The Effect of tES on a Cognitive Training

As other studies have shown, transcranial direct current stimulation (tDCS) can improve the outcome of memory tasks in Alzheimer's disease (AD), mild cognitive impairment (MCI) and healthy older adults. Only few studies have investigated the effect of the combination of tDCS and a simultaneous cognitive training and to the investigators' knowledge there is no comparison of tDCS and transcranial alternating current (tACS) effects during a cognitive training or for different populations. With results from this study existing trainings can be optimised. In total 180 participants are planned to be included in this study. This number is based on a g\*Power estimation. According to this estimation the study has to include 153 participants. Regarding similar studies the investigators assume a dropout rate of 15% resulting in a total of 180 participants (60 AD patients, 60 MCI patients and 60 healthy older adults) This number should make it possible to find the expected mild effects reported in literature. A mixed-effects ANOVA model with the between-subjects factor stimulation (tDCS, tACS, sham) and the within-subjects factor time will be computed.