Effects of multisession transcranial direct current stimulation as an augmentation to cognitive tasks in patients with neurocognitive disorders in Japan: a study protocol for a randomised controlled trial

IntroductionTranscranial direct current stimulation (tDCS) is a potentially novel strategy for cognitive enhancement in patients with disorders. We present a study protocol for a randomised controlled trial designed to evaluate the safety and efficacy of tDCS combined with cognitive tasks on cognition in such patients.Method and analysisThis is a two-arm, parallel-design, randomised, sham-controlled trial, in which participants and raters will be blinded at a single centre. Stratified randomisation will be conducted, and a randomisation sequence will be generated through the Electronic Data Capture system. Patients who met the Diagnostic and Statistical Manual of Mental Disorders-5 criteria for neurocognitive disorders will be recruited and randomised to receive either active (2 mA for 20 min) or sham (stimulation ramped up and down for 1 min) stimulation in 10 sessions over five consecutive days. A direct current will be transferred by a 35 cm2 saline-soaked sponge electrode. An anode will be placed over the left dorsolateral prefrontal cortex, and a cathode will be placed over the right supraorbital cortex. Calculation tasks will be conducted in both arms as a cognitive task for 20 min during the stimulation. This task consists of basic arithmetic questions, such as single-digit addition, subtraction, multiplication and division. The primary outcome will be the mean change in the Alzheimer Disease Assessment Scale–cognition at Day 5 after baseline. Depressive symptoms, as measured by the geriatric depression scale, and quality of life, as measured by the Medical Outcomes Study 36-item Short-Form Health Survey, will also be assessed. Data will be collected at baseline, within 3 days following the final stimulation and 1 month thereafter. The estimated sample size is 46 per group based on the assumptions that an estimated mean difference is −1.61 and SD is 2.7. Mixed models for repeated measures will be used for the statistical analysis.Ethics and disseminationThe National Center of Neurology and the Psychiatry Clinical Research Review Board (CRB3180006) approved this study. The results of this study will be published in a scientific peer-reviewed journal.Trial registration detailsJapan Registry of Clinical Trials jRCTs032180016.