Figure 1.

Experimental protocol: Experiment 1 and 2. At the beginning 16 conditioned stimulus (CS) alone trials and 16 unconditioned stimulus (US) alone trials were presented in a random sequence (pseudoconditioning), followed by 100 paired CS-US trials. Thirty CS alone extinction trials were given at the end. Transcranial direct current stimulation (tDCS) was started after 16 pseudoconditioning trials and lasted throughout the first 50 paired trials of the acquisition phase, i.e., across 20 min.