Schematic representation of the experimental procedure. (A) Illustrated is one of two sessions composing the within-subject sham-controlled design. Each session started with questionnaires followed by the physical motor task. After the physical motor task electrodes were placed over the Opponens Pollicis and First Dorsal Interossei of each hand to record surface EMG. Next stimulation was delivered, while participants performed the mental MI task. We administered either bilateral transcranial direct current stimulation (tDCS) or sham stimulation for 20 min. above the sensorimotor areas. After stimulation the stimulation electrodes were removed and replaced by EEG electrodes. Then the mental MI task was continued and MI-induced EEG activity was recorded. While participants performed the mental MI task, during and after stimulation, EMG activity was recorded. Following the MI task EMG electrodes were removed and the session ended with the physical motor task and questionnaires. (B) Trial layout for the mental MI task and the physical motor task. The presented stimuli (green fixation cross, red arrow pointing to the left or right) were identical for the mental MI and the physical motor task, while the timing of the stimulus presentation differed between the two tasks. The mental MI task followed the timing indicated on the left side of the time line and the physical motor task followed the timing indicated on the right side of the time line. During the physical motor task participants were instructed to place their index, middle, ring and little finger above predefined keys on the keyboard. Each trial started with the display of the red arrow pointing to the left or right, whereby the direction of the arrow indicated the hand to be used for the sequential finger-tapping task. Participants were instructed to initiate and execute the sequence as fast and accurate as possible. During the mental MI task participants were instructed to imagine the sequential finger-tapping task kinesthetically from the first person perspective for 5 s. Similar to the physical motor task each trial was initiated by the appearance of the red arrow and its direction indicated the hand to be used for the MI task.