Human Cortical Physiology and Stroke Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Neuropsychologia. 2012 Feb;50(3):396-402. doi: 10.1016/j.neuropsychologia.2011.12.011. Epub 2011 Dec 27.
Transcranial magnetic stimulation and neuroimaging data have revealed bilateral posterior parietal cortex (PPC) involvement during verbal n-back working memory (WM). In this task as n (i.e., WM load) increases, subjects show poorer behavioral performance as well as greater activation of this brain area. Moreover, there is evidence that a brief period of practice or even increased familiarity with the task can improve WM performance and lead to activation changes in the PPC. The aim of this study was to investigate, using transcranial direct current stimulation (tDCS), the effects on WM load performance induced by different PPC modulation after increased familiarity with the task. After a short practice, we tested verbal WM using an n-back task (1-back vs. 2-back) before and after the application of bilateral tDCS over PPCs (left anodal-right cathodal, left cathodal-right anodal or sham). ANOVA showed a significant interaction between tDCS and task. In the 1-back task, left anodal-right cathodal modulation abolished improvement in reaction times observed in the other two modulation conditions. Conversely, in the 2-back task the same effect was observed after left cathodal-right anodal modulation relative to the other two modulation conditions. This double dissociation demonstrates either a differential engagement of each PPC or changes in the interhemispheric balance of activity across this brain region. Neuroimaging studies show parametric activation of the PPC as difficulty increases, but activation does not switch sides. Thus, our observed effects cannot be attributed to increased task difficulty, the stimuli used, or the response requirements. Rather, we suggest that these findings reflect the use of different processing strategies to perform these two tasks. In conclusion, after increased familiarity with the task, different tDCS modulations lead to changes in a task-related region depending on differences in processing strategies in 1-back vs. 2-back.
经颅磁刺激和神经影像学数据显示，在言语 n 回工作记忆（WM）中双侧顶后皮质（PPC）参与。在这项任务中，随着 n（即 WM 负荷）的增加，受试者的行为表现会变差，该脑区的激活也会增加。此外，有证据表明，短暂的练习甚至增加对任务的熟悉度可以提高 WM 表现，并导致 PPC 中的激活变化。本研究旨在通过经颅直流电刺激（tDCS）研究在增加对任务的熟悉度后，不同 PPC 调节对 WM 负荷表现的影响。在短暂的练习后，我们在应用双侧 tDCS 于 PPC 之前和之后（左阳极右阴极、左阴极右阳极或假刺激），使用 n 回任务（1 回对比 2 回）测试言语 WM。方差分析显示 tDCS 和任务之间存在显著的交互作用。在 1 回任务中，左阳极右阴极调节消除了在其他两种调节条件下观察到的反应时改善。相反，在 2 回任务中，相对于其他两种调节条件，在左阴极右阳极调节后观察到相同的效果。这种双重分离表明，每个 PPC 的参与度不同，或者整个大脑区域的活动的左右半球平衡发生变化。神经影像学研究表明，随着难度的增加，PPC 的参数激活，但激活不会切换到另一侧。因此，我们观察到的效果不能归因于任务难度的增加、所使用的刺激或反应要求的增加。相反，我们认为这些发现反映了使用不同的处理策略来执行这两个任务。总之，在增加对任务的熟悉度后，不同的 tDCS 调节会导致与任务相关的区域发生变化，这取决于在 1 回对比 2 回任务中处理策略的差异。
