P66. Laterality dependent effects of transcranial direct current stimulation (tDCS) on learning- and transfer-outcomes of a working memory training

Abstract

Background Working memory is the basis of various cognitive functions and has a strong connection to cognitive control and executive functions. Imaging studies revealed the dorsolateral prefrontal cortex (DLPFC) as a crucial cortical structure regarding working memory functioning. While many neuropsychiatric disorders, e.g. schizophrenia, ADHS and dementia, are accompanied by deficits in working memory, effective therapeutic interventions are currently absent. Therefore, working memory trainings appeared as a potential intervention, especially when combined with non-invasive brain stimulation techniques to enhance the efficiacy of aforementioned training paradigms. Several studies were able to demonstrate, that anodal tDCS of the DLPFC can indeed enhance working memory performance during stimulation. Although, the results regarding enhancement of a training itself are less decisive. This is especially true concercing augmentation of transfer effects, i.e. performance gains on untrained tasks. It is also unclear, which role is assigned to the fit of stimulus modality of the training paradigm (spatial vs. verbal) and the laterality of electrode placement (left vs. right DLPFC). Method In the current randomized, placebo-controlled study, 36 healthy, right-handed young adults participated and were split into three groups (anodal stimulation left DLPFC, anodal stimulation right DLPFC, sham-stimulation). Participants in the experimental groups recieved stimulation of 1 mA for 20 min during completion of training sessions. The training paradigm consisted of five session, i.e. pre-session, three training sessions and post-session. On the pre- and post-session participants were tested on an adaptive spatial n-back task, a verbal 3-back task and the digit- and block-span tasks of the WMS-R. Training task of the three training sessions was the adaptive spatial n-back task. Results and discussion We were able to demonstrate that stimulation of the left as well as the right DLPFC enhances working memory performance during training sessions, i.e. enhanced within-session learning. Regarding the trained spatial n-back task, persistent effects of tDCS (differences in performance gains between pre and post session as well as between-session learning) were not detected, regardless of stimulation laterality ( Fig. 1 ). However, tDCS of the right DLPFC resulted in an increased performance improvement (pre- vs. post-training) on the untrained verbal 3-back task ( Fig. 2 ). Therefore we conclude that tDCS is able to facilitate training of working memory and transfer of training effects to an untrained task. The lack of persistent effects on the trained spatial n-back task is most likely due to ceiling effects. Ongoing studies test that this approach can yield therapeutic effects in disorders associated with deficits of working-memory or DLPFC-function.