Motor outcomes of repetitive transcranial magnetic stimulation are dependent on the specific interneuron circuit targeted

Abstract

Different aspects of motor behaviour may engage distinct interneuron circuits in the human motor cortex. If so, the behavioural effects of repetitive transcranial magnetic stimulation (rTMS) protocols may critically depend on the specific circuit stimulated. We used TMS of the hand area to activate two distinct synaptic inputs to corticospinal neurons by altering the direction of current induced in the brain: posterior-anterior (PA inputs) and anterior-posterior (AP inputs). We found AP inputs to be preferentially suppressed during motor preparation in a reaction time task. We also show that preconditioning PA, but not AP, inputs with via rTMS facilitates performance of a ballistic motor task. These results suggest that behavioural effects of rTMS may be most evident when relevant interneuron circuits are targeted.