Fig. 1

Schematic drawing of the TES-MEP set-up. A transcranial electrical stimulator is connected to subcutaneously inserted needle electrodes bilaterally from the vertex of the skull. A multipulse stimulation consists of 3 biphasic pulses/train, pulse width 0.1 ms/phase, ipi = 1.3 ms. Elicited action potentials in corticospinal axons cross the midline at the decussatio pyramis and are conveyed to LMNs that relay to peripheral motor axons. After passing the neuromuscular junction muscular motor potentials are generated in muscle fibers and recorded at a pair of needle electrodes that are connected to a physiological amplifier