Effects on cognition of 20-day anodal transcranial direct current stimulation over the left dorsolateral prefrontal cortex in patients affected by mild cognitive impairment: a case-control study

Background: Mild cognitive impairment (MCI) is a common disorder affecting as much as 15% of the elderly population. Transcranial direct current stimulation (tDCS) is a non-invasive technique of neuromodulation that has proven to influence performance in different cognitive domains. Objective/hypothesis: We investigated the effects on cognition of 20-day anodal tDCS in 17 MCI patients compared with 17 matched MCI patients. Methods: Patients underwent neuropsychological evaluation at baseline and then were randomly assigned to the anodal or sham group. The tDCS protocol consisted in 20 min, 5 days per week (up to a total of 20 days), of 2-mA anodal stimulation over the left dorsolateral prefrontal cortex (DLPFC). The location of anodal electrode was chosen in accordance with previous reports which relate anodal stimulation of this site with cognitive enhancement. At the end of the last day of stimulation, a second neuropsychological evaluation was performed. We compared baseline and post-stimulation neuropsychological results in the anodal vs sham group using repeated measures ANOVA as a statistical analysis test. Results: At follow-up, patients exposed to anodal stimulation showed improvement in episodic verbal memory (p < 0.001) and figure naming test (p < 0.01), in a general index of cognitive function (Brief Mental Deterioration Battery) (p < 0.0001) and in a mood measurement test (Beck Depression Inventory) (p < 0.01). Conclusion: Anodal tDCS could be a useful tool to improve cognitive symptoms in MCI although more evidence is needed to understand the exact underlying mechanisms. Confirmation of its potential benefits in MCI would be significant.