title: The Facilitative Effect of Transcranial Direct Current Stimulation on Visuospatial Working Memory in Patients with Diabetic Polyneuropathy: A Pre-post Sham-Controlled Study.
abstract: Diabetes mellitus can lead to diabetic polyneuropathy (DPN) and cognitive deficits that manifest as peripheral and central neuropathy, respectively. In this study we investigated the relationship between visuospatial working memory (VSWM) capacity and DPN severity, and attempted to improve VSWM in DPN patients via the use of transcranial direct current stimulation (tDCS). Sixteen DPN patients and 16 age- and education-matched healthy control subjects received Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) and Montreal Cognitive Assessment (MOCA) for baseline cognitive assessment. A forward- and backward-recall computerized Corsi block tapping task (CBT), both with and without a concurrent motor interference task was used to measure VSWM capacity. Each DPN patient underwent a pre-treatment CBT, followed by tDCS or sham treatment, then a post-treatment CBT on two separate days. We found that although patients with severe DPN (Dyck's grade 2a or 2b) showed comparable general intelligence scores on WAIS-IV as their age- and education-matched healthy counterparts, they nonetheless showed mild cognitive impairment (MCI) on MOCA and working memory deficit on digit-span test of WAIS-IV. Furthermore, patients' peripheral nerve conduction velocity (NCV) was positively correlated with their VSWM span in the most difficult CBT condition that involved backward-recall with motor interference such that patients with worse NCV also had lower VSWM span. Most importantly, anodal tDCS over the right DLPFC was able to improve low-performing patients' VSWM span to be on par with the high-performers, thereby eliminating the correlation between NCV and VSWM. In summary, these findings suggest that (1) MCI and severe peripheral neuropathy can coexist with unequal severity in diabetic patients, (2) the positive correlation of VSWM and NCV suggests a link between peripheral and central neuropathies, and (3) anodal tDCS over the right DLPFC can improve DPN patients' VSWM, particularly for the low-performing patients.
authors.affiliation: Institute of Clinical Medicine, College of Medicine, National Cheng Kung UniversityTainan, Taiwan; Department of Neurology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung UniversityTainan, Taiwan.
authors.forename: Yi-Jen
authors.initials: YJ
authors.lastname: Wu
authors.affiliation: Graduate Institute of Humanities in Medicine, Taipei Medical UniversityTaipei, Taiwan; Brain and Consciousness Research Center, Shuang Ho Hospital, Taipei Medical UniversityNew Taipei City, Taiwan.
authors.forename: Philip
authors.initials: P
authors.lastname: Tseng
authors.affiliation: Department of Neurology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University Tainan, Taiwan.
authors.forename: Han-Wei
authors.initials: HW
authors.lastname: Huang
authors.affiliation: Department of Psychology and Institute of Cognitive Science, College of Social Sciences, National Cheng Kung University Tainan, Taiwan.
authors.forename: Jon-Fan
authors.initials: JF
authors.lastname: Hu
authors.affiliation: Institute of Cognitive Neuroscience, National Central University Jhongli, Taiwan.
authors.forename: Chi-Hung
authors.initials: CH
authors.lastname: Juan
authors.affiliation: Department of Pharmacology, College of Medicine, National Cheng Kung University Tainan, Taiwan.
authors.forename: Kuei-Sen
authors.initials: KS
authors.lastname: Hsu
authors.affiliation: Department of Neurology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University Tainan, Taiwan.
authors.forename: Chou-Ching
authors.initials: CC
authors.lastname: Lin
keywords: Corsi block tapping task; diabetic polyneuropathy; dorsolateral prefrontal cortex; mild cognitive impairment; nerve conduction velocity; transcranial direct current stimulation; visuospatial working memory