Anodale transkranielle Gleichstromstimulation des linken dorsolateralen Präfrontalkortex bei Patienten mit leichter vaskulärer Demenz

In this study the effect of anodal transcranial direct current stimulation of the left dorsolateral prefrontal cortex in patients with vascular dementia was assessed. Previous studies have shown that transcranial direct current stimulation can improve various cognitive functions in patients with Alzheimer’s disease. Since the effect of transcranial direct current stimulation has not been evaluated in the context of vascular dementia, we performed a study targeting this population. 21 patients with mild vascular dementia diagnosed by the diagnosis criteria of the “National Institute of Neurological Disorders and Stroke” and the “Association Internationale pour la Recherche et l’Enseignement en Neurosciences” and a “Mini-Mental-State-Examination” score of 20-26 points were randomized into a verum group and a sham group. The study was performed using a single blinded, placebo-controlled parallel group design. Patients received four sessions of either anodal or sham transcranial direct current stimulation of the the left dorsolateral prefrontal cortex, using the electroencephalographic F3 position for four consecutive days. Current strength was set at 2 milliampere, the cathode was placed over the contralateral supraorbital area. Stimulation was single blinded. For screening purposes, “Mini-Mental-State-Examination” and the “Geriatric Depression Scale” were used to determine if patients met the inclusion criteria that were defined prior to the beginning of the study. Cognitive testing was performed before and after the first stimulation, after the last stimulation at day four and two weeks after the last stimulation as a follow-up. It consisted of a 2-back task, a Go/NoGo task, a picture naming task and the cognitive subscale of the “Alzheimer’s Disease Assessment Scale“, as a tool for detecting clinical relevant changes. “Clinical Global Impression-Improvement” was used as a self-rating scale to monitor subjective improvements. Statistical analysis revealed no significant group differences between patients receiving verum vs. sham stimulation regarding age, Mini-Mental-State-Examination score or Geriatric Depression Scale score. Statistical analysis for the 2-back task, the cognitive subscale of Alzheimer’s Disease Assessment Scale and Go/NoGo was performed using Analysis of variance with repeated measures and respective post-hoc tests. Since Kolmogorov-Smirnov tests revealed that some parameters of the Go/NoGo task were not normally distributed, the (nonparametric) Friedman test was used for analysis. The number of memorized words in the picture naming task mproved in the anodal group compared with the control group at the 2 weeks follow-up. Reaction time of the 2-back task and the Go/NoGo task improved in the anodal group after the last stimulation session. This effect was maintained until follow-up for the Go/NoGo task. Both verum and sham transcranial direct current stimulation reduced the score in the cognitive subscale of Alzheimer’s Disease Assessment Scale and decreased the number of omissions in the Go/NoGo task at the end of the stimulation. The score in Clinical Global Impression-Improvement was similar for the two stimulation conditions: On average, patients indicated minimal improvement of subjective state after both verum and sham stimulation after the last stimulation. In summary, anodal transcranial direct current stimulation improved visual recognition memory, verbal working memory and executive control. In particular, reaction time improved, which could be due to the fact that vascular dementia is characterized by a general deceleration of cognitive functions and, therefore, the improvement in reaction time could be the parameter standing out most in cognitive testing. Some limitations to this study need to be addressed. The sample size was rather small and slightly unbalanced, and we used a single-blinded instead of a double-blinded design. Repetitive cognitive testing may have lead to a training effect, especially seen in the cognitive subscale of Alzheimer’s Disease Assessment Scale. A specific cognitive training protocol was not applied in this study, so only limited conclusions can be drawn on the synergic effects of transcranial direct current stimulation and cognitive training. This first study, investigating the cognitive effects of transcranial direct current stimulation in patients with vascular dementia, showed promising results. Selective improvement after anodal transcranial direct current stimulation was found in visual recognition memory, verbal working memory and executive control. There are still many questions to be answered concerning action mechanism and application. Future studies should also address therapeutic approaches of combined protocols of cognitive training and transcranial direct current stimulation.