Interrogating the corticospinal tract with a dual-MEP approach
TMS-evoked measures of corticospinal excitability provide a neuroimaging tool that offers higher temporal resolution than fMRI and better localisation to the motor system than EEG/MEG. A single TMS pulse can evoke MEPs in two muscles which, when appropriately tied to two alternative responses, reveal covert plans for action. I will describe studies using this approach to reveal 1) the automatic priming of the motor system by graspable objects, 2) how the truth seeps all the way into motor cortex before being countermanded by a lie during deception, and 3) how speeded decision-making plays out to suggest a direct and continuous influence of interacting evidence accumulators, each favouring a different decision alternative, on downstream corticospinal excitability.
