Back task
The 2-back task was programmed in E-prime 2.0 software (Psychology Software, Tools Inc., USA). The visual stimulus consisted of letters (A to Z) that appeared in a pseudo-randomized order on a computer screen of 15 inches. The applied protocol consisted of three blocks of 30 letters. Letters were displayed on the screen for 500 ms, with an interval of 3000 ms between displays. Each block consisted of 10 ‘target' letters, representing a total of 30 ‘targets'. Targets were letters identical to the ones presented two steps earlier in the trial sequence. Participants were instructed to press different keys on the keyboard for target (key ‘2') and non-target (key ‘0') stimuli. A brief practice containing 20 stimuli was conducted prior to the task. The 2-back task was chosen because it was previously associated with working memory improvement after NIBS in healthy participants (