Abstract: With the development of social economy, there is growing interest in methods and techniques for improving cognitive functions. Among these methods and techniques, as a low-cost, efficient and noninvasive brain stimulation method, transcranial direct current stimulation (tDCS) is a promising neuroenhancement technique which is especially suitable for practical applications in healthy populations. The aim of this review is to introduce recent studies on the application of tDCS to enhance the cognitive function of healthy individuals and briefly discuss the potential influencing factors of tDCS in cognitive enhancement. tDCS involves passing weak electric currents on the scalp to modulate the resting potentials of underlying neural tissue. The study of motor-evoked potentials showed that anodal tDCS could enhance the cortical excitability, and cathodal tDCS could decrease the cortical excitability. However, the neural underpinnings of tDCS effects on cognitive task performance still remain elusive. The network activity-dependent model shows that the cognitive enhancement effect of tDCS depends on the interaction of many factors, including tDCS protocol, cognitive task and task-related neural network. tDCS has been found to modulate many cognitive components. Here, we focus on the enhancement effects of tDCS on perception, attention, memory, learning and multitasking. First, tDCS studies on perception were performed for visual, auditory and pain perception. For visual and auditory perception, the studies applied tDCS over the visual cortex, auditory cortex and primary somatosensory cortex. For pain perception, tDCS can regulate pain perception in two ways: the first is to increase the pain threshold by modulating the cortical excitability of the sensory cortex and the motor cortex. The second is to relieve the pain by adjusting the cortical excitability of the dorsolateral prefrontal cortex (DLPFC). Secondly, the studies aimed to explore the enhancement of attention applied tDCS over the DLPFC and the parietal cortex (PC). Different aspects of attention have been investigated, such as alerting, orientation, internal and external attention. Third, the effect of tDCS on memory have been reported with tDCS over the frontal and parietal cortex. Many studies have focused on improving working memory, as well as demonstrating the effect of tDCS on long-term memory. Fourth, tDCS studies on learning have explored the enhancement of vocabulary learning, motion learning and perceptual learning. Due to the diversity of learning content, the effect on the task and tDCS protocol are different. Finally, some studies have shown that tDCS over the frontal cortex can improve multitasking. These results indicate the causal relationship between the frontal cortex and cognitive functions, including executive function and cognitive control. On the basis of retrospective study, we conclude that tDCS as a tool to improve the cognitive ability of healthy volunteers has an important prospect. However, the coherence of the evidence base and the translational potential of these findings are currently constrained by a number of factors, including stimulus parameters and individual differences. In the future research, there are still many important issues to be further explored: Firstly, the physiology mechanism under tDCS effect is still unclear; Secondly, standard stimulation parameters should be established; Thirdly, the use of high-definition tDCS or the combination of tDCS and other high-technology, can further improve the spatial resolution of tDCS; Finally, the tDCS effect on children and the elderly deserves to be explored.

Key words: Cognitive enhancement, Transcranial direct current stimulation, Perception, Attention, Memory, Learning, Complex task

摘要： 经颅直流电刺激作为一种无创脑刺激技术，已在临床治疗及康复领域有广泛应用。随着研究的深入和人类对于自身认知需求的提高，近年来也有研究者开始尝试使用该技术增强健康个体的认知功能。本文从感知觉、注意、记忆、学习和复杂任务五个方面对目前经颅直流电刺激技术在健康个体认知增强领域的研究现状进行梳理和总结，讨论了机制和影响因素，以及未来面临的问题和挑战。

关键词: 认知增强 经颅直流电刺激 感知觉 注意 记忆 学习 复杂任务