LAUSR

s Brain Stimulation 14 (2021) 1589e1707 glutamate and GABA in the left DLPFC using combined tDCS/MRS in healthy participants. Thus, this study extends our previous tDCS/MRSwork in other target regions (i.e. right DLPFC, medial PFC). Methods: Fourty-one healthy participants were screened and recruited. tDCS was applied inside an MRI Scanner using a neuroConn DC-Stimulator MR device. Active stimulation consisted of a 2mA electrical current delivered for a duration of 20 minutes, while the sham condition consisted only of a ramp-up/ramp-down sequence to induce tactile sensations. We recorded three MEGA-PRESS spectroscopy sequences before, during, and after stimulation with tDCS, as well as baseline and post-stimulation resting state fMRI sequences. Spectroscopy was analyzed using the software packages Gannet and LCModel to calculate GABA and Glutamate concentrations respectively. Results: Although an interim analysis with a notably small sample size revealed no significant differences between active and sham tDCS, the results for the full sample (N1⁄441) will be presented and further discussed together with a correction of neurotransmitter concentration using only grey matter tissue for MRS calculations. This work was supported by the German Center for Brain Stimulation (GCBS) research consortium (Work Package 5, grant number: 01EE1403E), funded by the Federal Ministry of Education and Research (BMBF).