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Behavioral interpersonal coordination requires smooth negotiation of actions in time and space (joint action—JA). Inhibitory control may play a role in fine-tuning appropriate coordinative responses. To date, little research has been conducted on motor inhibition during JA and on the modulatory influence that premotor areas might exert on inhibitory control. Here, we used an interactive task in which subjects were required to reach and open a bottle using one hand. The bottle was held and stabilized by a co-actor (JA) or by a mechanical holder (vice clamp, no-JA). We recorded two TMS-based indices of inhibition (short-interval intracortical inhibition—sICI; cortical silent period—cSP) during the reaching phase of the task. These reflect fast intracortical (GABAa-mediated) and slow corticospinal (GABAb-mediated) inhibition. Offline continuous theta burst stimulation (cTBS) was used to interfere with dorsal premotor cortex (PMd), ventral premotor cortex (PMv), and control site (vertex) before the execution of the task. Our results confirm a dissociation between fast and slow inhibition during JA coordination and provide evidence that premotor areas drive only slow inhibitory mechanisms, which in turn may reflect behavioral co-adaptation between trials. Exploratory analyses further suggest that PMd, more than PMv, is the key source of modulatory drive sculpting movements, according to the socio-interactive context.

Action Execution (AE) and Action Observation (AO) share an extended cortical network of activated areas. During coordinative action these processes also overlap in time, potentially giving rise to behavioral interference effects. The neurophysiological mechanisms subtending the interaction between concurrent AE and AO are substantially unknown. To assess the effect of AO on observer’s corticomotor drive, we run one electromyography (EMG) and three Transcranial Magnetic Stimulation (TMS) studies. Participants were requested to maintain a steady hand opening or closing posture while observing the same or a different action (hand opening and closing in the main TMS study). By measuring Cortical Silent Periods (CSP), an index of GABAB-mediated corticospinal inhibitory strength, we show a selective reduction of inhibitory motor drive for mismatching AE-AO pairs. The last two TMS experiments, show that this mismatch is computed according to a muscle-level agonist-antagonist representation. Combined, our results suggest that corticospinal inhibition may be the central neurophysiological mechanism by which one’s own motor execution is adapted to the contextual visual cues provided by other’s actions. •Inhibitory circuits mediate neural integration of Action Execution and Observation.•Mismatch in action execution and observation modulate cortical silent periods.•Action execution-observation mismatch is computed at the muscle level.•Corticospinal inhibitory mechanisms may guide joint action coordination.

The term affordance refers to the property or quality of an object that indicates the ways in which it could potentially be used. Affordances elicit automatic motor representations that sometimes differ from the current action representation, resulting in behavioural interference effects. This affordance-induces interference could result in automatic and involuntary behavioural inhibition, probably according to the same mechanism that controls the voluntary motor inhibition. Nevertheless, few studies have considered how voluntary response inhibition is modulated by affordance. In this study, we assess the effect of affordance on voluntary action inhibition using a stop-signal task with an affordance object as a Stop Signal. An image of a mug, with the handle orientated in the same or in the opposite direction of the hand recruited to respond at the target, was used as Stop Signal. Our results showed a reduction of the time necessary to withhold the response when the handle of the mug was pointed toward the hand pre-activated to respond. This effect indicates an increased inhibition due to the mismatch between the motor representation elicited by the affordance and the motor representation pre-activated by the target. This suggests a specific interference effect, reflected in an enhanced ability to inhibit an ongoing action.