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Proactive interhemispheric disinhibition supports response preparation during selective stopping

Response inhibition is essential for terminating inappropriate actions. A substantial delay may occur in the response of the non-stopped effector when only part of a multi-effector action is terminated. This stopping-interference effect has been attributed to nonselective response inhibition processes and can be reduced with proactive cueing. This study aimed to elucidate the role of interhemispheric primary motor cortex (M1-M1) influences during selective stopping with proactive cueing. We hypothesized that stopping-interference would be reduced as stopping certainty increased, owing to proactive recruitment of interhemispheric facilitation or interhemispheric inhibition when cued to respond or stop, respectively. Twenty-three healthy human participants performed a bimanual anticipatory response inhibition paradigm with cues signaling the likelihood of a stop-signal occurring. Dual-coil transcranial magnetic stimulation was used to determine corticomotor excitability (CME), interhemispheric inhibition (IHI), and interhemispheric facilitation (IHF) in the left hand at rest and during response preparation. Response times slowed and stopping-interference decreased with cues signaling increased stopping certainty. Proactive response inhibition was marked by a reduced rate of rise and faster cancel time in electromyographical bursts during stopping. There was a nonselective release of IHI but not CME from rest to in-task response preparation, while IHF was not observed in either context. An effector-specific CME but not IHF or IHI reduction was observed when the left hand was cued to stop. These findings indicate that the stopping-interference effect can be reduced through proactive suppression. Interhemispheric M1-M1 channels modulate inhibitory tone that supports responding, but not selective stopping, in a proactive response inhibition context. Significance statement Response inhibition is essential for terminating inappropriate actions and, in some cases, may be required for only part of a multi-effector action. The present study examined interhemispheric influences between the primary motor cortices during selective stopping with proactive cueing. Stopping selectivity was greater with increased stopping certainty and marked by proactive response inhibition of the hand cued to stop. Inhibitory interhemispheric influences were released during response preparation but were not affected by proactive cueing. These findings indicate that between-hand stopping can be selective with proactive cueing, but cue-related improvements are unlikely to reflect advance engagement of interhemispheric influences between primary motor cortices.