Pre-Supplementary Motor Area Theta Burst Stimulation Alters Corticomotor Facilitation and Action Reinitiation Without Impairing Response Inhibition
Background The pre-supplementary motor area (preSMA) is increasingly being explored as a neuromodulation target for impulsive behaviour in several clinical populations. Treatment effects are generally interpreted as improvements in inhibitory control. However, healthy studies report improved/impaired/unchanged inhibitory control following identical preSMA stimulation protocols, and few studies examine accompanying neurophysiological changes. We therefore investigated whether preSMA stimulation influences downstream corticomotor excitability to modify a general stopping mechanism, other components of action control, or wider cue-dependent attentional processes relevant to impulsive behaviour. Methods In a preregistered, double-blind crossover study, 18 healthy adults received active and sham continuous theta burst stimulation (cTBS) over right preSMA. Motor-evoked potentials (MEPs), anticipatory response inhibition task measures, and alcohol dot-probe reaction times were collected before and after stimulation and analysed with linear mixed models. Results MEPs increased during sham (p = .028) but not after active cTBS (p = .741). Active cTBS did not affect complete or partial stopping on the response inhibition task. Instead, active cTBS slowed the continuing response after partial stopping (p < .001) whereas response execution sped up across the sham session (p < .001). No alcohol attentional bias or stimulation effect was detected. Conclusions PreSMA cTBS did not impair general inhibitory or attentional control. Instead, it attenuated session-related corticomotor facilitation and selectively slowed reinitiation of a partially inhibited action. These findings suggest that clinical effects to impulsive behaviour from preSMA neuromodulation are primarily rooted in changes to motor preparation and action updating rather than a unitary stopping mechanism.