Linking cortical and behavioural inhibition: Testing the parameter specificity of a transcranial magnetic stimulation...

Across a series of studies, our laboratory has shown that the efficiency of action stopping is associated with the strength of GABA_A-mediated short-intracortical inhibition (SICI) as measured using transcranial magnetic stimulation (TMS). However, these studies used fixed TMS parameters, which may not optimally probe GABA_A receptor activity for each individual. In the present study, we measured the relationship between stopping efficiency and SICI using a range of TMS parameters. Participants completed a right-hand unimanual stop signal task to obtain a measure of stopping efficiency. Resting-state SICI was measured from the left primary motor cortex using six combinations of interstimulus intervals and conditioning pulse intensities. We also established the parameters which generated the strongest SICI (SICI_max) and weakest SICI (SICI_min) for each individual. We found that stopping efficiency was significantly predicted by SICI using various TMS parameters, including SICI_max. Interestingly, SICI_min accounted for a similar proportion of variance in stopping efficiency as SICI measured using other TMS parameters. The findings suggest that the relationship between stopping efficiency and SICI is robust, reliable, and not influenced by the extent to which SICI is optimally probed.