Wildgruber D, Kischka U, Ackermann H, Klose U, Grodd W
Section Experimental MR of the CNS, Department of Neuroradiology, University of Tübingen, Hoppe-Seyler-Str. 3, 72076, Tübingen, Germany.
Brain Res Cogn Brain Res. 1999 Jan;7(3):285-94. doi: 10.1016/s0926-6410(98)00031-7.
An impaired ability to recite highly automated word strings (e.g., the names of the months of the year) in reverse order concomitant with preserved production of the conventional sequence has been considered a salient sign of frontal lobe dysfunction. Using functional magnetic resonance imaging (fMRI), the spatial and temporal pattern of brain activation during covert performance of these tasks was evaluated in healthy subjects. As compared to the response obtained during forward recitation, re-sequencing of the word string yielded additional activation of the bilateral middle and inferior frontal gyri, the posterior parietal cortex and the left anterior cingulate gyrus. The prefrontal responses are in accordance with the clinical findings referred to. However, the set of activated areas, as a whole, presumably reflects contribution of the various components of the working memory system to the sequencing of word strings. During successive periods of task administration, subjects showed a linear increase of production speed. Analysis of corresponding dynamic changes of regional hemodynamic responses revealed a significant increase at the level of the left inferior parietal cortex and a decrease within the mesial aspect of the left superior frontal gyrus. Presumably, the former finding reflects increasing demands on the phonological short-term memory store, due to faster updating of its content under increased word production rate. Decreasing activation within the superior frontal gyrus might indicate contribution of this area to the initiation of the cognitive processes subserving the sequencing of verbal items. These findings demonstrate the capability of fMRI as a powerful tool for the analysis of dynamic brain activation.
不能以相反顺序背诵高度自动化的单词串（例如一年中的月份名称），而常规顺序的背诵能力却保留完好，这被认为是额叶功能障碍的一个显著迹象。利用功能磁共振成像（fMRI），在健康受试者中评估了这些任务隐蔽执行期间大脑激活的空间和时间模式。与正向背诵时获得的反应相比，单词串的重新排序产生了双侧额中回和额下回、顶叶后皮质以及左侧前扣带回的额外激活。前额叶的反应与所提及的临床发现一致。然而，作为一个整体，激活区域集大概反映了工作记忆系统的各个组成部分对单词串排序的贡献。在连续执行任务的期间，受试者的生成速度呈线性增加。对区域血流动力学反应的相应动态变化分析显示，左侧顶叶下部皮质水平有显著增加，而左侧额上回内侧部分有减少。大概，前一个发现反映了由于在单词生成率增加的情况下其内容更新更快，对语音短期记忆存储的需求增加。额上回内激活的减少可能表明该区域对支持言语项目排序的认知过程的启动有贡献。这些发现证明了fMRI作为分析大脑动态激活的有力工具的能力。
