Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
Brain. 2013 Apr;136(Pt 4):1245-59. doi: 10.1093/brain/awt019. Epub 2013 Mar 7.
It is notoriously difficult to name odours. Without the benefit of non-olfactory information, even common household smells elude our ability to name them. The neuroscientific basis for this olfactory language 'deficit' is poorly understood, and even basic models to explain how odour inputs gain access to transmodal representations required for naming have not been put forward. This study used patients with primary progressive aphasia, a clinical dementia syndrome characterized by primary deficits in language, to investigate the interactions between olfactory inputs and lexical access by assessing behavioural performance of olfactory knowledge and its relationship to brain atrophy. We specifically hypothesized that the temporal pole would play a key role in linking odour object representations to transmodal networks, given its anatomical proximity to olfactory and visual object processing areas. Behaviourally, patients with primary progressive aphasia with non-semantic subtypes were severely impaired on an odour naming task, in comparison with an age-matched control group. However, with the availability of picture cues or word cues, odour matching performance approached control levels, demonstrating an inability to retrieve but not to recognize the name and nature of the odorant. The magnitude of cortical thinning in the temporal pole was found to correlate with reductions in odour familiarity and odour matching to visual cues, whereas the inferior frontal gyrus correlated with both odour naming and matching. Volumetric changes in the mediodorsal thalamus correlated with the proportion of categorical mismatch errors, indicating a possible role of this region in error-signal monitoring to optimize recognition of associations linked to the odour. A complementary analysis of patients with the semantic subtype of primary progressive aphasia, which is associated with marked temporopolar atrophy, revealed much more pronounced impairments of odour naming and matching. In identifying the critical role of the temporal pole and inferior frontal gyrus in transmodal linking and verbalization of olfactory objects, our findings provide a new neurobiological foundation for understanding why even common odours are hard to name.
命名气味是出了名的困难。如果没有非嗅觉信息的帮助，即使是常见的家庭气味也会让我们无法命名。这种嗅觉语言“缺陷”的神经科学基础理解得很差，甚至没有提出基本的模型来解释气味输入如何获得命名所需的跨模态表示。本研究使用原发性进行性失语症患者（一种以语言为主要特征的痴呆综合征），通过评估嗅觉知识的行为表现及其与大脑萎缩的关系，来研究嗅觉输入与词汇获取之间的相互作用。我们特别假设，由于 temporal pole 与嗅觉和视觉物体处理区域的解剖关系接近，因此它在将气味物体表示与跨模态网络联系起来方面发挥关键作用。行为上，与年龄匹配的对照组相比，具有非语义亚型的原发性进行性失语症患者在气味命名任务中严重受损。然而，有了图片提示或单词提示，气味匹配表现接近对照组水平，这表明他们无法检索但可以识别气味的名称和性质。发现 temporal pole 的皮质变薄程度与气味熟悉度和与视觉线索的气味匹配减少相关，而 inferior frontal gyrus 与气味命名和匹配都相关。中脑背侧丘脑的体积变化与分类不匹配错误的比例相关，表明该区域可能在错误信号监测中起作用，以优化与气味相关的关联的识别。对原发性进行性失语症语义亚型患者（与颞极明显萎缩相关）的补充分析显示，气味命名和匹配的损伤更为明显。在确定 temporal pole 和 inferior frontal gyrus 在跨模态连接和嗅觉物体的言语化中的关键作用时，我们的发现为理解为什么即使是常见的气味也难以命名提供了新的神经生物学基础。
