Time course of the state-dependent effect of transcranial magnetic stimulation in the TMS-adaptation paradigm

The transcranial magnetic stimulation (TMS)-adaptation paradigm, based on the state-dependency of TMS effects, may become a useful tool for differential stimulation of functionally distinct neural populations within the stimulated region. Here we investigated, in the context of motion perception, the time course of state-dependent TMS effects in this paradigm. After adapting to a motion stimulus, subjects were asked to perform a motion direction discrimination task, with TMS applied over the motion selective area V5/MT prior to each experimental trial. Consistent with previous studies, TMS reversed the behavioral effect of adaptation; that is, detection of the adapted direction was enhanced and that of the unadapted direction was impaired. Importantly, this reversal was consistent over the whole block of trials carried out after adaptation: the state-dependent TMS effect was similar in the first and second halves of the post-adaptation discrimination block. This shows that while single-pulse TMS interacts with the effects of adaptation on a trial-by-trial basis to induce state-dependent effects, it does not abolish the effects of adaptation; rather, after each trial, the stimulated region returns to a state of adaptation.