When Stopping Requires Going: Physiological Similarities Between Action Cancellation and the Cancellation of Action Cancellation.

The reactive cancellation of real-world actions typically requires complex combinations of both muscle contraction and/or muscle suppression. However, current experimental paradigms solely examine contexts in which action cancellation requires muscle suppression. To provide fundamental insights into inhibitory control mechanisms, we directly compared the latency of action cancellation in novel paradigms where 'stopping' required either suppression of planned activation or reinstatement of ongoing activity. Twenty healthy adults (mean age = 32.2 years) completed novel variants of the stop signal task (SST) in which each trial began with tonic force production to depress two buttons. When a go signal appeared, participants were required to release these buttons. On a subset of trials, a stop signal occurred after a brief delay, and participants were required to cancel the release of one of the buttons. Data in these variants were compared to conventional response-selective SSTs, in which the go signal required bilateral button presses and stop signals necessitated the cancellation of one of these responses. Electromyographic (EMG) recordings allowed a detailed comparison of the characteristics of muscle contraction and suppression (i.e., stopping speed) across these tasks. When physiological evidence of synchronous action cancellation in both hands was observed (supporting recent models of complex stopping), EMG measures of action cancellation speed did not differ (p = 0.863, BF = 8.49) between cancellation of releases and cancellation of presses conditions. This result suggests that response inhibition may broadly characterise reactive control to maintain a current physiological state rather than specific cancellation of a voluntary response.