工作记忆刷新及其训练效应——经颅直流电刺激的作用

工作记忆刷新是执行功能的重要成分之一。以往研究结合n-back任务和经颅直流电刺激（transcranial direct current stimulation ,tDCS）技术探究刷新能力，发现tDCS技术能够一定程度上增强刷新训练效果并引起大脑神经元相关活动的变化，其增强效果能够维持一定的时间，且能够迁移到其他认知任务之中。但tDCS的干预效果在各项研究中存在一定的差异性。其作用效果会受到训练任务与训练方式、电流强度、电极布局和训练时间间隔等因素的影响。未来研究可以探索tDCS结合刷新训练的最佳刺激参数，以获得最优化的干预效果。

Working memory updating and its training effect: the role of transcranial direct current stimulation

Working memory updating is an important part of executive function. It refers to the ability to monitor and code new input information in working memory, replace old information with new information, and modify the content of working memory. Previous studies showed that working memory updating could be enhanced via training and transcranial direct current stimulation (tDCS). The improvement of working memory updating has gradually become a hot research topic in the field of cognitive psychology. Here, this review considered the current state of the emerging single-session tDCS and multi-session tDCS coupled with updating literature, and highlighted multi factors that could influence the intervention effect of tDCS on updating, and finally discussed the application and prospect of tDCS coupled with updating training. As one of the non-invasive brain stimulation techniques, tDCS can increase or decrease cortical excitability of local brain areas by modulating NMDA ( N-methyl-D-aspartate) activity. A growing field of cognitive training studies has indicated that tDCS might be a possible way to improve cognitive ability. Neuroimaging studies has also revealed that tDCS could alter neural activities. Therefore, working memory enhancement using tDCS has attracted increased attention over longer time periods. A considerable quantity of single-session studies using tDCS revealed that stimulating left dorsolateral prefrontal cortex (DLPFC) could improve verbal updating ability and stimulating right DLPFC could enhance the performance in spatial updating task. Besides, they showed that tDCS could alter working memory performance by modulating the underlying oscillatory brain activity (like alpha bands, theta bands). Although most published studies have provided positive findings, some meta-analysis studies indicated that the efficacy of single-session tDCS on working memory had no evidential value after publication bias correction. This does not mean that the effect of tDCS on working memory updating was invalid. They also showed that frontoparietal network stimulation coupled with working memory updating training might be a promising intervention to improve updating ability. Some studies found that anodal tDCS coupled with n-back training could effectively improve the performance in updating tasks and induce changes in the neuronal regulatory activity. The enhancement effect could be maintained for a certain period and could also transfer to untrained high-order cognitive tasks (like influent intelligence, attention and mathematical). Importantly the emerging literature revealed that notable inconsistency in the effect of tDCS for updating training was observed in various studies. The intervention effect of tDCS could be affected by different parameters, like training tasks, training methods, transfer tasks, follow-up test, stimulation intensity, montage and training spacing. In addition, individual difference (like baseline ability) might be an important factor that affect the efficacy of tDCS on working memory updating. Further studies can focus on this factor and explore the effect of tDCS on working memory updating training across various individuals. Moreover, an important direction for further work might be to study the optimal stimulation parameters (tDCS protocols, training procedure, transfer task selection and follow-up test) with regard to pairing tDCS with working memory updating training so as to obtain the optimal intervention effect. Finally, the ethical issue of tDCS should be considered in future studies.