The role of the right pre - supplementary motor area in stopping action : two studies with 1 event - related transcranial magnetic stimulation 2 3

18 Rapidly stopping action engages a network in the brain including the right pre-supplementary 19 motor area (preSMA), the right inferior frontal gyrus and the basal ganglia. Yet the functional 20 role of these different regions within the overall network still remains unclear. Here we focused 21 on the role of the right preSMA in behavioral stopping. We hypothesized that the underlying 22 neurocognitive function of this region is one or more of setting up a stopping rule in advance, 23 modulating response tendencies (e.g. slowing down in anticipation of stopping), and 24 implementing stopping when the stop signal occurs. We performed two experiments with MRI-25 guided, event-related, transcranial magnetic stimulation (TMS), during the performance of 26 variants of the stop-signal. In Experiment 1 we show that stimulation of the right preSMA vs. 27 vertex (control site) slowed the implementation of stopping (measured via stop signal reaction 28 time) but had no influence on modulation of response tendencies. In Experiment 2, we showed 29 that stimulation of the right preSMA slowed implementation of stopping in a mechanistically 30 selective form of stopping but had no influence on setting up stopping rules. The results go 31 beyond the replication of prior findings in showing that TMS of the right preSMA impairs the 32 stopping process, including a selective form of stopping, by specifically disrupting 33 implementation of the stop process. Future studies are required to establish whether this was 34 due to stimulation of the right preSMA itself or because of remote effects on the wider 35 stopping network.