P140 Dorsal premotor cortex revisited: Movement-related inhibitory connectivity to the ipsilateral motor cortex

Introduction In non-human primates, the role of the human dorsal premotor-motor circuit in the ability to prepare and to release at the right time is well established. In humans, the dual-coil transcranial magnetic stimulation (TMS) technique allows testing functional connectivity between a chosen portion of the cortex and the primary motor cortex. Objective In the present study, we tested the short-latency effects of conditioning TMS that was delivered to the left dorsal premotor cortex (PMCd) on the output of test TMS that was delivered to the ipsilateral orofacial motor cortex (M1), measured by means of motor evoked potentials. Methods Dual-coil TMS was delivered during the SET-period of a delayed associative task. The task required the performance of mouth movements in response to a GO-signal appearing after a variable, but predictable, waiting period. Such task allowed us to test with TMS the PMCd-M1 circuit specifically during the processes of withholding an action. Results Conditioning TMS delivered 6 ms prior to test TMS exerted an inhibitory effect on the excitability of M1. The inhibition was evident only at specific time-points of the varying set-periods and appeared to be time locked to the onset of the SET-period rather than to the predicted GO-signal. Post-hoc we observed that TMS over PMCd produced significant failure in inhibiting the target action. Conclusion Taken together the data indicate that the behavioural capacity of withholding a given instructed action is at least in part supported by the PMCd-M1 module.