%0 Journal Article %A J. Ibáñez %A R. Hannah %A L. Rocchi %A J.C. Rothwell %T Excitability changes in the motor cortex in preparation for selfpaced and cue-guided movements: a transcranial magnetic stimulation study %D 2018 %R 10.1101/470153 %J bioRxiv %P 470153 %X Reaction time tasks are characterised by two features: preparatory suppression of corticospinal excitability that precedes facilitation and movement onset; and intersensory facilitation, in which receipt of a second stimulus around the time of the imperative signal shortens reaction times. These are usually explained using a model of subthreshold accumulation of motor commands where preparatory suppression prevents premature release of “subthreshold” commands. Conversely, additional sensory inputs during intersensory facilitation speeds up processing of the imperative stimulus and reduces the time to trigger movement initiation.Here we question that interpretation by studying movements that are self-paced or timed with predictable cues. In the subthreshold model, premovement suppression of excitability should be absent in self-paced movements. Similarly, they should not show intersensory facilitation for the same reasons. Predictable movements also could have no need for either preparatory inhibition or an onset trigger. If their preparation was started at an appropriate time, they would evolve naturally to threshold at the required time. In contrast with these predictions, the results showed that corticospinal excitability evolves over the same time course regardless of movement type. We conclude that inhibition is not a brake on release, it is an integral part of movement preparation. In addition, intersensory facilitation-like effects occur in self-paced movements, suggesting that they require a trigger event before movement is initiated. Unexpectedly, intersensory facilitation is not seen in predictive movements, suggesting they use different triggering mechanisms, or that they involve active suppression of distracting external events.SIGNIFICANCE Intuitive reasoning suggests that planning for a forthcoming movement should involve subthreshold preparation of motor commands. In reaction movements release of these commands is triggered by an external input whereas in self-paced tasks, movement could start as soon as preparation is complete. Here we provide evidence in humans using TMS of motor cortex that this is incorrect. Preparation for movement appears to involve the motor cortex entering a novel state characterised by a small reduction in overall excitability. This is then triggered into execution by either an external event, or, on the case of self-paced tasks, by an equivalent internal event.JI was supported in part by Grant No. #H2020-MSCA-IF-2015-700512 from the European Commission. RH was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) (Grant No. BB/N016793/1). We gratefully acknowledge the technical assistance of Paul Hammond. We also thank Arisa Reka for assistance in collection of data in Experiment 2. %U https://www.biorxiv.org/content/biorxiv/early/2018/11/25/470153.1.full.pdf