Baciu M, Boudiaf N, Cousin E, Perrone-Bertolotti M, Pichat C, Fournet N, Chainay H, Lamalle L, Krainik A
Univ. Grenoble Alpes, LPNC, F-38040, Grenoble, France.
CNRS, LPNC UMR 5105, F-38040, Grenoble, France.
Age (Dordr). 2016 Feb;38(1):3. doi: 10.1007/s11357-015-9857-y. Epub 2015 Dec 28.
This fMRI study aimed to explore the effect of normal aging on word retrieval and generation. The question addressed is whether lexical production decline is determined by a direct mechanism, which concerns the language operations or is rather indirectly induced by a decline of executive functions. Indeed, the main hypothesis was that normal aging does not induce loss of lexical knowledge, but there is only a general slowdown in retrieval mechanisms involved in lexical processing, due to possible decline of the executive functions. We used three tasks (verbal fluency, object naming, and semantic categorization). Two groups of participants were tested (Young, Y and Aged, A), without cognitive and psychiatric impairment and showing similar levels of vocabulary. Neuropsychological testing revealed that older participants had lower executive function scores, longer processing speeds, and tended to have lower verbal fluency scores. Additionally, older participants showed higher scores for verbal automatisms and overlearned information. In terms of behavioral data, older participants performed as accurate as younger adults, but they were significantly slower for the semantic categorization and were less fluent for verbal fluency task. Functional MRI analyses suggested that older adults did not simply activate fewer brain regions involved in word production, but they actually showed an atypical pattern of activation. Significant correlations between the BOLD (Blood Oxygen Level Dependent) signal of aging-related (A > Y) regions and cognitive scores suggested that this atypical pattern of the activation may reveal several compensatory mechanisms (a) to overcome the slowdown in retrieval, due to the decline of executive functions and processing speed and (b) to inhibit verbal automatic processes. The BOLD signal measured in some other aging-dependent regions did not correlate with the behavioral and neuropsychological scores, and the overactivation of these uncorrelated regions would simply reveal dedifferentiation that occurs with aging. Altogether, our results suggest that normal aging is associated with a more difficult access to lexico-semantic operations and representations by a slowdown in executive functions, without any conceptual loss.
这项功能磁共振成像（fMRI）研究旨在探讨正常衰老对词汇检索和生成的影响。所解决的问题是词汇生成能力的下降是由直接机制决定的，该机制涉及语言操作，还是由执行功能的下降间接导致的。实际上，主要假设是正常衰老不会导致词汇知识的丧失，只是由于执行功能可能下降，词汇处理中涉及的检索机制普遍放缓。我们使用了三项任务（言语流畅性、物体命名和语义分类）。测试了两组参与者（年轻人，Y组和老年人，A组），他们没有认知和精神障碍，且词汇水平相似。神经心理学测试显示，老年参与者的执行功能得分较低，处理速度较慢，言语流畅性得分往往也较低。此外，老年参与者在言语自动化和过度学习信息方面得分较高。在行为数据方面，老年参与者的表现与年轻成年人一样准确，但在语义分类任务中明显较慢，在言语流畅性任务中流畅性较差。功能磁共振成像分析表明，老年人并非简单地激活较少参与词汇生成的脑区，而是实际上表现出一种非典型的激活模式。与衰老相关区域（A组 > Y组）的血氧水平依赖（BOLD）信号与认知得分之间的显著相关性表明，这种非典型的激活模式可能揭示了几种补偿机制：（a）由于执行功能和处理速度下降，克服检索放缓；（b）抑制言语自动过程。在其他一些与衰老相关区域测量的BOLD信号与行为和神经心理学得分无关，这些不相关区域的过度激活仅仅表明衰老过程中发生的去分化。总之，我们的结果表明，正常衰老与执行功能放缓导致的词汇语义操作和表征获取更加困难相关，而没有任何概念性损失。
