Fig. 2: Schematic of the N-Back working memory (WM) task.

A Illustration of the two runs, one starting with a Threat block, and the other with a Safe block. The order of runs was counterbalanced across participants. In addition, participants performed the task in two different contexts, safety (Safe blocks) or threat of electrical shock (Threat blocks). Safe and Threat blocks alternated within each run and were paired with difficulty (i.e., 1-Back or 3-Back task). Each run comprised 8 blocks (45 s each) in total, with 2 blocks per task condition (i.e., 1-Back/Safe, 1-Back/Threat, 3-Back/Safe, 3-Back/Threat). B Illustration of a Safe block (letters surrounded by blue color) of a 1-Back task and a Threat block (letters surrounded by orange color) of a 3-Back task. At the beginning of each block, an instruction screen (8000 ms) notified participants of task load, i.e., 1-Back or 3-Back task. Within each block, 18 letters were sequentially presented for 500 ms at 2000 ms interval. Prior to the experiment, participants were instructed that, during the Safe blocks (letters surrounded by blue color), they would never receive an electrical shock, whereas unpredictable electrical shocks could be delivered at any time during the Threat blocks (letters surrounded by orange color). In total, six shocks were delivered throughout the task, three in each run.