Fig. 1

Schematic illustration of typical electromyographic recordings of single- and paired-pulse transcranial magnetic stimulation of the primary motor cortex as measured in electrodes overlying the abductor pollicis brevis (APB). a When a single magnetic test stimulus (TS) at an intensity above the resting motor threshold is applied to the area of the primary motor cortex corresponding to the APB (at time = 0), a motor evoked potential (MEP) is recorded in the contralateral APB electrode shortly afterward. b In the long-interval intracortical inhibition (LICI) paired-pulse paradigm, a suprathreshold (i.e., above the resting motor threshold) conditioning stimulus (CS) is delivered to the primary motor cortex (at time = 0), which results in an unconditioned MEP. After an interstimulus interval of 100–200 ms (100 ms shown), a second, identical test stimulus (TS) is administered. The resulting conditioned MEP (MEP_LICI) is diminished in amplitude. This inhibition is mediated predominantly by cortical GABA_B receptors.