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Introduction. Non-invasive neuromodulation via transcranial direct current stimulation (tDCS) is a promising method for modulating plasticity. For the first time multichannel tDCS was used to investigate a larger number of children and young adolescents. Previous studies suggest that tDCS affects cognitive functions. It is assumed that the inferior frontal gyrus (IFG) has an important role in the process of response inhibition. Therefore, multichannel tDCS might has potential as therapy option for neurodevelopmental diseases such as attention deficit hyperactivity disorder (ADHD). The present study addressed the question whether tDCS could modulate this function. In addition, the study intended to investigate the most effective timing and tolerance of stimulation. Methods. The study was approved by the Ethic Committee of the Faculty of Medicine of Kiel university. 29 healthy participants (10-17 years old, mean age: 14,2 years, SD 2,14) were included in the analysis in a double-blinded and sham-controlled crossover study. The Flanker-task was used as target-task so that reaction time and accuracy were focused in the evaluation. Stimulation was scheduled prior (offline) or during (online) target task. After that the participants completed the n-back-task and the CPT-task as non-target-tasks. Resting state EEG was recorded before and after stimulation. Additionally, task related EEG was performed to expose changes at the neurophysiological level. For multichannel 2 mA tDCS over the right IFG we used a 6-channel solution (3.14 cm2 circular electrodes, positioned at F8 (1000 µA), FC6 (999 µA), P7 (−377 µA), T8 (−422 µA), C6 (−577 µA) and FPZ (−623 µA), filled with EEG electrode gel). Current was ramped up for 30 seconds at the beginning and the end in sham as well in verum stimulation. A linear mixed model was used for statistical evaluation. Results. There were only a few participants showing side effects such as itching, burning or fatigue. In a total of 112 sessions there were eight cases of adverse events such as headache. Our preliminary results at the behavioural level show no significant differences (p > 0.05) between tDCS and sham stimulation. There were no significant effects on accuracy or reaction time between online or offline stimulation neither. Conclusion. Our results show that tDCS was tolerated well by the participants. Based on preliminary results we could not confirm that tDCS could modulate the rIFG because response inhibition was not affected significantly. Further analysis could find out about possible reasons for our results such as ceiling effects. Analysis of resting EEG prior and after stimulation as well as task related EEG might yield neurophysiological explanation for the absence of behavioural improvement outcomes. The results provide a basis for future studies such as investigations of ADHD patients and might offer a compatible therapy option.

Introduction. Transcranial direct current stimulation (tDCS) is a non-invasive method of modulating brain activity. Previous studies with common tDCS montages have shown that there are positive effects on the left inferior dorsolateral prefrontal cortex (lDLPFC) for both healthy and clinical population like improvement of the working memory. Nevertheless, there is still lack of clear guidelines and safety instructions, probably due to not specific enough simulation montages, especially when focusing on pediatric population. This study aims to investigate behavioral outcome of multichannel tDCS over the lDLPFC in healthy children and adolescents. Therefore, tDCS was coupled with a memory task, especially focusing on accuracy and reaction time changes. Methods. The study was approved by the Ethic Committee of the Faculty of Medicine of Kiel University. The study was conducted in a double-blinded, randomized, sham-controlled design. 28 healthy children and adolescents (Age range: 10–17 years, mean age = 14,18, SD = 2,23) were included in the analysis. In four separate sessions, they received multichannel 2 mA anodal or sham tDCS for 20 minutes over the left DLPFC before or during working memory task (2 back task). At the behavioral level response time and accuracy for N-back task were evaluated. Additionally, safety and tolerability of multichannel tDCS has been investigated by written questionnaires. For multichannel 2 mA tDCS over DLPFC we used a 6-channel solution (3.14 cm2 circular electrodes; AF3 (897 μΑ), AF7 (284 μΑ), F3 (819 μΑ), Fp2 (−1000 μΑ) und T7 (−1000 μΑ)). Before, during and after stimulation 32 channel EEG was recorded in order to demonstrate neurophysiological changes. All materials required for the stimulations and EEG recording were obtained from Neuroelectrics (Barcelona, Spain). Results. All participants tolerated the stimulation well. Our preliminary behavioral results showed that there were no significant effects on accuracy (ACC) or reaction time (RT) compared tDCS to sham stimulation. There were also no significant effects on ACC and RT between online or offline stimulation and no significant effects in the interaction of these variables (p > 0.05). Conclusion. In summary, our study demonstrates that multichannel tDCS over DLPFC with 2 mA intensity over 20 min is well tolerated, and thus may be used as an experimental and treatment method in the pediatric population. Based on preliminary behavioral data, we could not show any stimulation effect. In accordance to literature though, stimulation often shows bigger effects on clinical population rather than healthy participants. Possible reasons for null findings could be ceiling effects (e.g. Suitability of the Paradigm depending on age). Furthermore, individual differences like baseline activity, may have had an impact on stimulation effectivity. Additional EEG analysis may provide more specific insights into developmental aspects of working memory processing on the neural level.