AbstractInhibitory control is the ability to suppress inappropriate movements and unwanted actions, allowing to behave in a goal directed manner and to regulate impulses and responses. At the behavioral level, the ability to suppress unwanted actions can be measured via the Stop Signal Task, which allows estimating the temporal dynamics underlying successful response inhibition, namely the stop signal reaction time (SSRT). At the neural level, Transcranial Magnetic Stimulation (TMS) provides measures of electrophysiological markers of motor inhibition within the primary motor cortex (M1), such as the Cortical Silent period (CSP). Specifically, CSP’s length is a neurophysiological index of the levels of intracortical inhibition within M1, mainly mediated by slow GABAB receptors. Although there is strong evidence that intracortical inhibition varies during both action initiation and action stopping, it is still not clear whether interindividual differences in the neurophysiological markers of intracortical inhibition might contribute to behavioral differences in actual inhibitory control capacities. Hence, we here explored the relationship between individual differences in intracortical inhibition within M1 and behavioral response inhibition. The strength of GABABergic-mediated inhibition in M1 was determined by the length of individuals’ CSP, while the ability to suppress unwanted or inappropriate actions was assessed by the SSRT. We found a significant positive correlation between CSP’s length and SSRT, namely that individuals with greater levels of GABABergic-mediated inhibition within M1 seems to perform overall worse in inhibiting behavioral responses. These results support the assumption that individual differences in intracortical inhibition are mirrored by individual differences in action stopping abilities.New & NoteworthyThe present study corroborates the hypothesis that interindividual differences in neurophysiological TMS-derived biomarkers of intracortical inhibition provide a reliable methodology to investigate individual response inhibition capacities. To date, this is the first study to show that interindividual differences in the CSP’s length measured offline provide a viable biomarker of behavioral motor inhibition, and specifically that individuals with longer CSP performed worse at action stopping, compared to individuals with shorter CSP.