[Motor potentials following spinal and transcranial stimulation: normal values for recording without voluntary...

The transcranial motor stimulation with a special, short discharging stimulator can assess the conduction of central motor pathways. Voluntary preinnervation of certain muscles leads to amplitude augmentation and allows reduction of the stimulus intensity. Preinnervation is impossible, if comatose patients are studied or if the method is used for intraoperative monitoring. We examined the spinal and transcranial stimulated motor responses of the muscle opponens pollicis without preinnervation in 18 healthy volunteers. The latencies after hemispheric stimulation showed an increase of latency of more than 2.5 ms compared with normative data from the literature which is significant on the .05-level. The central conduction time was prolonged also. The latencies of the spinal stimulated muscle potentials are comparable under both conditions. It is concluded that for intraoperative monitoring or the assessment of motor function in comatose patients one has to relay on normative values achieved without preinnervation.