NEURAL STIMULATION MAPS THE DYNAMICS OF MOTOR EXCITABILITY AND ITS EFFECTS ON BEHAVIOR DURING REST AND PREPARATION

The excitability of the human motor cortex changes dynamically, which causes moment-to-moment changes in our ability to act quickly and accurately. Here, we present three studies on how such dynamic excitability is modulated by neural oscillations in the beta band, and by temporal cues inducing temporal expectations for when to act. In the first study, we relied on transcranial alternating current stimulation (tACS) to induce beta oscillations. Using a combination of transcranial magnetic stimulation (TMS), electroencephalography (EEG), and electromyography (EMG), we show how such oscillation phase affects cortical excitability. In a second study, we present a temporal preparation task, where different cues induce different expectations on when to act. We measured EEG and analyzed how beta power and phase related to response times. Finally, we present data from a study using a similar temporal preparation task with different cues. As participants prepared a response, TMS pulses were delivered at different moments in the cue-target interval. This was used to uncover how dynamic changes in temporal preparation affect motor reactivity. Taken together, the results paint an intricate picture of how oscillatory activity and temporal expectations interact in the motor cortex, modulating our readiness to respond at any given moment.