General procedure of mental rotation and the TMS experiment. The order of categories was pseudo-randomized for each subject (upper part). In each block objects from only one category were presented. The different pairs of stimuli were presented for 5000 ms and single pulse TMS was applied every 6000 ms as shown for the first two categories (lower part). TMS stimulation started one second after the first stimulus presentation in each block. ISI = inter-stimulus interval.