Fig. 1.

Neurostimulation montage and task design. A. Cortico-cortical paired associative stimulation (ccPAS) consisted of one coil positioned over the right intraparietal sulcus (IPS) (20° tilt posteriorly) and one coil positioned over the right lateral prefrontal cortex (LPFC) (20° tilt anteriorly), under neuronavigation (see insert). B. Illustration of target regions [x,y,z, in Montreal Neuroimaging Index (MNI) coordinates (in mm)]: the right LPFC (blue: 50,16,26), and right inferior parietal sulcus (yellow: 30,–60,50). For visualisation purposes only, we depict an example of the white matter tracts connecting IPS and LPFC coordinates. This illustration was made using previously-published diffusion-weighted imaging data from the Human Connectome Project (healthy subject dataset), employing deterministic tractography on a standardized structural connectome [see previous publication for methodological details and full results (Horn et al., 2017)]. C. The two-step task involved a first level of selection between two symbols, with each having a fixed probability of leading to a subsequent set of stimuli. At the second level, participants selected one of the new symbols, which were each associated with a differential probability of monetary reward. The second-level contingencies (i.e., reward probabilities) shifted slowly and independently over time according to Gaussian random walks; one example is illustrated in Fig. 1C). D. The working memory task began with a fixation cross (500 msec) before presenting either three or six lines rotated around the fixation cross (3 lines in 75 trials; 6 lines in 75 trials; randomised order across trials), also for 500 msec. Last, participants had to rotate a probe line using the mouse, attempting to match its orientation to the line displayed in that location on the previous screen (unlimited time allowed).