我们在这一新兴图景中的贡献，并追溯了该网络中每个区域的假定作用。神经心理学研究表明，语义认知至少依赖于两个相互作用的组成部分：语义表示[在语义痴呆症（SD）中受损]和控制过程[在多模态语义障碍后的中风失语症（SA）患者中不足]。为了探索第一个组成部分，我们在健康志愿者中使用了失真校正功能磁共振成像（fMRI）和经颅磁刺激（TMS）：这些研究一致表明，前颞叶（ATL；在 SD 中萎缩）在一个无模态语义“枢纽”中结合了来自不同模式的信息。编码特定语义特征的皮质区域（“辐条”）也对特定类别中的知识做出了关键贡献。这个大脑区域网络与依赖左额下回（LIFG）、后颞中回（pMTG）和下顶叶皮质的语义控制过程相互作用。这些区域受损的 SA 患者在言语和非言语任务中都难以将注意力集中在与当前目标或上下文相关的知识上。LIFG 和颞顶损伤的 SA 患者表现出相似的语义控制缺陷，这表明一个大规模的分布式皮质网络支撑着语义控制。fMRI 和 TMS 再次提供了一致的证据。我们在 fMRI 中分别操纵语义任务的表示和控制需求，发现颞叶内存在分离：ATL 对检索到的意义数量敏感，而 pMTG 和 LIFG 则表现出语义选择的影响。此外，对 LIFG 和 pMTG 进行 TMS 会对等效于语义控制的任务产生干扰。下一个挑战是描绘语义控制网络中每个区域的具体作用，并指定控制过程与语义表示相互作用的方式，以将处理重点放在概念的相关特征上。
