Table_1_tDCS Facilitation of Picture Naming: Item-Specific, Task General, or Neither?.DOCX

The aim of the present study was to clarify the conditions under which anodal tDCS applied to left hemisphere language sites may facilitate picture naming latencies in healthy young adults. We built upon previous studies by directly testing for item-specific and generalized effects of tDCS through manipulation of item-familiarization and through testing for both online and offline effects of stimulation, in the same paradigm. In addition, we tested for the robustness of these effects by comparing two left hemisphere sites critical for lexical retrieval. Twenty-eight healthy young adults completed two testing sessions receiving either anodal (1.5 mA, 20 min) or sham stimulation (1.5 mA, 30 s) in each session. Half of the participants received tDCS over the left inferior frontal region and the other half over the left posterior superior temporal region. All participants were asked to a name a set of pictures and their response latencies were compared at three time points (before, during, and after the end of stimulation). The stimulus set was constructed so that some items were presented at all time points, some before and after stimulation, and some during stimulation only. A parsimonious linear mixed effects model (LMM) revealed robust repetition priming effects as latencies were reliably faster for previously named items in all conditions. However, active tDCS did not produce any additional facilitation in relation to sham, and even led to slower performance in the IFG group when the stimulated items differed from those tested at baseline and post-test. Our findings add to the present debate about the efficacy of single-session tDCS for modulation of lexical retrieval in healthy young adults. We conclude that future research should take a more systematic, step-wise approach to the application of tDCS to the study of language and that more sensitive experimental paradigms, which include a training element, are more adapted to the study of cognitive processes in populations with optimal levels of cortical excitability.

本研究旨在明确：将阳极经颅直流电刺激（anodal tDCS）作用于左半球语言功能脑区时，可促进健康青年成年人图片命名潜伏期的适用条件。本研究基于既往研究成果，在同一实验范式中，通过操纵项目熟悉度，并检测刺激的在线效应与离线效应，直接验证tDCS的项目特异性效应与泛化效应。此外，本研究通过比较两个与词汇提取密切相关的左半球脑区，检验了上述效应的稳定性。28名健康青年成年人完成了两次测试环节，每次测试分别接受阳极tDCS刺激（1.5 mA，20 min）或假刺激（1.5 mA，30 s）。其中半数参与者接受左侧额下回区域的tDCS刺激，另一半则接受左侧颞上回后部的刺激。所有参与者均需对一组图片进行命名，并在三个时间点——刺激前、刺激中及刺激结束后——比较其反应潜伏期。该刺激集的构建规则为：部分项目在全部三个时间点均呈现，部分仅在刺激前与刺激后呈现，剩余部分仅在刺激过程中呈现。简约线性混合效应模型（LMM）分析结果显示，重复启动效应显著：所有实验条件下，先前命名过的项目的反应潜伏期均显著缩短。然而，主动tDCS并未较假刺激产生额外的促进效应，甚至当刺激所用项目与基线及后测所用项目不一致时，额下回（inferior frontal gyrus, IFG）组的表现反而更慢。本研究结果进一步丰富了当前关于单次tDCS对健康青年成年人词汇提取调节效果的学术讨论。我们认为，未来的研究应采用更系统、循序渐进的方法开展tDCS在语言研究中的应用，且包含训练环节的高敏感性实验范式更适用于皮层兴奋性处于最优水平的人群的认知过程研究。