Increased Response Preparation Overshadows Neurophysiological Evidence of Proactive Selective Inhibition

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Humans are able to proactively inhibit a particular motor response when provided with a precue in a bimanual selective stopping task (e.g., Maybe Stop Right Hand). We investigated how preparation affects proactive selective inhibition, as previous experiments have been performed in a paradigm where the ability to prepare responses ahead of the go-signal was limited. Participants completed a simple selective stopping task (Experiment 1), in which the bimanual response was known in advance of the go-signal. In a control experiment (Experiment 2), participants completed the typical choice selective stopping task in which the bimanual response was indicated by the go-signal. Single-pulse transcranial magnetic stimulation was delivered prior to the go-signal to index corticospinal excitability in stop-cued and noncued limbs. In addition, a startling acoustic stimulus was delivered concurrent with the go-signal to probe independent stop-cued and noncued response preparation (Experiment 1 only). Consistent with previous findings, neurophysiological and behavioral evidence of proactive selective inhibition was found during the choice selective stopping task. In contrast, the simple selective stopping task revealed an overall increase in corticospinal excitability in both the stop-cued and noncued limbs but no difference between them despite behavioral evidence of selective inhibition. In line with the neurophysiological results, startle trials revealed that when a startle reflex was elicited, both noncued and stop-cued responses were initiated early and synchronously. Results suggest that increased preparatory activation of the stop-cued response overshadows the small selective inhibitory effect typically seen in choice selective stopping tasks with limited advance preparation.

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