Measuring the non-selective effects of motor inhibition using isometric force recordings

Inhibition is a key cognitive control mechanism. When rapidly exerted, inhibitory control has broad, non-selective motor effects, typically demonstrated using cortico-spinal excitability measurements (CSE) elicited by transcranial magnetic stimulation (TMS). For example, during rapid action-stopping, CSE is suppressed at both stopped and task-unrelated muscles. While such TMS-based CSE measurements provide crucial insights into the fronto-basal ganglia circuitry underlying non-selective inhibition, they have several downsides. TMS is contraindicated in many populations (e.g., epilepsy, deep-brain stimulation patients), has limited temporal resolution, produces distracting auditory and haptic stimulation, is difficult to combine with other imaging methods, and necessitates expensive, immobile equipment. Here, we attempted to measure the non-selective motor effects of inhibitory control using a method unaffected by these shortcomings. 30 participants exerted isometric force on a hand-held force transducer while performing a foot-response stop-signal task. Indeed, when foot movements were stopped, force output at the task-irrelevant hand was suppressed as well. Moreover, this non-selective reduction of isometric force was highly correlated with stop-signal performance and showed frequency dynamics similar to established inhibitory signatures typically found in neural and muscle recordings. Together, we demonstrate that isometric force recordings capture the non-selective effects of motor inhibition, enabling many applications that are impossible with TMS.