Corrigendum: Evaluation of Metformin on Cognitive Improvement in Patients With Non-dementia Vascular Cognitive Impairment and Abnormal Glucose Metabolism - Lin, Yufeng; Wang, Kaiyuan; Ma, Chunchao; Wang, Xuesong; Gong, Zhongying; Zhang, Rui; Zang, Dawei; Cheng, Yan (Frontiers in Aging Neuroscience, 2018)