P136 Investigating inhibitory processes within the motor cortex during conflict resolution using paired-pulse transcranial magnetic stimulation

Introduction In daily life, we often need to deal with situations in which multiple actions are possible, situations of so-called ‘response conflict’. Several brain regions have been identified as key nodes of a network involved in resolving response conflict. However, how and by which physiological mechanism those nodes finally affect the ‘output station’ of the brain, the primary motor cortex, is unknown. A potential mechanism is the involvement of inhibitory interneurons, which can be directly tested using paired-pulse transcranial magnetic stimulation (TMS). Question Here we test how inhibitory processes within the primary motor cortex change over time during the resolution of response conflict. Methods Participants performed an arrow version of the Flanker task. The arrows were arranged such that they either elicit one response with no conflict (e.g., all arrows point to the same direction) or two competing responses (e.g., the target arrow points towards the opposite direction as the flankers). To track the involvement of inhibitory processes over time short intra-cortical inhibition (SICI) was measured as the change in the amplitude of the motor-evoked potential over the left motor cortex elicited by a single supra-threshold pulse and by a supra-threshold pulse preceded by a sub-threshold pulse. This enabled the identification of time-specific physiological patterns of inhibitory processes at the level of primary motor cortex. Results Preliminary analyses show increased MEP amplitudes towards the response and specific changes in SICI over time dependent on the level of response conflict. Conclusion These results suggest involvement of primary motor cortex inhibitory interneurons when resolving situations of response conflict.