Mild cognitive impairment (MCI) is a pre-clinical stage of Alzheimer's disease (AD). In recent years, transcranial direct current stimulation (tDCS), as a neuromodulation technique, has being applied in the field of cognitive intervention for MCI, but its effect is controversial because of many factors. In order to promote the application of tDCS in intervention for MCI, this study performed a systematic review of the previous studies that used tDCS to improve cognitive functions of MCI individuals. The results indicate that tDCS could improve episodic memory, working memory, and language of individuals with MCI, while there is a lack of strong evidence that supports a positive effect of tDCS on attention of individuals with MCI. The placement of electrodes, time course of treatment, and current intensity all affected the intervention effect of tDCS. Future studies should take brain networks underlying cognitive processes and personalized factors such as age and education level into consideration to design better stimulation protocols, and they should be conducted in combination with neuroimaging technologies to evaluate the intervention effect of tDCS more accurately and objectively and to discover the neural mechanisms of tDCS intervention.

Subjective memory decline is one of the most common symptoms reported in the elderly,which is considered as a high-risk factor for dementia.This article presented an overview of an update of definition and epidemiology of subjective memory decline,reviewed its risk factors,and summarized neuroimaging changes in brain structure and function.Finally,some suggestions for future research were also proposed.