Fig. 1

Experimental paradigm. Participants underwent three counterbalanced sessions, including the control session (top panel), attention to shock pain session (middle panel), and attention to counter-stimulation session (bottom panel). Each session included four blocks of 20 painful electrical stimuli delivered at varying intervals of 6–15 s over the right sural nerve. In the attention to shock pain and the attention to counter-stimulation sessions, heterotopic innocuous and noxious counter-stimulation (HICS and HNCS, blue and red blocks, respectively) were applied during the second and third blocks. In the attention to shock pain session, participants were instructed to focus their attention on the shocks and to rate shock pain at regular intervals (black arrows). In addition, they were instructed to rate the coolness of HICS and the pain induced by HNCS at the end of the respective blocks (blue and red arrows, respectively). In the attention to counter-stimulation session, participants were instructed to focus their attention on the counter-stimulation applied on their left forearm (HICS or HNCS). They were instructed to rate HICS or HNCS at regular intervals (blue and red arrows) and shock pain at the end of each block (black arrows)